WO2016056003A1

WO2016056003A1 - Device and method for position control using two independently controllable electromagnetic drive arrangements

Info

Publication number: WO2016056003A1
Application number: PCT/IL2015/050996
Authority: WO
Inventors: Yaron Zimmerman
Original assignee: Yaron Zimmerman
Priority date: 2014-10-07
Filing date: 2015-10-07
Publication date: 2016-04-14

Abstract

A device for position control includes independently controllable first and second electromagnetic drive arrangements in mechanical driving relationship with an object. A sensor arrangement 'is functionally associated with the object for determining position of the object. A control unit is associated with the sensor arrangement and the first and second electromagnetic drive arrangements. The control unit actuates the first electromagnetic drive arrangement to provide a force profile to move the object in an advancing direction towards a target position. The control unit actuates the second electromagnetic drive arrangement to provide a force profile which includes at least one component of force resistive to movement of the object in the advancing direction. The at least one component of force varies as a direct function of position relative to the target position over a range of positions including the target position.

Description

Device and Method for Position Control Using Two Independently

Controllable Electromagnetic Drive Arrangements

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to position control devices.

In many industrial applications, devices for position control are used to move devices and objects to positions where they can perform a desired function. This is particularly true when using an XY table for precision controlled automated movement. For example, in semiconductor analysis processes, an XY table is used to move a semiconductor device, such as, for example a wafer, to be analyzed at specific points of the device. This application typically requires linear motion strokes in the range of 10 micrometers (μπι) - 500 millimeters (mm). The convergence distance for such stroke lengths is typically in the range of 5 nanometers (nm) - 10 μm. In order to enable such stroke lengths with nanometric precision, a motion system using direct drive linear brushless motors are typically used. However, the settling time for such systems with a 5 nanometers (nm) - 10 μm window is slow. Alternatively, motion systems using linear voice coil motors can provide a faster settling time, but cannot provide the required stroke length. Similarly, motions systems using springs can provide fast and accurate convergence, but cannot provide the required stroke length.

SUMMARY OF THE INVENTION

The present invention is a device and method for providing a functionality for position control using two independently controllable electromagnetic drive arrangements. According to the teachings of an embodiment of the present invention there is provided, a device for position control comprising: (a) first and second electromagnetic drive arrangements in mechanical chiving relationship with an object, the electromagnetic drive arrangements being independently controllable; (b) a sensor arrangement functionally associated with the object for determining position of the object; and (c) a control unit associated with the sensor arrangement and the first and second electromagnetic drive arrangements, the control unit configured to actuate the first electromagnetic drive arrangement to provide a force profile to move the object in an advancing direction towards a target position, the control unit further configured to actuate the second electromagnetic drive arrangement to provide a force profile including at least one component of force resistive to movement of the object in the advancing direction by the first electromagnetic drive arrangement, the at least one component of force varying as a direct function of position relative to the target position over a range of positions including tiie target position,

According to a further feature of an embodiment of the present invention, the function of position is a linear function.

According to a further feature of an embodiment of the present invention, the function of position is a non-linear function.

According to a further feature of an embodiment of the present invention, the force profile provided by the second electromagnetic drive arrangement further includes at least one component of force varymg as a function of the velocity of the object.

According to a further feature of an embodiment of the present invention, the movement in the advancing direction is linear movement.

According to a further feature of an embodiment of the present invention, the at least one component of force and the force profile provided by the first electromagnetic drive arrangement are substantially opposing forces.

According to a further feature of an embodiment of the present invention, the movement in the advancing direction is angular movement.

According to a further feature of an embodiment of the present invention, the object includes a movable table. According to a further feature of an embodiment of the present invention, the function of position is a monotonia function of position.

According to a further feature of an embodiment of the present invention, the first and second electromagnetic drive arrangements are motors.

According to a further feature of an embodiment of the present invention, the first and second motors are linear motors.

According to a further feature of an embodiment of the present invention, the first and second electromagnetic drive arrangements are separate windings of a single motor.

According to a further feature of an embodiment of the present invention, the motor is a linear motor.

According to a further feature of an embodiment of the present invention, the device for position control further comprises: (a) an arrangement of permanent magnets for providing the mechanical driving relationship of the windings with the object; and (b) a sensor configured for determining position of the associated electromagnets relative to the arrangement of permanent magnets, each of the windings is associated with an electromagnet.

According to a further feature of an embodiment of the present invention, the control unit includes a feedback loop for providing a control signal to control the at least one component of force.

