WO2009100511A1

WO2009100511A1 - Planar resonant scanner with highly coupled inductive action

Info

Publication number: WO2009100511A1
Application number: PCT/BR2009/000035
Authority: WO
Inventors: Luiz Claudio Marangoni De Oliveira; Luiz Otávio Saraiva FERREIRA
Original assignee: Universidade Estadual De Campinas-Unicamp
Priority date: 2008-02-12
Filing date: 2009-02-12
Publication date: 2009-08-20
Also published as: BRPI0801780A2; BRPI0801780B1

Abstract

The object of the present invention comprises a planar base of material with good mechanical properties that is suspended by torsion bars (2) anchored on a panel (4) made of the same material, forming a single part. This base has a mirror (3) to reflect the light beam and a hole (1 ), which defines a conductive spiral and that is traversed by a ferromagnetic circuit. The combination formed by the mirror (3) and spiral is called a rotor (1 ) or armature and is moved by means of Lorentz electro-magnetic forces. Said forces are generated by the interaction between an electric current induced on the spiral by an alterate magnetic field that runs through the ferromagnetic circuit and a continuous magnetic field and parallel to the spiral, generated by a set of fixed magnets. The ferromagnetic circuit confines the magnetic excitation flow and makes most of this flow pass through the spiral of the rotor (1 ), maximizing the current induced, which is referred to herein as high coupling. The counter-position between the torque induced on the spool and the restoring torque, due to the spring force of the torsion bars (2), produces the oscillating movement of the rotor (1 ). By exciting the device in its mechanical resonance frequency, the maximum deflection amplitude of the rotor (1) is achieved.

Description

Specification of Patent of Invention

PLANAR RESONANT SCANNER WITH HIGHLY COUPLED INDUCTIVE ACTION

Technical Field Scanners are devices used for precise and efficient control of the direction of propagation of a light beam, usually laser, used in various optical equipments. They can be found in all sorts of equipments, such as laser printers or supermarket bar code readers, and also in highly sophisticated equipment, such as confocal microscopes used for three-dimensional inspection and measurement of biological and industrial samples, or retinal displays, used as military equipment to assist the vision of soldiers.

The direction of propagation of a light beam can be altered in many ways, reflecting the light onto one or more mirrored surfaces being the most widely used form.

Background and Prior Art

The vast majority of scanners currently used are electro-mechanical devices comprised of two main parts: the mirrors, which should reflect the light beam; and the drive mechanism, which should move these mirrors to position the light beam.

Polygonal scanners, also called rotary mirrors, position the light beam by rotating a mirrored polygon coupled to a shaft of a motor that turns in uniform speed. The reflected beam has uniform movement and a single direction of deflection. Such devices were the first to be developed and have the advantage of obtaining high deflection angles. Their weak points are the high power consumption and space occupied, impossibility of randomly positioning the beam, mechanical complexity, and impossibility of batch manufacturing, meaning its cost is relatively high.

The galvanometric scanner, also called "galvano scanner", was initially developed for graphic applications characterized by the need for random positioning of the light beam. This kind of device uses a motor with limited shaft movement to position a single mirror that should reflect the light beam. An oscillating movement of the light beam arises from the interaction between the excitation force, generated by the motor, and the restoring force, produced by an elastic suspension, and which counter-poses the excitation force of the motor, forming a second order electro-mechanical system. This kind of scanner can operate in the mechanical resonance frequency of the structure, being called resonant scanner, or at an interval of frequencies below its resonance frequency. The resonant device is highly rigid, has low rotor inertia and, benefiting from the resonance phenomenon, has high deflection angles from small torque. Non- resonant devices, however, need high torques in order to obtain high deflection angles. Consequently, its power consumption is greater than that of the resonant devices. The advantages of the non-resonant devices are: the possibility of random positioning with high deflection angle of the light beam and its operation at a wide interval of frequencies. The high power consumption and space occupied, low operating frequencies, its mechanical complexity and the impossibility of batch manufacturing are the main drawbacks of this device in relation to the device of the present invention.

