CN113960702A - Lens assembly and actuator for optical system and method thereof - Google Patents

Abstract

The invention discloses a lens assembly and an actuator of an optical system and a method thereof. A small form factor optical zoom suitable for use in mobile devices (such as cell phones), security cameras, and other small format imaging systems. One or more alvarez lens pairs are provided and move transverse to the optical axis. The combination of one or more alvarez lens pairs with an actuator allows for a zoom capability of at least 3x with a lateral displacement distance of the optical components of about 5mm or less.

Description

Lens assembly and actuator for optical system and method thereof

The present application is a divisional application of an invention patent application having an application date of 2015, year 01, month 08, application number of 201580004170.X, and a PCT international application number of PCT/IB2015/000409 entitled "lens assembly and actuator of optical system and method thereof".

Cross Reference to Related Applications

This application relates to and claims the benefits of PCT application PCT/US13/69288, filed on day 11, 8, 2014, US patent application SN61/925,215, filed on day 1, 8, 2014, US patent application SN61/874,333, filed on day 9, 5, 2013, and US patent application SN61/724,221, filed on day 8, 11, 2012, all of which are incorporated herein by reference.

Technical Field

The present invention relates to lens assemblies and actuators for use in conjunction with imaging sensors, and more particularly to a method and apparatus for providing optical zoom in devices such as cell phone integrated cameras, security cameras, or other small form factor imaging devices, particularly those that benefit from a small Z-dimension.

Background

Actuators for optical systems are typically used to reposition one or more lenses of the optical system relative to an image plane to change the focal length of the optical system. Repositioning is typically intended to achieve focusing or zooming. The actuator for achieving focusing is used to adjust the focal length of the optical system to make the image sharp or sharp. For small-format optical systems, especially in handheld devices such as telephones and the like, electromagnetic actuation systems (also known as voice coil motors) have been used for focusing. In this configuration, the lens is typically moved less than 350 μm along the optical axis for focusing. The electromagnetic system supplies current to the actuator to effect movement of the optical component in a single direction along the optical axis. This movement is counteracted by a spring which pulls the optical component in the opposite direction. The distance moved is thus a function of the current supplied and the spring tension.

The actuator used to achieve zooming repositions one or more lenses of the optical system relative to the image plane, so the focal length of the optical system changes to make distant objects appear closer without moving the camera. For example, 2: a1 zoom lens can make the distance of an object from the image sensor appear to be only half the distance of the zoom lens at the minimum focal length.

The widespread use of various small format optical systems, for example in various small devices such as telephones, tablets, surveillance cameras, etc., poses additional challenges to the actuation system, as the small form factor still requires good performance. In small-scale optical systems, desirable performance characteristics of the actuator system include positional accuracy, low power, low noise levels, and speed. The positional accuracy is important to achieve a desired image quality. Low power consumption is important to extend battery life in various handheld mobile devices and is affected by the required stroke length, the force required to overcome the weight of the moving optics, and friction. Avoiding or reducing noise generated during actuation is important to prevent unwanted noise from being captured by the device microphone during video capture. The speed at which the desired composition and focusing (including zooming) of the image is achieved (which is a function of the speed at which the components move and the distance moved) is important to meet the response time desired by the consumer for the magnified or focused image.

In many modern optical systems, zooming can also be achieved by software means, typically referred to as "digital zooming". Digital zoom is a method of reducing (zooming out) the angle of view of a digital photographic or video image. Digital zooming is achieved by cropping the image down to a central area with the same aspect ratio as the original image. Digital zooming is done electronically without adjusting the optics of the camera and without increasing the optical resolution in the process. Cropping results in a reduced quality image. In many cases, digital zooming also involves interpolating the results back to the original's pixel size. This combination of cropping and magnification of pixels typically produces a pixelation/mosaic effect in the image and typically introduces interpolation artifacts. This pixelation typically results in a significantly reduced quality image. Furthermore, digital zoom is typically implemented as a series of increments, rather than as a continuous zoom. Thus, for example, some digital zooms are implemented in tenths of a power increment, while others use larger increments. This corresponds to a reduction in the effective size of the sensor.

Some prior art attempts to overcome the disadvantages of digital zoom by providing oversized sensors (e.g., forty-one megapixels). In this arrangement, the reduction of the field of view of the view and hence the clipping inherent in digital zoom still illuminates (illuminate) a considerable megapixel. Thus, the final scaled image appears more acceptable even if cropped in a conventional manner. In one version of this prior art design, a full size sensor is said to be used at the full field of view (or maximum wide angle), but a 2x zoomed image uses only about eight megapixels of this sensor, and a 3x zoomed image uses only about five megapixels of the sensor.

However, in addition to being very expensive for most such devices, oversized sensors are physically larger than those desired for mobile devices (such as cell phones, etc.). In addition, larger sensors also require a longer optical path to the sensor to ensure that the image covers the entire sensor. Thus, there is still often a z-axis protrusion, not just the larger x, y values of the sensor.

Unlike digital zoom, optical zoom has long been used in photographic and other optical systems to provide zoom without loss of image quality. A typical lens system that provides optical zoom by using concave or convex lens elements moves one or more lens elements along the optical axis, and in most such systems, the optical center of each lens element is located on the optical axis. While such systems may provide good image clarity, they require the lens element to travel an excessive distance to be suitable for many applications requiring small form factors. For example, in a camera used in a mobile phone, the electronics of the mobile phone impose a strict limitation on the outer dimensions of a lens module used in the camera of the mobile phone, and such a limitation prohibits the use of conventional optical zoom.

While some cell phones have provided lens systems that provide optical zoom for use with their integrated cameras, these typically add a significant amount of thickness to the cell phone, at least at the area of the lens system of the camera. Furthermore, prior art optical zoom (where the lens is moved along the optical axis), which is capable of 3 magnification for example, typically requires the optical components to move more than 10 mm. Such a long travel range typically requires the use of a stepper motor. This is undesirable for small-format optical systems used in mobile devices because they are bulky, require more power to move such long distances, and may cause noise picked up by the device's microphone. Other actuation systems include piezoelectric motors to actuate optical elements parallel to the optical axis to establish optical zoom and auto-focus. However, piezoelectric motors also tend to be acoustically noisy and create problems with hysteresis that require more complex electronics to overcome. Piezoelectric motors tend to use more power than some other designs. Furthermore, systems using conventional meniscus lenses to provide optical zoom require significantly longer strokes than currently desired, thereby increasing battery consumption and requiring significantly larger form factors for the lens module.

Accordingly, there has long been a need for small form factor optical systems suitable for use in mobile devices (such as cell phones and the like) or other small format systems that provide clear optical zoom.

Disclosure of Invention

The present invention provides a small form factor optical zoom suitable for use in mobile devices (such as cell phones, etc.), security cameras, and other small format imaging systems. To achieve the small form factors required for these devices, one or more Alvarez (or Lohmann) lens pairs are provided and moved transverse to the optical axis by means of the actuators described herein.

In an embodiment, the combination of one or more alvarez lens pairs and an actuator allows for a zoom power of up to 6x below a lateral displacement distance of the optical element of about 5 millimeters. The optical system is thus well suited for a mobile phone device and can also be easily implemented as a lens module having a very small form factor (e.g., 10X10X6mm [ X Y X Z ] or less). Zoom powers larger than 6x can be achieved with displacements of less than 10mm, although the profile is slightly larger. Larger form factors are also acceptable according to embodiments, such as 30x30x6 mm. In some embodiments, the Z height is less than 6mm, e.g., less than 5.8 mm. In addition to providing sharp, low profile optical zoom, the system of the present invention also provides the advantages of very low power consumption and low noise. Furthermore, the actuator of the present invention has the additional advantage of minimal magnetization degradation throughout the plane of travel.