According to a further feature of an embodiment of the present invention, the feedback loop includes a controller with at least one adjustable gain.

According to a further feature of an embodiment of the present invention, the controller includes at least one component for providing derivative control of an input signal.

According to a further feature of an embodiment of the present invention, the controller includes at least one component for providing proportional control of an input signal.

According to a further feature of an embodiment of the present invention, the feedback loop includes a first-order low pass filter.

According to a further feature of an embodiment of the present invention, the control unit is further configured to actuate the second electromagnetic drive arrangement to provide a force profile to move the object in the advancing direction, and the device is operable in a first mode, in which the force profile provided by the second electromagnetic drive arrangement moves the object in the advancing direction, and a second mode, in which the force profile provided by the second electromagnetic drive arrangement is resistive to movement of the object in the advancing direction by the first electromagnetic drive arrangement.

According to a further feature of an embodiment of the present invention, the change in operation from the first mode to the second mode is based on the position of the object.

According to a further feature of an embodiment of the present invention, the change in operation from the first mode to the second mode is based on the velocity of the object.

According to a further feature of an embodiment of the present invention, the sensor arrangement includes a position sensor,

According to a further feature of an embodiment of the present invention, the sensor arrangement includes an acceleration sensor.

According to a further feature of an embodiment of the present invention, the sensor arrangement includes a velocity sensor.

According to a further feature of an embodiment of the present invention, the control unit is further configured to receive a target position as an input, and the control unit is further configured to actuate the first electromagnetic drive arrangement to provide the force profile to move the object towards the input target position.

According to a further feature of an embodiment of the present invention, at least one of the first and second electromagnetic drive arrangements travels with the object as the object moves towards the target position.

According to a further feature of an embodiment of the present invention, at least one of the first and second electromagnetic drive arrangements remains in a fixed position as the object moves towards the target position.

According to a further feature of an embodiment of the present invention, the control unit comprises at least one processor and a data storage medium. There is also provided according to the teachings of an embodiment of the present invention there is provided, a method of position control comprising: (a) actuating a First electromagnetic drive arrangement using a controller to apply a force on an object to move the. object in an advancing direction towards a target position; (b) detecting a parameter of the object through a parameter sensor for providing a signal to control a second electromagnetic drive arrangement; and (c) controlling the second electromagnetic drive arrangement according to the signal to provide a force profile including at least one component, of force resistive to movement in the advancing direction,

According to a further feature of an embodiment of the present invention, the control of the second electromagnetic drive arrangement is provided by a feedback loop having at least one adjustable gain, and the method of position control further comprises: (a) controlling a rate of convergence of the object towards the target position by adjusting the at least one gain,

According to a further feature of an embodiment of the present invention, the method of position control further comprises: (a) actuating the second electromagnetic drive arrangement to apply a force on. the object to move the object in the advancing direction towards the target position,

BRIEF DESCRIPTION OF THE DRA WINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a device for position control according to an embodiment of the invention;

FIG. 2 is a block diagram of a control unit associated with components of a position control device according to an embodiment of the invention;

FIG. 3 is a block diagram including a control circuit according to an embodiment of the invention;

FIG. 4 is a diagram of the settling time of a device for position control according to an embodiment of the present invention; FIG. 5 is an isometric view of a device for position control configured for linear motion according to an embodiment, of the invention;

FIG. 6 is a top view of the device of FIG, 5;

FIG. 7 is a side view of the device of FIG. 5;

FIG. 8 is a schematic top view of a device for position control configured for angular motion according to an embodi ment of the invention;

FIG. 9 is a schematic cross-section view of the device of FIG. 8;

FIG. 10 is a schematic diagram of a bras Mess motor having three phases vised for position -control by individually controlling the phases according to an embodiment of the invention:

FIG. 1 i is a schematic i llustration of a prior art configuration of three phases;

FIG. 12 is a schematic illustration of a configuration of three phases for use with a device for position control according to an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a device and method for providing a functionality for position control using two independently controllable electromagnetic drive arrangements.

The principles and operation of a device and method according to the present invention may be better understood with reference to the drawings and the accompanying description.