With the development of microelectromechanical systems or MEMS, the possibility arose of developing electrical machines using batch manufacturing techniques thus far used in the electronics industry. The first micromechanical scanner was proposed by Petersen in 1980 (Petersen, K. E., "Silicon Torsional Scanning Mirror", IBM J. Res. Develop., 1980, 24, 631-637). Chemically machined in silicon, the mirror with 2.5 mm in length by 2.5 mm in width, was moved by the action of electrostatic forces. The low efficiency of the electrostatic drive for devices of millimetric order provided deflection angles of at least 1 peak- to-peak in resonance, with drive voltages close on 400V. Although it has not been used industrially, Petersen's electrostatic scanner demonstrated the viability of manufacturing scanners using the same planar manufacturing technology used in microelectronics. With the evolution of this technology, the 1990s witnessed the arrival of micromechanical scanners driven by electromagnetic forces, or galvanometric microscanners. In devices of the order of some millimeters, such as microscanners, electromagnetic drive is more efficient than electrostatic. Nevertheless, magnets should be added outside the system in order to produce electromagnetic forces capable of moving the mirror, which can be achieved by a suitable packaging project for the device. Galvanometric microscanners use the same principle as galvanometric scanners: the oscillating movement due to the counter-position between an excitation force and a restoring force, in a second order system. In microscanners, the excitation force is produced by the interaction between an external magnetic field, produced by magnets, and an electric current injected in an armature recorded on the same base that contains the mirror, and which is suspended by one or more torsion bars, responsible for generating restoring forces. Microscanners operate at the mechanical resonance frequency of the structure in order to achieve usable deflection angles of the beam. The main advantages of these devices include: reduced volume, low power consumption, the possibility of batch manufacturing using processes derived from microelectronics, greater operating frequencies than large scale similar products with compatible deflection angles. The presence of tracks on the torsion bars of the scanner makes this device subject to failures due to the effect of fatigue of the tracks. Another drawback is the need to record and subsequently solder a spool on the base that forms the rotor, which adds at least two steps to the planar manufacturing process. Another negative aspect is the low resistance of the device to impacts, due to the use of silicon as structural material. To solve the problem of fatigue of the tracks on the torsion bars and to simplify the manufacturing process, the end of the 1990s saw the development of microscanners driven by induction, or induction microscanners (Ferreira, L. O. S., "Microscanner de Silfcio", doctorate thesis defended at the Faculty of Electrical Engineering and Computing of UNICAMP, Campinas, SP, 1994). The movement of the mirror in these devices occurs by the same principles as the galvanometric devices: the opposition between an excitation force, produced by the drive circuit, and a restoring force caused by the torsion bars. The excitation force arises from the interaction between an electric current induced in the armature by an electromagnetic field variant in time and an electromagnetic field invariant and parallel to the armature produced by fixed magnets. The electro-magnetic forces induced are called Lorentz forces. Induction scanners are structurally simpler than galvanometric scanners due to the fact that the spool which makes up the armature does not need to be powered by an external current. Accordingly, the need for tracks on the torsion bars is eliminated, and consequently the associated problem of fatigue of the tracks. However, the need arises to produce a magnetic field variant in time and perpendicular to the armature spool. This demands a ferromagnetic circuit outside the device. The intensity of the Lorentz forces induced will be directly proportional to the coupling of this alternate magnetic field with the armature spool. In the first induction devices manufactured this coupling was made by air, such that the field was spread, and only a small part was used to produce the Lorentz forces. With this, deflection angles were achieved typical in resonance of 18 peak-to-peak for a frequency of 1311Hz, with a drive power of about 4OW (Barbaroto, P. R. "Projeto, Microfabricacao e Caracterizacao de Defletor de Luz de Silϊcio Acionado por Inducao", master's degree dissertation defended at the Faculty of Electrical Engineering and Computing of UNICAMP, Campinas, SP₁ 2002). The very high consumption of power was due to the inefficient coupling between the excitation field and the armature. Due to this characteristic, said devices were called weakly coupled induction scanners.

The present invention is designed to remedy the problem of weak coupling between the excitation magnetic field and the armature spool. The geometry of the rotor was altered by the addition of a hole which should be traversed by the ferromagnetic circuit. By this mechanism, most of the excitation alternate field is confined in the magnetic circuit and traverses the armature spool, meaning that the Lorentz forces generated are maximized. Said mechanism was named high coupling and it is similar to the mechanism developed by Montagu in 1985 (Montagu, J., "Resonant actuator for optical scanning "Patent # US4502752, USA, 1985), with the difference that in the object of the present invention the scanner is entirely planar, whereas in Montagu's invention the armature spool is perpendicular to the mirror in a complex three-dimensional structure. In the present invention besides silicon, used thus far as structural material in microscanners, metals were used such as, for example, phosphor bronze, or polymeric materials. The metal device made it unnecessary to add the armature spool to the scanner, which was made during an additional manufacturing step, being made in a single chemical machining process. If the metal has good electrical properties, the spool armature is made of the structural material itself. In a subsequent step, the mirror is stuck to the surface of the rotor.