The invention also includes a method for optimizing the spacing between one or more pairs of alvarez (or lomann) lenses (hereinafter sometimes also referred to as free-form lenses for convenience) configured to establish an optical zoom system in which the lenses are moved transverse to the optical axis. Each of the free-form lenses may have one or more free-form surfaces. In some embodiments, each lens of the pair of free form lenses has one flat surface and one free surface, wherein the free form surfaces face each other. The distance or gap between the lenses is carefully selected to ensure that the lenses do not contact each other while minimizing or reducing optical aberrations as they are moved transverse to the optical axis to provide magnification.

In an embodiment, translation of the free form lens relative to the other provides focusing and magnification, or zooming. In an alternative embodiment, translation of the free-form lens provides magnification, while the base lens is actuated separately to provide focus. In some embodiments, the base lens is actuated along the optical axis and comprises one or more concave or convex lenses.

In an embodiment, the zoom is continuous throughout the range of focal lengths provided by the system. In an alternative embodiment, one or more locking positions are used to provide discrete zoom increments. In an embodiment, the locked position is maintained by one or more magnetic locks, while in another embodiment, a mechanical lock is used.

It is therefore an object of the present invention to provide a camera lens module with optical zoom that is dimensioned to fit within a small device, such as a smartphone, without increasing the height of the smartphone.

It is another object of the present invention to provide optical zoom in a lens module configured to fit within the required form factor of a camera integrated into a smartphone.

It is another object of the invention to provide an optical system comprising an actuator and at least one lens pair, wherein the actuator moves the lens in a direction that is not parallel or collinear with the optical axis of the system to achieve zooming and focusing.

It is another object of the invention to provide an actuator for a lens system suitable for use in a smartphone, a continuous zoom lock maintaining the position of at least one free-form lens.

These and other objects of the present invention will be better understood from the following detailed description taken in conjunction with the following drawings.

Drawings

Fig. 1 illustrates in block diagram form an optical system including a laterally actuated optical zoom in accordance with the present invention.

Fig. 2A illustrates in an exploded perspective view an embodiment of an actuator for a variable focus lens package to move one or more lenses of the package transverse to an optical axis.

FIG. 2B illustrates a partial assembly of an embodiment of a variable focus lens package and an actuator, including showing a magnet assembly for the actuator.

Fig. 2C shows an embodiment in which the zoom lens and the actuator are fully assembled.

Fig. 2D shows an alternative embodiment to some aspects of the variable focus lens package of fig. 2C, wherein the lens frame is accommodated in a recess of the housing, thereby avoiding the need for one or more guide frames.

FIG. 3A illustrates an embodiment of a focusing lens group including an actuator in an exploded perspective view.

FIG. 3B illustrates an embodiment of a focusing lens group partial assembly with an actuator.

FIG. 3C illustrates an embodiment in which the focusing lens group with the actuator is fully assembled.

Fig. 4A illustrates an optical path of an embodiment including the zoom lens group as shown in fig. 2A and the focusing lens group as shown in fig. 3A (in which an alvarez lens pair is arranged at a wide-angle position) for the present invention.

Fig. 4B illustrates an optical path of an embodiment for the present invention including a zoom lens group as shown in fig. 2A and a focusing lens group as shown in fig. 3A, in which an alvarez lens pair is arranged at a zoom or telephoto position.

Fig. 4C illustrates how the equivalent effect of an alvarez lens pair produces an opposite concave surface and an opposite convex surface, depending on the position of the lenses of the alvarez pair relative to each other in their travel.

Improved alvarez lens pairs, wherein both sides of each alvarez lens pair are rotationally asymmetric and defined by appropriate polynomials.

A lens system suitable for use in a small environment such as a cell phone, security camera or related system where two alvarez lens pairs provide optical power, where the two lenses in each lens pair have dual rotationally asymmetric surfaces.

FIG. 5 illustrates an embodiment of a dual coil Voice Coil Motor (VCM) suitable for use in the actuator of FIG. 2A.

Fig. 6 illustrates the lens holder shown in fig. 2 having a shield (armor) for holding the double-coil VCM as shown in fig. 5.

FIG. 7 illustrates various coil and magnet sizes used in a VCM according to an embodiment of the present invention.

FIG. 8 illustrates, in perspective view, an embodiment of the invention in which the actuator is configured to move one lens from each of two pairs of Alvarez lenses together in a direction generally transverse to the optical axis in a configuration generally referred to as 1-4, 2-3.

FIG. 9 illustrates, in perspective view, an embodiment of the invention in which the actuator is configured to move one lens from each of two pairs of Alvarez lenses together in a direction generally transverse to the optical axis in a configuration generally referred to as 1-3, 2-4.

Fig. 10 shows an embodiment in which a mechanical stop (stop) or lock is cooperatively established by the guide frame and its associated lens frame.

FIG. 11 illustrates a magnetic lock used in some embodiments of the invention.

Fig. 12 illustrates a side view of the magnetic latch of fig. 11.

Figure 13 illustrates an embodiment of the invention in which the guide frame limits the travel of at least one alvarez lens element.

Fig. 14A-14B illustrate two different designs for a discrete position magnetic lock suitable for use with some embodiments of the present invention.

Fig. 15 illustrates an embodiment of the present invention in which the magnetic lock includes an on/off coil.

FIG. 16 illustrates an embodiment using magnetic locking with multiple discrete positions.

Fig. 17 illustrates the use of a position sensor to identify the position of the lens frame throughout its lateral travel.

FIG. 18 depicts a generalized model of an Alvarez lens or lens pair.

Fig. 19 shows the effective aperture that appears as each lens in an alvarez pair moves through its stroke.

Fig. 20 illustrates in simplified form the interaction of two alvarez lens pairs with a central aperture coupled to a base lens for focusing an image on an image plane.

Fig. 21 illustrates the fixed interaction of the adjustable lens for creating an image on the image plane.

Fig. 22 illustrates the use of different materials in opposing elements of an alvarez lens pair, where the different materials assist in reducing or eliminating aberrations or other deviations.

Fig. 23-28 illustrate alternative embodiments of actuators and lens systems according to embodiments of the invention.

Fig. 29A-29D illustrate the active optical regions of an alvarez pair at various positions and techniques for improving lens manufacturability by modifying the lens profile.

Fig. 30A-30D illustrate a technique for finding the x and y positions and center of a freeform surface.

31A-31D illustrate a technique for ensuring free-form lens alignment during manufacturing.

Fig. 32D-32G illustrate operation of a cam driven actuator capable of separately positioning each side of multiple alvarez pairs (e.g., moving each of four alvarez lenses arranged within two alvarez pairs through separate strokes).

Fig. 33A-33B illustrate the operation of a linear cam actuator that is also capable of moving multiple lenses through a single stroke.

Fig. 34A-34B illustrate a gear drive actuator and a friction drive actuator adapted to move an alvarez lens transverse to its optical axis.