The present invention is applicable to position control systems in which fast and accurate convergence over a small convergence distance is required. This is applicable to both linear and angular motion control systems. The linear motion embodiments described herein are of particular value when applied to processes, such as, for example, metrology, 3D printing, device inspection and the like, in which a head is moved in linear increments in order to systematically position the head in a. desired iocation to perform a function. The linear motion embodiments described herein are also of particular value when applied to semiconductor manufacturing processes. Such processes may include analysis processes in which a device, such as, for example, the wafer or fabricated semiconductor device, is moved in linear increments in order to systematically position the device such that points on the device can be inspected by an inspection device. These processes are commonly referred to as wafer metrology and wafer inspection processes. Semiconductor manufacturing processes also include fabrication processes, in which electronic circuits are created on a wafer by depositing layers of different materials on the wafer while incrementally moving a mask positioned above the wafer. The angular motion embodiments described herein are of particular value in applications that use high precision rotation stages, such as, for example, X-ray crystallography.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

Referring now to the drawings, FIG. 1 shows a schematic representation of a position control device 1. The schematic representation of the device 1 is intended to illustrate the general position control concept described in herein. Although the schematic representation depicts a device configured for linear motion, it is noted that a non- limiting exemplary embodiment of a device V configured for angular motion is presented in subsequent sections of the description herein. Furthermore, an exemplary non-limiting embodiment of the device 1 configured for linear motion is also presented in subsequent sections of the description herein.

The device J preferably includes a control unit 4, a primary motor 10, a secondary- motor 11. and a sensor arrangement 12. The control unit 4 preferably includes at least one processor 5 coupled to a storage medium 6 such as a memory or the like, Referring to FIG. 2, the control unit 4 is configured to actuate the primary motor 10 to provide a force profile to move an object 13 in an advancing direction towards a target position 3 along the path of movement of the object 13. When the device 1 is configured for linear motion, the path of movement of the object 13 is a substantially straight line. The control unit 4 is also configured to actuate the secondary motor Ϊ 1 to provide a resistive force opposing the movement of the object 13 as directed by the primary motor 10. In principal, the resistive force may be one of many components of force of the force profile provided fay the secondary motor 11 when actuated by the control unit 4. Other components of force may include, but are not. limited to, transverse forces and additional resistive forces, such as, for example, damping forces and the like. The resistive forces described herein are those components of force which are directionally opposing to the movement of the object 13 in the advancing direction, as will be described in more detail below. In certain operational scenarios, the resistive components of force may also be directionally opposing to the force provided by the primary motor 10. When the device 1 is configured for linear motion, the two above described forces act on the same line of motion in opposing directions. The control of the forces provided by the secondary motor 11 will be subsequently described.

The control unit 4 may include individual controllers for providing control functionality to the motors 10 and 11. It is preferable that the control functionality of the motors 10 and 11 is implemented using a single processing system with one or more processors in order to provide control functionality by a single device for controlling advancing movement by the primary motor 10 and forces resistive to that advancing movement by the secondary motor 11.

The processor 5 can be any number of computer processors, including, but not limited to a microprocessor, and ASIC, a DSP, a state machine* and a microcontroller. Such processors include, or may be in communication with computer readable media, which stores program code or instruction sets that, when executed by the processor, cause the processor to perform actions. Types of computer readable media include, but are not limited to, electronic, optical, magnetic, or other storage or transmission, devices capable of providing a processor with computer readable instructions.

The control of the primary motor functions to actuate the primary motor 10 to move the object 13 the entire distance in the advancing direction towards the target position 3, based on position information received by the sensor arrangement 12, as quickly and efficiently as possible using control techniques as known in the art. In a first mode of operation of the device 1, the movement toward the target position 3 is unimpeded by the resistive force or forces provided by the secondary motor 11, and is preferably aided by the secondary motor 11. The distance the object 13 moves in the first mode is referred to as the primary distance. As such, the motors 10 and 11 act to move the object 13 towards the target position 3 over the primary distance in unison, thereby exacting a total force from the motors 10 and II to move the object 13 in the advancing direction towards the target position 3.

The motors 10 and 11 are preferably implemented as linear motors. As is known in the art, linear motors operate along an array of magnets. Actuation of a linear^' motor by supplying a voltage induces a current which interacts with the magnetic field of the magnet array. Typically, linear motors, such as. for example, direct drive linear brushless motors, use coils of wire, most preferably copper wire, to facilitate the induced current. This interaction with the array of magnets provides the motors 10 and 1 1 the necessary force profiles for causing movement of the object 13, As will be discussed in more detail below, linear motors may be used in non-limiting exemplary embodiments of the device 1 configured for both linear and angular motion.