The polymer device can be made, for example, of phenolite, polyamide or any other material with good mechanical properties. The polymer can be machined or made in a suitable geometry, after which it should receive the conductor spiral (if the polymer does not have suitable conductivity) and the mirror.

With these measures, a low-cost, planar device was achieved, that could be made in batches and with an operating frequency four times greater and with double the deflection angle of the galvanometric devices and similar inductions. The problem of low resistance to the impacts was also substantially minimized by the choice of the structural material.

Summary of the Invention

The object of the present invention consists of a planar resonant scanner with highly coupled inductive action, which is a device comprised of a planar base suspended by torsion bars (2) anchored to a support made of the same material, forming a single part. The planar base or rotor (1) has a mirror (3), a spiral and a hole through which the magnetic circuit passes, made, for example, of ferrite, which confines the magnetic excitation field and means most of the magnetic flow traverses the spool (6), maximizing the Lorentz forces that act upon the rotor (1). The scanner should operate at the mechanical resonance frequency of the structure. The device enables deflection angles typical of 20° peak-to-peak to be obtained in the resonance and operating frequencies of 4kHz or above. The absence of power tracks on the torsion bars (2) and the planar geometry allow its batch manufacturing and the use of low-cost manufacturing materials and processes.

Brief Description of the Figures

Figure 1 depicts a planar inductive scanner in phosphor bronze;

Figure 2 depicts the high coupling between armature spool (9) and actuation (6); Figure 3 presents an electro-mechanical model of the scanner;

Figure 4 presents a simulation by finite elements of the torsional vibration mode;

Figure 5 illustrates a batch of scanners made of phosphor bronze by chemical machining; Figure 6 illustrates the highly coupled planar resonant scanner assembled with reflective surface made of Si (10);

Figure 7 presents a frequency response of the device, showing an optical deflection angle of 21.7° in 3677 Hz₁ where the scanner was excited with a sine voltage of 13Vpp; Figure 8 shows a scanner with three rotors (1 ', 1 " and 1 '"); and

Figure 9 illustrates a planar inductive scanner planar with movement in directions X (2', T and 9') and Y.(2", 7" and 9").

Detailed Description of the Invention Optical scanners are used to control the direction of the propagation of a light beam. They are used in laser printers, optical microscopes, bar code readers, image projectors, among other applications. Most optical scanners comprise a reflector surface which moves and deflects the light beam.

The planar resonant scanner with highly coupled inductive action comprises a rotor (1), suspension system and fixture panel (4), manufactured in a single part, and a stator (7). The complete combination is enclosed in a support responsible for aligning the assembly and for fixing an electrical connector. The device, manufactured to operate at 3677Hz and optical deflection angle of 21.7° pp, typically has the dimensions 40mm x 20mm x 20 mm.

The single part that contains the rotor (1), the suspension and the fixture panel (4) is shown in FIGURE 1. The rotor (1) is suspended by two torsion bars (2) and comprises two parts isolated by a third torsion bar (2), in a system called double rotor. In this system, the mirror (3), responsible for deflecting the light, is isolated from the armature spool (9), where the Lorentz forces that move the combination are generated. The separation of functions provides a more streamlined design for these components.

An armature spool (9) is formed by a single short-circuited spiral, defined by the geometry of the device and made of the same material, having a central hole that permits the passage of the ferromagnetic stator (7) for high coupling to occur. The stator (7) comprises a ferromagnetic circuit made with pre-molded ferrite cores in an E-I format, on which a spool is wrapped with about 200 spirals, called actuation spool (6). In FIGURE 2, the stator (7) used to drive the highly coupled scanner is depicted. The magnetic field generated in the actuation spool (6) by applying a typical alternate voltage of 10V is confined in the ferromagnetic circuit and most of it traverses the armature spool (9) perpendicularly. The current induced in the armature (9) should interact with a continuous magnetic field generated by one or more pairs of permanent magnets (8), for example, NeFeB, which are fixed on the stator (7) so as to generate a field parallel to the surface of the spool, FIGURE 2. The confinement of the magnetic excitation field in a ferromagnetic circuit that traverses perpendicularly an armature spool (9) and maximizes the voltage induced in the armature (9) is called high coupling. The torque induced in the armature (9) by the Lorentz forces is in counter-position to the restoring torque generated by the torsion bars (2), forming a second order system. The excitation of the device with an AC voltage in the frequency of one of the torsional mechanical modes of vibrating the rotor (1 ) makes the oscillation in the system maximized by the effect of resonance. The invention is designed such that the desired operating frequency is the frequency of one of the torsional mechanical modes of vibrating the structure. The electro-mechanical model of the device is shown in FIGURE 3. This model includes the electric and mechanical characteristics of the device and foresees that the deflection amplitude of the device is given by Equation 1 , shown below:

θ _device (S) = [- B_DCK _Θ3A²] V₆ (S)

[ N_e R_aJ_m2 ] (As⁴ + Bs³ + Cs² + Ds + E)

Equation 1 - Deflection amplitude of the device based on the operating frequency. B_Dc is the magnetic field generated by the permanent magnets (8), A is the area of the armature spool (9) perpendicular to field AC, N_e is the number of spirals of the excitation spool, J_m2 is the momentum of inertia of the mirror (3), V_e is the excitation voltage, and A, B, C, D and E are mechanical constants of the model.