Detailed Description

Referring first to fig. 1, an optical system 100 including auto-focus and optical zoom is shown in the form of a system block diagram. In particular, the camera module 105 may cooperate with a processor module 110, such as integrated into a smartphone, although the camera module of the present invention may also be implemented independently of a smartphone, such as a webcam or other form of image capture device that is small or miniature in size where optical zoom is desired. In a camera module, when a user wants to take a picture (for convenience, the user drive input is not shown in fig. 1), the drive circuit 115 sends a current to the lens module 120 and, in an embodiment, initially to the focus actuator 125 to allow the user to see a sharp image. A focus actuator (described in more detail below) uses an image signal processor ("ISP") 140 to provide the necessary feedback to the drive circuit 115 to implement any suitable auto-focus method known in the art, such as contrast focus (contrast detection), to automatically adjust the position of the focus lens group 130 until a clear image is obtained at the sensor 135. The autofocus loop can be understood from the dashed line in fig. 1. It will be understood that although ISP 140 is shown in fig. 1 as being within the telephone processor, in at least some embodiments the ISP is contained within lens module 105. In some embodiments, particularly those implemented in smartphones, the output from an autofocus algorithm present in the smartphone processor is converted to an input that can be recognized by the focusing portion of the drive circuit.

If the user wants to magnify an object as indicated by a user input (again not shown in fig. 1 for convenience), the drive circuit 115 supplies current to the zoom actuator 145 within the lens module 120. A zoom actuator (described in more detail below) moves the zoom lens group 150 back and forth until a user indicates that the amount of zoom is acceptable. At the sensor, the zoom lens group and the auto-focus lens group cooperate to achieve magnification and image sharpness. Importantly, for the small form factor invention described herein, the zoom actuator moves the zoom lens in a direction generally transverse to the optical axis, and in embodiments in a direction substantially perpendicular to the optical axis. In particular, the zoom lens includes one or more pairs of free-form lenses (such as alvarez lenses or loeman lenses) rather than the conventional concave or convex lenses typically found in prior art optical zoom systems that achieve focus and zoom by moving the lenses along the optical axis. It will be appreciated that in all embodiments, the lateral movement need not be substantially vertical, so long as suitable magnification and acceptable clarity are achieved.

Once the user is satisfied with the amount of magnification of the image and its sharpness, the user "takes" a picture by having the ISP 140 and the Graphics Processing Unit (GPU)155 capture the image from the sensor 135. It will be understood that GPUs are typically embedded within modern smart phones, but in at least some embodiments of the invention, the processor remains within a different type of device (such as a camera, computer system, tablet, etc.).

The zoom actuator and associated zoom lens group of the present invention may be better understood with reference next to fig. 2A-2D. A free form lens housing cover 200 is located on top of the variable focus lens package assembly, as shown in partially and fully assembled form in FIGS. 2B and 2C. The housing cover 200 fits over the first free-form lens cover 205, which in turn is located over the first free-form lens assembly 200, which includes a first free-form lens mounted in a lens frame on a support, as described in more detail below in conjunction with fig. 5 and 6, and so forth. The holder (as discussed in connection with fig. 6) is further adapted to house at least a portion of a mechanism for moving the first free-form lens laterally with respect to the optical axis. In an embodiment, the mechanism is a voice coil motor, although the motion-inducing mechanism may also be a piezoelectric motor, a Shape Memory Alloy (SMA), or other suitable device. For convenience, the motor will be VCM used hereinafter, although it will be understood that other forms of motor are acceptable, other than as defined by the claims.

First lens subassembly 210 fits into first guide frame 215, which is positioned over second free-form lens subassembly 220. The subassembly 220 includes a second freeform lens mounted over or integrated with the prism for redirecting the optical axis in the manner shown by the ray paths depicted in fig. 4A-4B, and an arm on which the lens frame is mounted for supporting at least the second freeform lens and the coil of the VCM discussed in connection with fig. 5 and 6.

Together, subassemblies 210 and 220 form a first free-form lens pair, and in some cases, hereinafter, subassemblies 210 and 220 are referred to as lens one and lens two. The subassembly 220 fits within a base 225 having the subassembly 210 and an associated guide frame and cover on top of the subassembly, as better shown in fig. 2B and 2C. In the embodiment shown in fig. 2A, a third free-form lens subassembly 230 is shown that also includes an arm having a lens frame in which a third free-form lens is mounted. It will be appreciated that the third sub-assembly 230 is at right angles to the first and second sub-assemblies 210 and 220 to account for variations in the optical axis caused by the prisms. Second guide frame 235 is positioned above third subassembly 230 and fourth free form lens subassembly 240 is received within guide frame 235. It will be understood that the lenses of the third and fourth subassemblies constitute a second pair of free-form lenses, and will be referred to hereinafter in some cases as lens three and lens four.

Pairs of magnet structures 245 are held within the shroud and housing 250, wherein the pairs of magnet structures form VCM pairs (one for each) with the coils mounted on the first and second subassemblies. In an embodiment, magnet structure 245 comprises a plurality of permanent magnets (e.g., three) adapted to cooperate with two VCM coils in each VCM to form a dual coil VCM for the first and second subassemblies. A second pair of covers 255 is positioned over the fourth subassembly to enclose the variable focus lens package and the actuators, as better understood from fig. 2B and 2C.

In an embodiment, the third subassembly and the fourth subassembly do not include any portion of the VCM. In contrast, for the embodiment shown in FIG. 2A, the third subassembly includes an extension 260 that remains perpendicular to the rest of the arm. The extension fits into a groove 265 on the first subassembly 210 so that the first lens and the third lens move together. Similarly, the fourth subassembly arm includes an extension 270 that fits into a recess 275 in the second subassembly, such that the second lens and the fourth lens move together. This configuration (which will sometimes be referred to hereinafter as the 1-3, 2-4 configuration) can be better understood from FIG. 8. In an alternative embodiment, the fourth lens subassembly may be mounted to the first lens subassembly and the third lens subassembly may be mounted to the second lens subassembly, resulting in the 1-4, 2-3 configuration shown in FIG. 9. In yet another alternative embodiment, the third and fourth subassemblies may comprise a VCM and move independently of the first and third subassemblies, although this embodiment would require larger form factors and would typically use more power. Further, other embodiments may include two or more lens elements mounted on the same actuator arm that move in conjunction or independently to align the lens elements. Given the teachings herein, one of ordinary skill in the related art will recognize a variety of alternatives to the specific embodiments illustrated herein that are different from the basic inventive structures and methods discussed.

Referring more particularly to fig. 2B and 2C, it can be seen that the sub-assembly of four free-form lenses forms a compact, miniature optical zoom lens assembly, as indicated at 280A (partially assembled) and 280B (fully assembled). Fig. 2B also illustrates more clearly coil 285, which is mounted on the second subassembly and forms the VCM together with magnet structure 245 to the left of housing 250. Similarly, the other magnet structure 245 shown to the right of the housing and magnetic shield 250 cooperates with the coil on the first subassembly to form the VCM for that structure.

Referring next to fig. 2D, an alternative embodiment of the guide frame is shown. In the configuration of fig. 2D, the housing 286 includes a recess 288 for receiving the first and second lens frames 290, 292, on which the first and second free-form lenses (not shown) are mounted, respectively. Similarly, but mounted vertically rather than horizontally, the third and fourth lens frames 294 and 296 are received within a recess 298 in the housing 286. This configuration allows for reduced part count and simplified manufacturing compared to the configuration of fig. 2A-2C.

Referring next to fig. 3A-3C, the focusing lens group (sometimes referred to simply as the base lens group) may be better understood. The focusing lens group moves the meniscus lens group along the optical axis and, in embodiments, provides focusing and distortion correction with respect to the zoom lens group. Structurally, base lens cover 300 encloses the top of base lens barrel 305, which is contained within base lens holder 310. The pair of compression springs 315 and associated rods 320 fit into the holes of the base lens holder to provide a counterbalancing force against the VCM pair consisting of coil 325 and pair of magnet structures 330. The magnet structure 330 is housed within the holder 310 with the coils mounted to either side of the barrel 305 and fitting into the spaces between the magnets on either side of the structure 330, thereby providing a lorentz force to the barrel when current is supplied to the coils. In some embodiments, where current of opposite polarity is supplied to cause bi-directional motion, spring 315 may not be necessary. Lens element 335 fits within barrel 305 and is held in place by a baffle 340, which may also serve as a mechanical stop for positioning the lens. In some embodiments, the stop may be located between the lenses.