The sensor arrangement 12 is preferably mounted to the object 13 for sensing the position of the object 13, The sensor arrangement 12 may include transducers or the like or various other linear encoder or position sensor arrangements for sensing the position of the object 13. Once the object 13 has moved the primary distance in the advancing direction, the control unit 4 changes the mode of operation of the device 1 from the first mode to a second mode based on the sensor atxangement 12, in which the secondary motor 11 provides the at least one component of force resistive to tire advancing movement mentioned above. The distance moved in the advancing direction in the second mode of operation is referred to as the convergence distance. In typical applications using tire device 1, the primary distance is at least an order of magnitude greater than the convergence distance, in order to provide fast and accurate movement over the convergence distance, the at least one component of force varies as a direct function of the position of the object 13 relative to the target position 3. it is noted that the term ''direct function" is defined herein to be a function which is a function of a variable and not a function of the derivative or derivatives of that, variable. As such, direct functions of position do not include any functions which are functions of the velocity (first derivative of position with respect to time) or acceleration (second derivative of position with respect to time), in certain linear motion implementations of the device 1, such as, for example, wafer metrology and wafer inspection, the device 1 switches from the first mode to the second mode when the object 13 is within typically less than 10 μm, and in some cases within 1 -2 μm of the target position 3,

it is noted that the change in operation from the first mode to the second mode may alternatively be determined by the position of the object 13 as well as the velocity of the object 13. For example, the change in operation may occur slightly before the intended switching position if the object 13 is measured as moving at a velocity which is relatively less than the typical velocity of the object 13. Likewise, the change in operation may occur slightly after the intended switching position if the object 13 is measured as moving at a velocity which is relatively greater than the typical velocity of the object 13, Depending on the implementation of the device ί, the direct function of position may be a linear function, in which the dynamics of the at least one component of force behaves similar to the dynamics of the force on a linear spring, as will later he described. Alternative implementations may result in the direct function being a non-linear function ^•of position, in which the dynamics of the at least one component of feree behaves similar to the dynamics of the force of a non-linear spring. Since the at least one component of force is a function of position, the position of the object 13 may be converged quickly and accurately to the target position 3 over the convergence distance with the same or similar efficacy as with a physical spring system, with the advantage of the device 1 being that the object 13 may he subjected to a larger range of motion than that of an object connected to a physical spring.

As previously mentioned, the force profile provided by the secondary motor 11 may include additional resistive forces. An example of an additional resistive force is a component of force which varies as a function of the velocity of the object 13. When implementing the device I to include such an additional resistive force provided by the secondary motor 11, the dynamics of such a component of force behaves similar to the dynamics of the damping force of a damper, such as, for example, a viscous damper, as will later be described. As such, the overall dynamics of the force profile provided by the secondary motor 11 behave similarly to the dynamics of a mass-spring-damper system. It is noted that the resistive forces described above which are direct functions of position are preferably monotonie functions. The control of the resistive forces provided by the secondary motor 11 for the convergence over the final distance to the target position 3 is accomplished by use of feedback control. It is noted herein that such control functionality may be implemented as either a digital controller or analog controller. As is known in the art, digital control has several advantages over analog control, such as, for example, adaptability and flexibility. Although the controller may be implemented by either analog or digital control techniques, FIG. 3 depicts a non-limiting exemplary embodiment of an analog control circuit 20 as part of an overall analog feedback loop 2 in order to demonstrate the general position control concept described herein. It should be apparent to one of ordinary skill in the art that an analogous digital implementation of the control circuit 20 is possible using techniques known in the art. The processor 5 of the control unit 4 may be programmed to execute instructions representative of such an analogous digital implementation of the control circuit 20. As will be discussed, the feedback loop 2 includes components which model the overall system which is to be controlled. These components are herein described in order to better demonstrate the general position control concept.

Referring to FIG. 3, the feedback loop 2 includes an integrator block 27 for integrating twice, with time, a total force exacted on the object 13 to convert the force into a position signal, the control circuit 20 for executing control based on an input error signal, and a drive block 24 for converting the output of the control circuit 20 to a force to be differenced with, an external force to determine the total force exacted on the object 13. in the embodiments described herein, the integrator block 27 represents the system that is to be controlled, and as such, includes the object 13 to be moved and all associated components (the motors 10 and 11 , the sensor arrangement 12, the control circuit 20 and any hardware associated with the control circuit 20). in analogous terms, the output of the integrator block 27 can be described as the length of the spring of the previously mentioned analogous spring system. The external force is the force profile provided by the primary motor 10 to move the object 13 in the advancing direction. The force at the output of the drive block 24 is the resistive force or forces provided, by the secondary motor 11.