The vibration modes of the device are foreseen by a structural model by finite elements, shown in FIGURE 4. By way of this model, it is possible to predict the torsional and flective vibration modes of the structure and its geometry can be altered such that the torsional modes occur in the desired operating frequency for the scanner.

A whole part that contains the rotor (1), suspension and fixture panel (4), FIGURE 1, is made of phosphor bronze, and can also be made of Si, polymer, composites and other non-ferrous materials with good mechanical properties. Manufacturing this part with materials that conduct well, such as phosphor bronze, simplifies the process by eliminating the need to add the armature spool (9) by an additional process of chemical deposition or adhesion. This part has the dimensions of 34mm x 24mm and is 0.7mm thick and was manufactured by chemical machining of the phosphor bronze. FIGURE 5 shows a batch of these parts manufactured by chemical machining. Other processes, such as laser cutting, could be used for manufacturing these parts, yet the process of chemical machining eliminates the need of a subsequent thermal treatment of the structure to remove the residual voltage resulting from laser cutting, for example. An aluminum mirror (3) placed on a glass slide was stuck on the rotor (1) of the structure. The stator (7) is formed by a ferrite core, standard size, of the E-I type, whose central arm has an area of 5mm x 5mm. The excitation spool was positioned on this arm, rolled in a standard support for the ferrite core and with 200 rounds of copper wire 24 AWG. The stator (7) was positioned and fixed by screws M4 inside a support made of acrylic, having the dimensions of 40mm x 20mm x 20mm. The part in phosphor bronze is positioned such that the armature spool (9) is traversed by the central arm of the E-I ferrite core, and is fixed on the acrylic support with screws M3. The ferrite core was finely aligned to the armature (9) and the assembly was fixed by screws M4. At this point, the permanent NeFeB magnets (8) were positioned and fixed by magnetic attraction on the ferrite core such that the field generated was parallel to the armature (9). The assembly was concluded by positioning component I of the ferrite core, which was positioned and fixed by magnetic attraction, and by soldering the wires of the excitation spool in a connector DB9 which was fixed on the support of the scanner. FIGURE 6 shows the assembled device. FIGURE 7 shows the frequency response curves for the manufactured device wherein it is possible to verify the occurrence of an optical deflection angle of 21.7° pp in the operating frequency of 3677 Hz. The monolithic part that forms the device could be made of another material with good mechanical properties like Si, or any other material that is not ferromagnetic. For devices made of materials that are poor conductors of electricity, such as Si, phenolite or polyamide, an additional process would be necessary to deposit the aluminum or other metal to form the armature spool (9). In the case of Si, the manufacturing would be by chemical machining. The use of silicon blades polished on both sides (DSP - Double Side Polished), would eliminate the step of sticking the mirror (3), since the Si itself would be the mirror (3). The performance of the device could be improved if structures were made to alleviate the mass of the mirror (3) made of Si. Said structures could be honeycomb-shaped, or any other shape and could be made by physio-chemical corrosion of Si. The double-rotor structure could be replaced by a structure with a single rotor, in which the maximum mechanical coupling between the movement of the spool (6) and the mirror (3) occurs.

The structure of the rotor (1) could be constructed with 3 or more structures (triple-rotor, quadruple-rotor, etc.) which could have separate drives. A rotor with the mirror (8) would be on the center of the mobile structure and would be driven by the torque resulting from a composition of various drives, FIGURE 8.

Greater deflection angles of the mirror (3) can thus be achieved. Other wave forms, except sine, could be obtained from the composition of the torque wave generated by each actuator.

For devices made of hard materials, such as phosphor bronze, the mirror

(3) could be made of chemically polishing the surface of the material so it would have mirror-like quality. This would be the preferred process, as it would eliminate the effects of the mass-spring system formed by a body stuck to a mobile surface.

Devices made of phenolite could incorporate in their rotor (1) the position detecting system formed by photoemissions and photoreceptors which would be soldered in printed circuit tracks previously established in the material. In the same way, the electronic circuits could be incorporated to control and drive the scanner.