A partially assembled focusing lens group and actuator is shown in fig. 3B, as indicated at 300, 310 and 345. The fully assembled actuator and lens assembly is shown in fig. 3C, as indicated at 350.

4A-4C, the optical relationship between the elements of the zoom lens group and the elements of the focus lens group may be better understood, where FIG. 4C generally illustrates the shape of the pair of Alvarez lenses referred to in FIGS. 4A-4B. More details regarding alvarez lens pairs may be found in co-pending U.S. patent application s.n.14/246571 entitled MEMS-based zoom lens system, filed on 7/4/2014, in the name of singapore national university, which is incorporated herein by reference, and international patent application PCT/US13/69288, which is assigned to the same assignee as the present invention and is also incorporated herein by reference. With respect to fig. 4C, it should be understood that although two pairs are shown side-by-side for convenience, one pair is located in front of (or includes) the prism and the other pair is located behind the prism, as shown in fig. 4A-4B.

In the embodiment of fig. 4A, the arrangement of a free-form (sometimes also referred to as a zoom) lens is shown with the lens in a wide-angle position (shown as "WA"). For illustration, in this position, the first alvarez pair 400 may be represented as having two opposing concave surfaces. Referring to fig. 4C, it can be seen that the lateral position of the alvarez pair is depicted as 470. It will be appreciated that the top surface of the prism 405 may be formed as an alvarez surface, or may be a separate lens from the alvarez surface located above the prism, or may be a separate alvarez lens bonded to the prism in a manner well known in the art. Again for simplicity, the second alvarez pair 410 is shown with two opposing convex surfaces in the wide angle position and a substantially flat surface at the exit of the zoom lens group. In fig. 4C, this lateral position of the alvarez pair is shown at 480. As will be understood hereinafter, in various embodiments, the alvarez pair has rotationally asymmetric surfaces on both sides, rather than flat surfaces, and more of any given combination in the transverse stroke is more complex than a concave or convex pair. Focusing lens group 415 includes conventional convex-concave optics and sends the image to sensor 420. These rotationally symmetric lenses may comprise one or more groups, and may comprise from 1 to 4 or more such lenses according to embodiments.

In the embodiment of FIG. 4B, the free-form lens pair is shown in a zoom state (shown as "Z"). The first lens pair 450 may be represented as two opposing convex lens surfaces and the second pair 460 may be represented as two opposing concave surfaces, as shown in fig. 4C. The focus group and sensor remain the same as in fig. 4A.

Importantly, and as discussed in more detail below in connection with fig. 18, in an embodiment suitable for use in a lens module for a mobile phone, when implementing 3: 1, the lateral translation required to move the lens from the wide angle position to the zoom position is only about 2 millimeters. This shorter stroke allows low power operation with low noise in addition to the desired small form factor. In such an arrangement, the size of the lens typically ranges from 4 to 10 millimeters depending on the desired form factor and the size of the sensor. In other arrangements, different lens sizes would be suitable. Further, in some embodiments, the alvarez lens pair may have rotationally asymmetric surfaces on both sides of each lens in the lens pair, such as lens pairs 485 and 490 shown in fig. 4C, where each surface of each lens in the two pairs is defined by a suitable high order polynomial. It will be appreciated in view of the teachings herein that in some embodiments not all surfaces are rotationally asymmetric. Fig. 4C shows a system in which the first alvarez lens pair 400' is free-form on all four surfaces. The light passes through the lens pair 400' and then bends the light path through the prism 405A. According to embodiments, the prisms may be glass or plastic, even though some glass prisms may provide better aberration performance than plastic prisms. The light then passes through a second alvarez lens pair 410', which is also rotationally asymmetric on all four surfaces. In some embodiments, an additional lens may be inserted between prism 405A and pair 410' to provide image stability. After pair 410 ', the incoming light passes through base lens 415'. The base lens 415' assists in focusing and may include one or more lenses, for example four or five. Depending on the embodiment, the lenses may be designed to move together or separately. The light passing through the base lens is thus focused directly on the sensor 420 'or on the sensor 420' after passing through the second prism 405B. The second prism may be used in embodiments where a lower Z height is desired while still allowing the use of a larger sensor (such as 1/2 "providing, for example, sixteen megapixels).

Referring next to fig. 5, an embodiment of a dual coil actuator that results in relative motion between alvarez lenses may be better understood. In fig. 5, a lens set a (shown as 500) is fixed to a dual coil 510 located on the left side and connected in series. The coil 510 is located between three permanent magnet pairs 515. Similarly, lens set B (shown as 505) is secured to dual coils 510 located on the right and connected in series. A magnetic shield 520 (fig. 2A) surrounds the magnet and coil to prevent leakage of magnetic flux. By supplying current to the coil 510, lorentz forces are generated and the lens assembly is moved in the direction indicated by the arrows on both sides of the coil 510. In some embodiments, a compression spring is included to balance the lorentz force such that when current is removed from the coils, the spring automatically returns the lens set to the rest position. In other embodiments, currents of opposite polarity are supplied to move the lens set in both directions. In embodiments, one vertical leg of the coil conductor is held in one pole region, while the return (return) exists in the opposite pole region. Furthermore, as shown in connection with fig. 2A-2D, in an embodiment, typically one lens of each pair in a 1-3, 2-4 configuration or a 1-4, 2-3 configuration (although other configurations are possible as discussed above in connection with fig. 2A-2D) moves together.

Referring next to FIG. 6, subassembly 210 (FIG. 2A) may be better understood. In particular, the arm 600 provides a first lens frame 605, into which lens frame 605 a first lens (not shown in fig. 6) is mounted in a conventional manner. A recess 610 is integrated into arm 600 to allow sub-assembly 230 or sub-assembly 240 to be secured to sub-assembly 210 depending on whether a 1-3, 2-4 configuration or a 1-4, 2-3 configuration is preferred. For other configurations, the groove 610 may not be necessary. On the underside of the arm 600, the pair of coils 510 is mounted, typically using an adhesive or encapsulation technique. In embodiments, generally in the portion shown in fig. 2A other than the lens itself and the coil and magnet, the arm and lens frame are integrated and formed in a uniform manner, such as by injection molding of materials well known in the art. The new process for moulding such a material is described in more detail in international application PCT/IB2013/002905, which is assigned to the same assignee as the present application and is incorporated herein by reference.

Referring next to FIG. 7, the balance of a magnetic structure with an air gap can be better understood. The objective of the VCM of the present invention is to be able to move optics smoothly and accurately, which requires that regardless of the position of the host device (e.g., smartphone), the VCM is able to generate sufficient lorentz forces to overcome the gravitational and frictional forces of the associated components. In addition, the VCM is typically required to meet full stroke requirements with minimal drop across the stroke plane. Still further, it is desirable for the actuation mechanism to maintain a degree of holding force at the stop or locked position, even when no current is passing through the coil. In some embodiments of the invention, only a single coil may be implemented. However, the dual coil design discussed above and illustrated in fig. 7 more efficiently utilizes the magnetic flux obtained from magnet 515. More specifically, since the magnets must be spaced far apart, the dual coil configuration allows for the use of an increased number of turns of wire on the coil without the disadvantage of increasing the air gap, which is typically associated with an increased number of turns. As shown in fig. 7, which illustrates a five millimeter gauge, it can be seen that the coil 700 is relatively thinner than the magnet. In contrast, coils 710 and 720 are larger (have more turns) and provide a larger lorentz force than coil 700. Further, the VCM for coils 710 and 720 includes a locking mechanism, as discussed beginning at FIG. 11 below.