The block diagram of FIG. 3 is representative of a model of a control loop of an exemplary embodiment of the present invention and should not be taken to limit the invention to the exemplary implementation provided herein. The functionality of individual blocks may be combined with other blocks depending on the implementation and the intended application of the present invention.

The control circuit 20 includes electronic circuitry for executing control and preferably includes a first branch for multiplying the input to the control circuit 20 by a gain Kp 23, and a second branch for filtering the input to the control circuit 20 with a filter D(s) 21 and multiplying the filtered output by a gain K_D 22. The outputs of the branches are subsequently summed together and the summed output is used as input to the drive block 24.

It should be apparent to one of ordinary skill in the art that in the feedback, loop 2 depicted in FIG. 3, the control circuit 20 performs proportional control on the input position error signal and proportional control on the derivative of the input position error signal. In implementations in which the velocity of the object 13 is determined by a position sensor, the proportional control on the derivative of the input position error signal is accomplished by tfie filter D(s) 21. As is known in the art, the derivative of the eiTor signal may amplify higher frequency measurements or process noise that can cause large amounts of change in the output. As such, a low-pass filter is typically implemented in order to remove higher frequency noise components. Therefore, the filter D(s) 21 is preferably implemented as the cascade of a differentiator and a low-pass filter, the resulting transfer function in the s-domain given by:

where ω_v, is the pole location of the filter in radians per second. Equivalently, the pole location can be written as a frequency

(Hz), it is noted that in the feedback loop depicted in FIG. 3, the control circuit 20 is operative to convert the input position error signal into an output voltage. The output voltage is subsequently passed to the drive block 24 for converting the voltage into a force. It is noted that the drive block 24 includes a model of a current drive 25 which converts the input voltage into an electrical current. The model of the current drive may be represented as a first order low- pass filter G(s). The output of the current drive 25 is multiplied by a gain K_f 26, The gain K_F 26 is referred to as the raotor constant and is operative to convert the electrical current from the current drive 25 into a force. The cascaded output of the control circuit 20 and the current drive 25 effectively adjusts the induced current provided to the secondary motor 11. The output current from the current drive 25 when adjusted by the gain K_F 26 provides the resistive force or forces to the movement of the object 13 as directed by the primary motor 10. In the depiction of the feedback loop 2 in FIG. 3 , the current drive 25 has a transfer function in the s-domain given by:

where ω_(ί is the pole location of the current drive in radians per second. Equivalent!)_', the pole location can be written as a frequency

=

The location of the poles may be chosen using techniques and/or analyses known in the art such as, for example, root locus analysis. As such, in the feedback loop depicted in FIG. 3, it is preferred that Λ is between 300 Hz and 3 kHz,- and that k is between 500 Hz and 1.0 kHz.

The force component at the output of the drive block 24 corresponding to the first branch of the control circuit 20 corresponds to the component of force which varies as a direct function of the position of the object 13, namely the analogous spring force. Similarly, the force component at the output of the drive block 24 corresponding to the second branch of the control circuit 20 corresponds to the component of force which varies as a function of the velocity of the object 13. namely the. analogous damping force, The difference between a reference value and the output of the integrator block 27 is used to form the error signal which is used as input to the control circuit 20. In the feedback loop shown in FIG. 3, the reference value is given as the position of the object 13 when the device 1 switches from the first mode of operation to the second mode of operation. Since the output of the integrator block 27 is the length of the spring of the analogous spring system, the reference value can analogously be described as the free length of the spring of the analogous spring system. The error signal represents the position error between the target position 3 and the current position of the object 13, and by analogy, the compression length of the spring of the spring system. As previously mentioned, the integrator block 27 integrates twice, with time, the total force exacted on the object 13 to convert the force into a position signal. The integrator block 27 preferably includes a first integrator 28 for converting the force into a velocity, and a second integrator 29 for converting the velocity into a position. The control circuit 20 may further include a third branch for performing proportional control on the integral of the input position error signal. The output of the third branch may subsequently be summed with the outputs of the first and second branches as previously described, with the total summed output being used as input to drive block 24. it is noted, however, that since the desired convergence distance is relatively small, performing proportional control on the integrai of the input position error signal may have the imdessred effect of increasing the amount of time (i.e. the settling time) it takes for the position of the object 13 to converge to the target, position 3.