The ferromagnetic drive circuit (7) could be of the U-I type, which would reduce the volume of the device and its magnetic reluctance, which would increase the performance of the device.

The device that deflects the beam in directions X and Y could be created if two actuators were connected perpendicularly, as shown in FIGURE 9. The bidirectional induction scanner would have an armature (9¹) and a mirror rotor (3) which would carry out the movement in direction X and the support frame of this device would be suspended by a second set of torsion bars (2") subject to a torque in direction Y, generated in the armature spool (9) of a second rotor. The composition of the movements would permit the deflection of the beam in directions X and Y. The actuation in direction Y could be, for example, highly inductive or weakly coupled, electrostatic, galvanometric, piezoelectric, or any other producing sufficient torque to rotate the structure.

Claims

ClaimsPLANAR RESONANT SCANNER WITH HIGHLY COUPLED INDUCTIVE ACTION

1. Planar resonant scanner with highly coupled inductive action, CHARACTERIZED by comprising a rotor (1), planar base suspended by torsion bars (2), a suspension system and a fixture panel (4), manufactured in a single part, and a ferromagnetic stator (7).

2. Scanner, according to claim 1 , CHARACTERIZED by adding a support responsible for aligning the assembly and for fixing an electrical connector.

3. Scanner, according to claims 1 and 2, CHARACTERIZED wherein the rotor is suspended by two torsion bars (2) and comprises a third torsion bar (2), in a system called double rotor, wherein the mirror (3) and the armature spool (9) are isolated.

4. Scanner, according to claim 3, CHARACTERIZED wherein the spool is formed by a single short-circuited spiral, defined by the geometry of the device and in the same material, with a central hole that permits the passage of the ferromagnetic stator (7).

5. Scanner, according to claim 4, CHARACTERIZED wherein the stator comprises a magnetic circuit manufactured with pre-molded ferrite cores in the E- I shape, on which a spool is rolled having around 200 spirals, called actuation spool (6).

6. Scanner, according to claim 3, CHARACTERIZED wherein the current induced in the armature should interact with a continuous magnetic field generated by one or more pairs of permanent magnets (8) that are fixed to the stator (7) so as to generate a parallel field to the surface of the spool.

7. Scanner, according to claim 6, CHARACTERIZED wherein the magnets (8) are NeFeB.

8. Scanner, according to claims 1 to 7, CHARACTERIZED by operating at the frequency of one of the mechanical torsional modes of vibration of the structure, which are foreseen by a structural model by finite elements.

9. Scanner, according to claim 1, CHARACTERIZED wherein the whole part containing the rotor (1), suspension and fixture panel (4), is made of phosphor bronze.

10. Scanner, according to claim 9, CHARACTERIZED wherein said part, the mirror (3) is made by chemical polishing of the surface of the material.

11. Scanner, according to claim 1, CHARACTERIZED wherein the whole part containing the rotor (1), suspension and fixture panel (4), is manufactured alternatively of Si, polymer composites and other non-ferrous materials with good mechanical properties.

12. Scanner, according to claim 1 , CHARACTERIZED wherein the part has the dimensions 34 mm x 24 mm and is 0.7 mm in width.

13. Scanner, according to claims 9 and 11, CHARACTERIZED wherein the part is manufactured by way of chemical machining of the material.

14. Scanner, according to claim 3, CHARACTERIZED wherein the double-rotor structure (1) may alternatively be substituted by a structure with a single rotor (1).

15. Scanner, according to claim 3, CHARACTERIZED wherein the structure of the rotor (1) may alternatively be made of 3 or more structures, that can have separate drives, wherein a rotor (1) with the mirror (3) is located in the center of the mobile structure and driven by the torque resulting from the composition of various drives.

16. Scanner, according to claims 1 to 15, CHARACTERIZED by enabling the achievement of typical deflection angles of 20° peak-to-peak in the resonance and operating frequencies of 4 kHz or greater.

17. Scanner, according to claims 1 to 15, CHARACTERIZED wherein the electromagnetic model of the scanner comprises a deflection amplitude given by the equation 1 :

θ _dβvice (s) = [- B_DCK _Θ3A²] V_e (s)

[ N_β R_aJ_m2 ] (As⁴ + Bs³ + Cs² + Ds + E)

wherein B_Dc is the magnetic field generated by the permanent magnets (8), A is the area of the armature spool (9) perpendicular to field AC, N_e is the number of spirals of the excitation spool (6), J_m2 is the momentum of inertia of the mirror (3), V_e is the excitation voltage, and A, B, C, D and E are mechanical constants of the model.