Referring next to fig. 8 and 9, the 1-3, 2-4 configuration and the 1-4, 2-3 configuration for moving the alvarez pairs in fig. 2A-2D can be better understood. In fig. 8, which depicts a 1-3, 2-4 configuration, the arms on which lens one and lens three are mounted are fixed to each other such that the VCM associated with subassembly 210 (fig. 2A) moves lens one and lens three. Similarly, the arm on which lens two and lens four are mounted is fixed such that the VCM associated with subassembly 220 (FIG. 2A) moves lens two and lens four.

Referring next to fig. 10, an embodiment of a lens frame and guide frame is shown in which mating tabs and notches allow for a locked or stopped position. Specifically, the protrusions 1000 on the guide frame 215 or 235 mate with one or more notches 1005 on the lens frame 605, thereby providing a mechanical lock point along the travel of the arm 600. By providing two indentations 1005, there are two locking positions. For example, one locked position may be at wide angle and another locked position at full zoom. However, to implement such a design, the guide frame, or at least the protrusions 1000, need to flex or bend enough to allow the lens frame to pass through it, depending on the lorentz force applied. It will be appreciated that the locations of the protrusions and indentations may be reversed such that the protrusions are on the optic portion.

Fig. 11 and 12 illustrate an embodiment of a method of providing magnetic locking, wherein fig. 11 is a top cross-sectional view and fig. 12 is a side cross-sectional view. As shown in fig. 11, a locking magnet or ferromagnetic pin or plate 1100 is secured to the associated coil 510 and positioned proximate a gap 1105 in the magnetic shield 520. Gap 1105 is sized to represent all or a portion of the travel of the VCM. In the first position, magnet 1100 is on one side of gap 1105 and in the second position magnet 1100 is on the opposite side of gap 1105. As shown in FIG. 11, the locking pin or magnet may be positioned to lock at the extreme end of the VCM travel, or only at one end, or anywhere in between. However, in some embodiments, a larger initial current must be supplied to the coil 510 to disengage the actuator from the locked position. As an additional feature, an algorithm is implemented in the processor module that causes the drive circuit to move the actuator to the locked position in the event of an impact to the master device.

Referring next to fig. 13, a guide frame 1300 is illustrated that may be configured to: an embodiment that provides a two position mechanical stop for designs that use magnetic locking. Specifically, the guide frame 1300 houses a lens frame and a lens (es) 1305. At either end of guide frame 1300 are stops 1310 and 1315, which provide a mechanical "stop" for the travel of arm 600. Further, in order to reduce friction by reducing a contact surface, a protrusion or protrusion 1320 may be provided on the guide frame 1300 or on the arm 600.

Referring next to fig. 14A-14B, two different designs for magnetic locking of discrete positions are shown, which are suitable for a dual coil VCM for implementing the embodiments discussed above. In fig. 14A, the gap 1400 extends over two coils and two locking magnets or pins 1100 are used in the manner discussed in connection with fig. 11. In fig. 14B, the gap 1400 extends only over a single coil and only a single locking magnet or pin 1100 is used.

Fig. 15 shows an alternative embodiment for magnetic locking, where the small coil 1500 pair is located within the housing 1510 at a position along the travel of the arm and lens holder 600 that represents the locking point. In the illustrated embodiment, a single magnet or pin 1100 is located on the arm 600. When the appropriate one of the coils 1500 is energized, the magnet is attracted to the coil and the arm locks in one of the two coil positions. This embodiment also has the advantage if magnets are used for the pins 1100: the reversal of the current may repel the magnet so that no additional lorentz force is required to overcome the latching force.

Fig. 16 illustrates an embodiment that provides a plurality of discrete locking positions, wherein a plurality (e.g., four) gaps 1600 are formed within the shroud 520. A plurality of locking magnets 1605 (e.g., three in the illustrated embodiment) are positioned below the associated coils 510 such that the coils move from gap to gap when a lorentz force of appropriate magnitude and duration is applied.

Fig. 17 shows yet another alternative embodiment for positioning the zoom actuator across the entire stroke, which provides a substantially continuous zoom option, rather than the incremental, discrete zooms provided in other embodiments with only a few fixed positions. More specifically, a position sensor 1700 (e.g., a hall effect sensor or inertial sensor) is located on the assembly housing 520. Positioned proximate to the position sensor 1700 is a magnet 1705. The sensors 1700 are monitored in a closed loop configuration as the arm 600 travels within the guide frame 215, which allows the arm to be positioned at substantially any selected position throughout its travel. For example, if the output of the sensor is 8 bits of data, it may be 256 locations, and for 10 bits of data, it may be 1024 locations. The number of possible positions is only limited by the signal steps available in the output and the number of sensor steps that can be read. For such a large number of increases, the user feels that the zooming is continuous.

In this embodiment, each position sensor is calibrated after the assembly process and throughout the range of travel. The correction data is stored in the drive circuit or other convenient location in the host device. Closed loop control using position sensor 1700 may be implemented, for example, in a driver circuit, or may be part of a software layer within a controller of a host device. In embodiments employing motion control, the change in gravity of the structure as the camera tilts or rotates is preferably taken into account in a closed loop process. Mechanical or magnetic locking may also be used in some embodiments to implement motion sensing, provide shock protection or reduce power consumption, or to remain in place when stationary.

It should also be appreciated that position sensing may be used to calibrate the position of the lens elements to accommodate any degradation in image quality caused by manufacturing tolerances. By adjusting the lateral position of the lens pair during calibration, the optimum position data can be stored in a drive circuit or other data storage location in the device and applied to the lens module when power is supplied.

In an embodiment according to the invention, a3 times zoom is achieved in less than 0.2 seconds by using a lateral displacement of 2mm substantially perpendicular to the optical axis with a moving mass of 0.2-0.3 g. The lorentz force applied to achieve this result is in the general range of 10-50 millinewtons, depending on the amount of current applied. The applied current to achieve this force is less than 120 milliamps at a power of about 0.1 watts. In this embodiment, the position accuracy is within 30 μm without a position sensor, and within 10 μm with a position sensor operating closed loop. Furthermore, this operation is performed at a noise level below 25 dBA.

Referring next to FIG. 18, another aspect of the invention may be better understood. From fig. 4A-4C, the effect of the lateral movement of the lens elements of the alvarez pair can be understood. In some embodiments, in addition to lateral movement, the gap between the lenses is also important. In large systems, the effect of the gap may be less due to the gentle surface profile. The gentle slope minimizes the deviation of the light as it travels between the two optical surfaces. However, as the optical system and lens diameter size decreases, this approximation becomes inaccurate. Both the optical power and the travel distance of the lens affect the overall slope of the freeform surface. As the gap increases, the deviation of the traveling path of the light passing through the gap increases. This bias is undesirable when analyzing an approximate model of the system.

On the other hand, how small the gap may be is limited. The optical power, the displacement of the movement of the lens, the effective aperture of the system all affect the slope of the freeform surface and how close the two surfaces can be placed in operation. Having a free-form surface with a wave-like shape, contact can occur around the lens surface when the lens is moved laterally. Minimizing the small form factor also limits the optical configuration. To achieve the best image quality within the spatial constraints, the optical power of the tunable lens is limited.