As previously mentioned, the sensor arrangement 12 may include transducers or the like or various other linear encoder or position sensor arrangements for sensing the position of the object 13 relative to the target 3. The sensor arrangement 12 may further include a velocity sensor for measuring the velocity of the object 13. in the depiction of the feedback loop 2 in FIG. 3, the position signal output from the integrator block 27 is used as input in order to generate both the analogous spring and damping forces output from the drive block 24. The proportional control on the derivative of the input position error signal is accomplished by the filter D(s) 21 in order to offset the effect of the second integrator 29. in implementations in which the sensor arrangement 12 further includes a velocity sensor, the output of the integrator 28 may be directly multiplied by the gain K_D 22 and summed with the output of the gain Kp 23, with the second branch of the control circuit 20 removed. Such an implementation has the advantage of reducing the complexity of the control circuit 20 and reducing the amount of measurement noise. However, it is noted herein that velocity sensors may be more difficult to mount to the object 13 than typical position sensors. Furthermore, typical, velocity sensors may be prohibitively more expensive than typical position sensors. As such, it may be more design efficient and cost effective to implement the control circuit 20 as shown in FIG. 3, in which the velocity of the object 13 is determined by differentiating (the filter D(s) 21} the position derived from a position sensor. It is noted herein that the sensor arrangement 12 may further include an acceleration sensor for measuring the acceleration of the object 13. Such an acceleration sensor may be used in place of or in addition to the previously mentioned velocity sensor, with correspondingly appropriate modifications made to the blocks of the feedback loop 2.

As previously mentioned, the position of the object 13 may be converged quickly and accurately to the target position 3 with the same or similar efficacy as with a physical spring or physical spring with a damper. Consider, for example, a physical mass-spring- damper system. Since the force provided to a mass attached to a spring and a damper is a combination of a direct function of the displacement of that mass (spring force) and a function of the velocity of that mass (damping force), moving the mass to a desired position can be accomplished by applying the appropriate amount of force to the mass in order to balance the force of the spring and the damping force, It is known that an ideal mass-spring-damper system having a mass m, spring constant k, and viscous damper of damping coefficient c can be modeled as a second order differential equation, The behavioral characteristics of such a system can be adjusted by tuning the undamped angular frequency,

which can be expressed as

and the damping ratio, which can be expressed as

/ Equivalency, the undamped angular frequency can be written as

(Hz), As such, appropriate selection of the parameters

results in the resistive forces provided by the secondary motor 1.1 behaving substantially as the mass-spring-damper system described above.

The parameters

may be selected as a function of the peak force provided by the secondary motor 1 J and the maximum convergence distance, A_max, when the device 1 is operating in the second mode as shown by:

In a non-limiting example, consider a peak force of 240 N provided by the secondary motor 11 with a. desired convergence distance of 10 μηι. This results in

As such, an angular frequency

_n of approximately 200 Hz results in a mass of 15 Kg being moved the desired distance ^ Since the variation of the at least one component of feree is generated by feedback control, the controller gains

can be adjusted by tuning the spring stiffness, dictated by spring constant

and the damping factor c. Specifically, the relationships between the spring system parameters and the controller gains are given by:

Likewise, the controller gains K_P and K_D can be tuned in order to adjust the spring stiffness and damping factor, so long as the value of each of the controller gains corresponds to the appropriate parameters (m, ζ and (On) being within the preferred ranges as mentioned above. Since the spring stiffness and damping factor dictate how quickly the position of the mass converges to a target position, appropriately adjusting the controller gains facilitates the corresponding adjustment of the rate of the convergence towards the target position 3.

Although it is preferred the position control device described thus far provides effective analogous spring and damping forces such that the position of the object 13 is converged to the target position 3 with the same or similar efficacy as with a physical spring damper, it is noted that the gains of the feedback, loop 2 may be appropriately adjusted in order to decrease the effective analogous damping force such that the position of the object 13 is converged to the target position 3 with the same or similar efficacy as with a physical spring.

FIG. 4 shows the results of a simulation, A plot of the settling time of the device 1 using the feedback loop 2 is shown along with a plot of the settling time of a prior art system overlaid to highlight the advantages of the present invention. The overshoot in the settling time of the device 1 can be attributed to a simulation artifact, and it is noted herein that the settling time of the prior art system plotted in FIG, 4 may also include such an overshoot. Referring again to the block diagram illustrated in FIG, 3, when the device 1 switches from the first mode of operation to the second mode of operation, input error signal is effectively zero, since the current position of the object 13 and the reference value are substantially equal. This implies that the analogous spring of the spring system is at the spring free length, or slightly offset from the spring free length if the mode switch is additionally based on the velocity of the object 13 as previously mentioned. This effective zero value of the input error signal causes the object 13 to move nearly unimpeded in the advancing direction. As the object 13 approaches target position 3₅ the input error signal increases, causing the output of the dri ve block 24 to increase (i.e. the resistive forces provided by the secondary motor ! .1 to increase). As such, the analogous spring of the spring system is compressed. Once the object 13 reaches the target position 3, the input error signal reaches its maximum value (i.e. the analogous spring is fully compressed), which causes the output of the drive block 24 to equalize with the external force, bringing the object 13 to rest. It should therefore be clear that at least one of the resistive forces provided by the secondary motor 11 varies as a direct function of the position of the object 13., with at feast one additional resistive force varying as a function of the velocity of the object 13.

Once the object 13 reaches the target position 3, the object may be moved to a new target position. As previously mentioned, this is of particular value when the device 1 is used in processes which require the systematic testing and evaluation of points of a device or devices, such as, for example, wafer metrology and wafer inspection. If the distance between consecutive target positions requires relatively large stroke length by the primary motor 10, for example distances larger than 10 μπι or in the millimetric range, the device 1 operates in the first mode until the object 13 is within the preferred convergence distance of the new target position. The device 1 subsequently switches to the second mode of operation as previously described, in situations where the distance between consecutive target positions is less than or approximately equal to the preferred convergence distance, the device 1 may operate exclusively in the second mode. The control unit 4 is preferably configured to receive a target position or a series of target positions in order to accommodate the sequential movement of the object 13. The designation of the primary motor 10 and the secondary motor 11 may be dynamic during operation of the device I . This may be particularly true when the same type of motor is used for the primary motor 10 and the secondary motor 1.1, and when thetwo motors 10 and I I operate at the same voltage. As such, the motors tasked with performing the functions of the primary motor 10 and the secondary motor 11 may change based on a variety of parameters, such as, for example, the direction of motion. In such an example, the motor tasked with performing the function of the secondary motor 11 is the motor closest in proximity to the current target position, in the schematic representation of the device 1 shown in FIG. 1, the direction of motion of the object 1.3 is shown by a solid arrow as moving to the right. As such, the secondary motor 11 is the right most motor, As previously mentioned, once the object 13 reaches a target position, the object may be subsequently moved to a new target position. Supposing, for example, that the new target position is to tire left of the object 13, the right most motor will assume the role of the primary motor .10 and the left most motor will assume the role of the secondary motor 11. As such, the feedback loop 2 provides control to whichever motor functions as the secondary motor 11 during the movement of the object 13 over the convergence distance.

In implementations in which different types of motors are used for the two motors, for example, one motor may operate at a higher voltage than the other motor, the designations of the primary motor 10 and the secondary motor 11 may not be dynamic. As such, the motor designated as the primary motor 10 may push or pull the object 13 towards the target position, depending on the location of the target position relative to the primary motor 10,

Referring now to FIGS. 5-7, an exemplary embodiment of the device 1 configured for providing linear movement of the object 13 is shown with the primary and secondary motors 10 and 11 and the sensor arrangement 12. The motors 10 and 11 are 'Shown in phantom in FIG. 6. In a particularly preferred but non-limiting implementation, each of the motors 10 and 11 are linear motors, such as, for example, ETEL Iron Core motors. As previously mentioned, linear motors operate along an array of magnets 14 and the actuation of linear motors induces a current which interacts with the magnetic field of the magnet array. The sensor arrangement 12 is implemented as a linear encoder assembly, such as, for example, Heidenhain LIP 281 , for sensing position. The linear encoder assembly includes a reading head 12b which moves along a scale 12a for encoding position. The electronic components of reading head 12b are preferably encased in a housing or the like. As shown in FIGS, 5-7, the reading head 12b is connected to the object 13 via an arrangement of hardware fasteners such as, for example, bolts, screws, and the like. The motors 10 and 11 are configured to move along a suitably shaped profile provided by guide rails, tracks or the like, which enable movement in the designated X linear direction. In the exemplary embodiment shown in FIGS. 5-7, the suitably shaped profile is provided by guide rails 15a and 15b. The guide rails 15a and 15b are preferably direct drive types known in the art which use ball bearings and the like for enabling movement along the rails.