As shown in fig. 18(a), a set of alvarez-like surfaces is considered. The thicknesses (measured in the z-axis direction) at the first lens element and the second lens element are described by the following equations, respectively:

the thickness of each lens is given by:

the total thickness of the two lenses is

Where A and C are constants, x and y are lateral coordinates perpendicular to z to,

is the optical power. Here we assume that a is a positive constant. Obviously, the combined thickness of the two-element system is t-t 1+ t2-2C, which corresponds to a parallel plate. It can be shown that when the first element is moved by a displacement δ in the x-direction and the second element is moved by a displacement- δ in the x-direction, the combined thickness t has the parabolic form-2 Α δ (x2+ y2), simulating a condenser lens for positive displacements δ and a diverging lens for negative displacements δ. Where n is the refractive index of the lens material. Fig. 2 shows the effective overlap when each lens is moved by a displacement δ.

Assume that the gap between the two free contours is t and Δ is the distance between the two free contour surfaces in the active aperture D.

To avoid collisions during the movement of the lens, we condition that

Δ＞0，

That is, the lenses must not touch.

If we assume D > δ, we can establish the condition as:

zoom lenses in imaging systems (e.g. cameras) have two basic requirements: the focal length can be adjusted and the image plane can be fixed. To meet the two basic requirements, two pairs of alvarez-like lenses are required in the zoom lens system. As shown in fig. 2, we propose a new design by combining two pairs of alvarez lenses as a variable focus lens and a fixed focus lens. The two pairs of alvarez lenses can not only adjust the overall focal length of the system but also compensate for the change in position of the image plane.

Assuming an alvarez lens pair equivalent to a thin lens, in order to keep the image plane fixed during zooming, we have:

wherein f is₁Is the focal length of the first Alvarez lens pair, and f₂Is the focal length of the second Alvarez lens pair, k is a constant, d₁Is the distance between the two alvarez lens pairs.

The focal length of the whole system is:

where f is the focal length of the entire system and d₂Is the distance between the second alvarez lens pair and the fixed focus lens.

For a zoom lens (optical configuration as shown in fig. 3) used in a mobile phone, the system comprises two tunable lenses (tunable lens 1 and tunable lens 2) and a fixed focus lens set, with a stop aperture (aperture) located between tunable lens 1 and tunable lens 2. In order to keep the image plane at the same position during zooming, at wide angle the optical power of the adjustable lens 1 is positive and the optical power of the adjustable lens 2 is negative (as in fig. 3 (a)), at the telephoto end the optical power of the adjustable lens 1 is negative and the optical power of the adjustable lens 2 is positive (as in fig. 3 (b)). When zooming from wide angle to telephoto, the adjustable lens 1 changes its optical power range from positive to negative; on the other hand, the optical power range of the adjustable lens 2 changes from negative to positive.

For small size requirements of thickness of mobile phones and panels, the zoom optical system is optically bent at least once, as shown in fig. 4.

Optical power distribution

The optical power of the overall system is determined by the size of the image detector (usually CMOS or CCD) and the field angle.

Suppose that

And

are the power of the first and second sets, respectively, and d is the principal distance between the first and second sets. The combined optical power of the two lenses is:

where f is the focal length, θ is the field angle, and D is the diameter of the image circle.

Assuming that the zoom ratio is β, at the wide-angle end:

at the telephoto end:

wherein d is a distance between the first and second alvarez lens pairs.

The distance between the lens pairs can only be constrained to be between 4mm and 8mm in a limited space.

In order to meet the imaging requirements of the compact camera module, the optical power of the Alvarez lens 1 ranges from 0.3(1/mm) to-0.3 (1/mm) (the focal length ranges from 3.33mm to infinity and from infinity to-3.33 mm)

The optical power of the alvarez lens 2 ranges from-0.3 (1/mm) to 0.3(1/mm) (the focal length ranges from-3.33 mm to infinity and from infinity to 3.33 mm).

The set of ranges will satisfy the optical configuration of an optical zoom module adapted to fit in a camera phone.

Example (c): for an 1/4 inch CMOS, the FOV is 64 degrees and the zoom ratio is 3. At the wide-angle end, the focal length is:

at the telephoto end, the focal length is:

f_t＝f_w×β＝3.62×3＝10.86(mm)

the result in these ranges is that for small systems, the optimal gap between the alvarez lens pair can be determined. From fig. (6), for a focal length of 5mm, an aperture of 2mm and a material index of refraction of 1.5 times, the gap must be greater than 0.2mm to avoid interference during motion. For maximum optical power considered at an aperture size of 2.5mm (0.3 mm)^-1) We can determine the optimum range of gap between each pair of lenses as

0.2mm < gap <0.5mm

Reducing optical aberrations can be achieved by using higher order terms in the polynomial equation of the free form surface. By material configuration and selection, aberrations are reduced even more. One way to achieve this is to have a lens made of two materials with different abbe numbers (fig. 22). The lens may be made by separately injection molding two lenses and bonding them together during assembly. The relative proximity in the refractive indices of the two materials minimizes the optical error introduced at the interface. Another method is to first mold one side of the lens and then mold the other surface directly onto the pre-molded part. The lenses described herein may be made from optical quality cyclic olefin polymers (e.g., Zeonex), or may be made from polycarbonate or polystyrene, or low dispersion glass. It will also be appreciated from the teachings herein that in some embodiments, one material may be used for one lens and another material for a different lens, or for the prisms shown in fig. 4A-4B. It will also be appreciated that the lens may comprise two different materials bonded together, as discussed above in connection with fig. 22. Typically, the size of the lens used in the cell phone camera embodiment ranges from 4 to 10 millimeters, although other applications (e.g., security cameras, etc.) may be larger.

Referring next to fig. 23-28, an alternative embodiment of a lens system having an actuator suitable for use in a cell phone or other small application may be better understood. Referring to FIG. 23, it can be seen that the lens system or module includes a free-form lens assembly 2300 mated to a base lens assembly 2305. The base lens assembly includes a sensor mount 2310 on which the sensor is mounted. FPC cover 2320 is fitted over mating components 2300 and 2305, and metal cover 2315 is fitted over the top of the combination. An access opening or window may be provided in the cover 2315 and an opening for placement of a sensor may also be provided.

The free-form lens assembly can be understood in more detail from fig. 24, wherein the pairs of lenses 1 and 4 are mounted on a single shield and thereby form the lens group 2400. In some cases, the lens and the shield are molded in a uniform manner. Likewise, the second pair of lenses 2 and 3 are mounted together as a lens group 2405. The lens group is finally mounted in a movable relationship on a base 2410 by means of guide rod accommodators 2415, 2420 and 2425. Some aspects of the receiving member can be better understood from fig. 25, wherein the lens shield is in turn viewed as illustrating the relationship between the receiving member and the guide bar. More specifically, the guide rod accommodators 2415 and 2420 have holes through which one of the guide rods passes, and the accommodator 2425 includes a light chute through which the second guide rod passes.

The relationship between the receiving member and the guide bar may be viewed as a three point support for the lens shield which, although not required in all embodiments, helps to substantially reduce tilt, as discussed in more detail below. The guide bar is glued or otherwise rigidly fixed to the guide bar supports 2435 and 2440. The electrical coils 2445 on the base and associated printed circuit board match the permanent magnets mounted on the shields of the lens stacks 2400 and 2405. The magnet and coil interact to extend or retract the lens groups relative to each other in a direction substantially perpendicular to the optical axes of the pair, while maintaining sufficient alignment with prism 2455 through which light passes onward to the base lens. A metal band 2460 can be placed in the base such that the permanent magnets on the lens set interact with the band 2460 to provide a magnetic locking effect, as will be explained in more detail below in connection with fig. 27.

Fig. 26 illustrates a base lens in an exploded perspective view in accordance with an aspect of the present invention. Specifically, the base lens includes a base 2600, a base lens barrel 2605, one or more base lenses 2610, a prism and prism holder 2615, an optional IR filter 2620, a sensor bracket 2625, a sensor 2630, a magnet 2635 with matching electrical coils and a printed circuit board 2640, a base pair of guide rods that fit into a base lens holder 2650, and a guide rod bracket 2655. Similar to the free-form lens assemblies described above, when power is supplied to move the base lens barrel (in which at least some of the base lenses are mounted), the coils and magnets interact to focus light received from the free-form subassembly into an image on the sensor.

Referring next to fig. 27, a magnetic latch for use in conjunction with the free-form and base lens subassemblies described herein may be better understood. Specifically, metal strip 2455 is positioned on base 2410. When the magnet and the coil interact to move the lens group along the guide bar, the end of the lens group closest to the metal strip is biased downward to the metal strip due to the attractive force of the magnet. Instead, the opposite end of the lens stack is driven slightly upwards. If not addressed, these forces may result in sufficient tilt to cause unacceptable image distortion. However, by providing two guide rods (one on either side of the lens group) and three receptacles separated (two on one side and one on the other), the tilt can be significantly reduced in three dimensions. The above method enables the tilt of the free profile lens to be reduced to +/-0.2 degrees and the tilt of the base lens to +/-0.1 degrees, with the lenses and related elements having the dimensions described herein.

Conversely, in some aspects, the relevant problem is stiction: to provide a good user experience, the movement of the lens group along the guide bar must be smooth and reliable. At the same time, a very small gap with an aperture is required for the guide rod to pass through. To assist in this, the aperture through a portion of its opening is relieved (relief), as better shown in fig. 28, where small flat areas 2800 are provided on one or more sides. This provides a smaller contact area than the entire hole, allowing a reliable and smooth movement of the lens group or base lens along the guide rod.

Referring next to fig. 29A-29D, the techniques for improving manufacturability of rotationally asymmetric lenses according to the present invention may be better understood. In general, the active region of a single alvarez element does not include the entire lens region, as shown in fig. 29A. The unused area may result in a very steep profile that is difficult to manufacture and that may create interference between the lenses during lateral movement. It is therefore desirable to adjust these regions in a manner that eliminates potential interference between lenses and also ensures ease of manufacture.

One possible approach is to trace the perimeter of the active area and fill the unused area with a surface profile having a value closest to the perimeter. For example, one approach is to fill the surface profile with the same values along the x-axis as the perimeter values of the active area, as generally shown in fig. 29B.

Other steps may be taken to create a more manufacturable surface. In the above example, with compensation, the surface may still result in a very steep profile at the edge of the circle tangential to the axis. A related problem is that it is desirable to have a means of checking the alignment of the lenses during manufacture and during assembly. To solve both problems simultaneously, it is useful to find the lowest or highest point along the unused area and fill the rest of the area with this value. This will flatten the four corners of the lens area as shown in fig. 29C.

Further work may be done to aid in manufacturing. The transition between the active region and the compensation region may be smoothed in a linear or polynomial function that gradually changes. This facilitates removal of sharp changes in surface gradients that may present manufacturing challenges.

Other challenges posed by the use of free-form lenses include alignment and measurement difficulties due to the lack of an optical center for the free-form lens. A related challenge is the need to identify undesired rotation during assembly. These challenges can be overcome by molding the alignment features into the lens body and thus using the lens body or the shield as a lens reference. These characteristics (e.g., lens, grating lines, or slope (slope)) can then be measured optically or mechanically to assist in checking lens alignment.

Since the entire surface is contoured and compared to theoretical data to determine position, it is difficult to accurately position the free form lens along the Y-axis. One technique to overcome this is to create a flat (B) and a sloped (C) surface that can be contoured in a single scan, such as the design shown in fig. 30A. Additional sloped and flat reference areas may be molded with the lens, alongside the free form surface. Molding does not create a sharp intersection between the bevel and the flat surface, so the bevel and flat regions are contoured together. However, the theoretical location of intersection with points of all freeform surfaces along the Y-axis is known. The intersection point can be found by calculation by profiling the bevel and the plane.

Another variation is to map the X or Y axis position to the height of Z, again by using the tilt feature shown in fig. 30B. To determine the position of the freeform lens along the X-axis, the "E" of the feature is used. The Z-height of the bevel, when accurately measured, can be used to determine the position along the actual X-axis of the lens surface. Similarly, the "D" of a feature may be used to locate the position of the Y-axis. From both "E" and "D", the X-axis and Y-axis positions of the freeform surface can be inferred.

Fig. 30C and 30D show a comparison of the design profile and the measurement profile. In the measured profile, it is assumed that the measured points a1, a2, A3, a., An, B1, B2, B3,. the., coordinates of Bm are (Xa1, Ya1), (Xa2, Ya2), (Xa3, Ya3),. the., (Xan, Yan), (Xb1, Yb1), (Xb2, Yb2), (Xb3, Yb3),. the., (Xbm, Ybm)

Let equation y be k1x + B1 for segment a 'C' and equation y be k2x + B2 for segment B 'C'.

For line segment a 'C':

Ya1’＝k1Xa1；

Ya2’＝k1Xa2；

Ya3’＝k1Xa3；

…

Yan’＝k1Xan；

the form of the minimum error function is used to obtain the best fit line, such that K1 and b1 are determined by:

similarly, for line segment B' C:

Yb1’＝k2Xb1；

Yb2’＝k2Xb2；

Yb3’＝k2Xb3；

…

Ybm’＝k2Xbm；

k2 and b2 are determined by the following formula:

the tilt angle of the scanning trajectory is:

α＝arctan(k₂)

the bevel angle is:

θ'＝arctan(k₁)

thus, the coordinates of the intersection of line segments a 'C and B' C may be determined as:

referring next to fig. 31A-31D, in some embodiments, alignment may be assisted by fabricating optical features on the bezel or lens frame at the same time as the freeform lens is formed. The optical features may be lenses that are aligned using conventional methods. In this way, the limitation of having features on the free form surface that are not readily identifiable can be overcome. As shown in fig. 31A, optical features 3100 and 3105 (such as rotationally symmetric lenses, etc.) can be formed on the lens frames for free-form lenses 3110 and 3115, respectively. To align the free-form lenses, each frame may position at least one of the lenses in alignment with each other, and conventional alignment methods may be applied to the alignment. For example, centering of a rotationally symmetric lens may be accomplished by a laser beam aimed at finding the apex (apex) of the rotating lens. A plurality of such lenses (e.g., up to three) arranged at various locations of the lens frame may provide additional improvements in alignment. Even the use of only a single optical feature per lens frame or shield allows for the aligned assembly of multiple freeform lenses, including the alignment of configurations requiring optical path bending, as shown in fig. 31B, which illustrates the alignment of four freeform lenses by a single laser beam passing through the various optical features. For some systems, a more rudimentary, less effective alignment method may include only holes in the lens frame.

While the optical features assist in establishing a reference position for the lens, other reference positions may be useful in calibrating any position feedback sensors on the module in subsequent operations. These position feedback sensors may include hall sensors, capacitive sensors, piezoelectric effect sensors, and linear encoders. For any sensor, calibration is a necessary step to achieve high positioning accuracy. The calibration step entails the positioning of the actual position of the lens for the signals measured by the various sensors. For example, for a hall sensor, the lens frame may carry a magnet that, when moved with the frame, creates a changing magnetic field that is picked up by a stationary hall sensor mounted on the module housing. This changing magnetic field reflects the change in position of the lens frame.

Calibration allows the sensor to identify the magnetic field signal it should sense for the desired frame position. The input of the actual position needs to be obtained from an external device. The relative initial position between the frames may be determined by the alignment marks described previously. From these relative initial positions, the subsequent position of the lens frame can be obtained by using an external displacement measuring tool, such as a laser displacement sensor. In this way, the magnitude of the magnetic field collected by the hall sensor at various locations of the frame can be correlated to the position of the frame. One example of a measurement process is illustrated in fig. 31C and 31D. At the initial reference position, the hall sensor signal may be recorded. From the left figure, a laser displacement sensor can be used to measure a portion of the lens frame to obtain its position. By moving the frame to various positions as needed, the hall sensor readings for each position can be tabulated along with known position values.

The single lens alignment function on each frame allows alignment in the X, Y, Z axes and rotation in the X and Y axes. Only the Z-axis (with respect to the symmetry axis of the lens) cannot be determined. The position of the frames can be fully determined by using two lens alignment features in each frame. More lens alignment features may be added in a manner that is progressively less effective.

Each lens alignment feature may range from 0.1mm to 10mm depending on the implementation and application. In at least some cases, smaller lens sizes may be associated with smaller alignment features. Limitations of smaller lens sizes include the ease of focusing or collimating the laser beam and the amount of signal intensity that can be obtained being used effectively.

For a lens of 4mm diameter or diagonal, the maximum slope of the free form surface will be less than 60 degrees. As the diagonal of the lens becomes larger to 10mm, the slope of the desired profile may be reduced to less than 40 degrees.

Suitable image sensors may range in size from 1/2 "to 1/4" within a 10mmx40mmx40mm module package.

Free-form lenses that translate transverse to the optical axis provide a compact way to achieve optical zoom and other features. To achieve optical zoom, the movement of the lenses must be bi-directional and synchronized. One factor in achieving a low cost solution is the ability to reduce the number of actuators in the system. One way to achieve this is to reduce the number of actuators, connecting multiple lenses together.

Assume that the optical system includes two lenses, one of which is G1 (alvarez lens pair 1) and the other of which is G2 (alvarez lens pair 2).

Optical power of the whole system

The method comprises the following steps:

the working distance L is:

assuming that the traveling range of the Alvarez lens from the wide angle to the telephoto is 2mm, at the wide angle end, the optical powers of the two lenses are

And

at the telephoto end, the optical powers of the two lenses are

And

at random positions, the optical power of the two lenses is

And

at the wide-angle end, the working distance is:

at the telephoto end, the working distance is:

at random positions:

at random positions, the optical power of each lens pair is:

while

The optical powers of the lens groups G1 and G2 at the wide-angle end and the telephoto end, respectively.

If we fix the free form 1 and the free form 4 together and the free form 2 and the free form 3 together during zooming, this means we have to keep Δ during zooming₁＝Δ₂＝Δ；

If we want to do continuous zoom while keeping working distance, as equation (8):

L_w＝L_T＝L_r (8)

the above equation is valid only when Δ ═ 0 or Δ ═ 2.

The actuator system can be simplified by connecting the lenses in pairs. This may result in an optical zoom configuration with two discrete zoom points. This is the simplest configuration that can be used for the optical zoom lens.

In some embodiments of the present invention, particularly those providing optical power greater than 3x, it is desirable to be able to move each of the four lens elements comprising the two alvarez lens pairs separately. While this requires additional complexity, as shown in the discussion above, in some cases, the additional complexity is a reasonable tradeoff for enhanced performance. Referring next to fig. 32D-34B, various actuators that effect independent movement of the lenses are shown. Such actuators must be capable of providing one or more of the following features: (a) lenses 1 and 2 move the same distance in different directions, while lenses 3 and 4 move the same distance in different directions as each other, but different from lenses 1 and 2. (b) Lenses 1, 2, 3 and 4 all move different distances, while two move in the same direction as each other and the other two move in the opposite direction to the first two. Desirable design features are that these actuators must meet form factor requirements for a Z height of less than 6.5mm, they must move the lens at least 3mm with a positional accuracy of 5 μm, they must have a sufficient number of stops to provide a good user experience, they must be cost effective, they cannot use excessive power, and they must be easy to manufacture and assemble.

32D-32E illustrate a rotary cam actuator that can move each of four lenses a different distance, with two moving in opposite directions from the other two. Fig. 33A-33B illustrate a linear motor driving a cam profile to achieve the same result, while fig. 34A and 34B illustrate an embodiment of a gear and friction wheel that is also capable of driving multiple lenses to move different distances, which is also some lenses moving in one direction and the same number of lenses moving in reverse.

The design manufactured as described above achieves the following characteristics:

parameter(s)	Free form lens	Base lens
			Surface Profile (PV)	<0.5μm	<0.3μm
Surface eccentricity (X, Y)	+/-2μm	+/-2μm
			Surface inclination	+/-0.02deg	+/-0.02deg
Eccentricity between elements	+/-5μm	+/-5μm
			Thickness of	+/-1μm	+/-1μm
Element tilting	+/-0.2deg	+/-0.1deg
			Index of refraction	+/-0.00025	+/-0.00025
Abbe%	+/-0.25	+/-0.25

Frame tilt (L-shape): 0.1 degree

Sub-module assembly: 5 μm

Prism (45deg angle): +/-0.02 degree

The prism assembly is inclined: 0.1 degree

Having now fully described several embodiments of the invention, it will be appreciated by those skilled in the art that many alternatives and equivalents may be made thereto without departing from the scope of the invention. Accordingly, the invention is not to be limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims (10)

1. An optical zoom lens system, comprising:

at least one micro-actuator configured to move one or more optical elements,

at least four optical elements for causing optical power variations of the system, each of the at least four optical elements configured for passing an optical signal along an optical signal travel path, each of the at least four optical elements comprising at least one freeform surface, each of the at least four optical elements supported by an arm having a lens frame,

wherein at least four optical elements are positioned in a pair-wise configuration such that a first optical element and a second optical element, each mounted in its respective lens frame, form a first pair and a third optical element and a fourth optical element, each mounted in a respective lens frame, form a second pair, each pair being relatively movable relative to an associated first guide frame and second guide frame, by movement of at least one of the respective lens frames, in a direction generally transverse to the optical signal path, to cause a change in optical power of the system, the first guide frame being associated with the first pair, the second guide frame being associated with the second pair,

wherein the optical zoom lens system further comprises a base lens positioned along the optical signal travel path and configured to assist in focusing.

2. The optical zoom lens system of claim 1, wherein the at least one micro-actuator is at least two micro-actuators.

3. The optical zoom lens system of claim 1, wherein one of the at least two microactuators causes relative movement of the first pair and another of the at least two microactuators causes relative movement of the second pair.

4. The optical zoom lens system of claim 1, wherein the at least one micro-actuator is four micro-actuators, each micro-actuator configured to move with the associated lens frame relative to the associated guide frame.

5. The optical zoom lens system of claim 1, wherein the base lens comprises at least one rotationally symmetric lens element.

6. The optical zoom lens system of claim 1, wherein the at least one micro-actuator is a voice coil motor.

7. The optical zoom lens system of claim 1, wherein the first pair comprises prisms.

8. The optical zoom lens system of claim 6, wherein the lens frame of each of the at least four optical elements has a coil of the voice coil motor associated therewith.

9. The optical zoom lens system of claim 8, wherein the coil is fixed to the associated lens frame.

10. The optical zoom lens system of claim 1, configured to provide an image to a sensor, and further configured to respond to a signal from an image signal processor by adjusting a focus of the lens system.

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