As shown in FIGS. 5-7, an ^'arrangement of slides is positioned adjacent to each of the motors 10 and 11 for enabling movement along the guide rails 15a and 15b. Specifically, a first slide 16a and a second slide 16b are positioned on opposing sides of motor 10. and a third slide 16c and a fourth slide 1.6d are positioned on opposing sides of motor 11. The slides 16a and 1.6c are configured to move along the guide rail 1.5a, and the slides 16b and 16d are configured to move along the guide rail 15b, The object 1.3 is connected to the slides 16a-16d via an arrangement of hardware fasteners 30 such as, for example, holts, screws, and the like. The object 13 is additionally connected to each of the motors 10 and 11 via an arrangement of connectors 31 such as, for example, pins and the like, in the exemplary embodiment depicted in FIGS. 5-7, each of the motors 10 and 11 is connected to the object 13 via two connectors 31.

Device 1 preferably includes oppositely disposed stoppers 18a and 18b. As shown in FIGS. 5-7, the stopper 18a is preferably disposed at a first end of the guide rails 15a and 15b, and the stopper 18b is preferably disposed at a second end of the guide rails 15a and 15b. The stoppers 18a and 18b are preferably interposed between the guide rails 1.5a and 15b. The magnets 14 are arranged along the length of the guide rails 15a and 15b such that there is appropriate coverage over the working range of motion of the object 13. The magnets 14 may be arranged in groups, each group being placed on a removable plate. The plates may then be positioned along the length of the guide rails 15a and 15b. This implementation allows for groups of magnets to he more easily removed for inspection or replacement. The interconnected arrangement of the motors 10 and 11 , the slides 16a-16d, and the object 13, in combination with the magnets 14, enables the object 13 to move over the range of motion.

it is noted that using two guide rails and two slides per motor provides more stable movement along the X-axis, and reduces movement and oscillation in the Y direction when moving substantially along the X-axis, However, alternative implementations are possible in. which a single guide rail is provided for facilitating the movement of each motor.

A cable chain 17 is connected to the device 1 for facilitating the connection and supply of peripheral components and materials to the components of the device I. For example, power is supplied to the sensor arrangement 12 and the motors 10 and 11 via an arrangement of power cables and/or connectors through the cable chain 17. The cable chain 17 may additionally facilitate the supply of materials and/or control signals to a head or other distributing components of the device 1. in the non-limiting example of 3D printing, the head would be implemented as a printing head. Tubing for supplying the head with 3D ink, and electrical connectors for providing the head with control signals, would be delivered to the head via the cable chain 1.7.

In the non- limiting example of device inspection, the head could be implemented as part or all of an imaging system for performing inspection on points of a device. Connectors for providing electrical communication between the imaging system head and the imaging system would be delivered via the cable chain 17.

It should be apparent that in the non-limiting examples previously mentioned, the actuation of the head to perform the desired function is controlled by a controller and is preferably coordinated with the movement of the head. The controllers of the head and the motors 1Θ and 11 may be implemented using a single processing system with one or more processors in order to provide control functionality by a single device for controlling movement of device 1 and actuation of the head. Furthermore, the heads of the above mentioned examples may be attached to or encased in the housing of the reading head 12b. In the non-limiting embodiment, described with reference to FIGS. 5-7, the motors 10 and 11 of the device 1 travel with the object 13 as the object moves towards the target position. It is noted, however, that alternative implementations of such an embodiment are possible in which one or both of the motors 10 and II are stationary components which remain in a fixed position as the object 13 moves towards the target position.

As previously mentioned, the position control concept is of particular value in applications in which an XY table is employed to move in two independent directions, namely an X-axis direction and a Y-axis direction. It is noted herein that such movement along the X-axis and Y-axis is substantially linear, and therefore the position control concept described above may be applied to each individual axis. As such, a first device may be employed for providing position control along the X-axis and a second device may be employed for providing position control along the Y-axis. In such an implementation, each position control device would preferably include two motors controlled by a controller. The controllers for the X-axis and Y-axis may be implemented using a single processing system with one or more processors in order to provide control functionality by a: single device for controlling position in both the X-axis and Y-axis directions.

As previously mentioned, the present invention is also of particular value in angular motion systems, specifically those that employ high precision rotation stages. As such, an embodiment of device 1 ' for providing such rotational movement is shown in FIGS. 8 and 9, It is noted that the functionality of such a device for providing angular movement is generally similar to the functionality of the device for providing linear movement unless expressly stated otherwise, and will be understood by analogy thereto. For simplicity, the sensor arrangement for sensing position is not shown in FIGS. 8 and 9.

The specific differences between the linear movement embodiment and the angular movement embodiment are several of the quantities used for describing the movement of the object 13. For example, in the angular movement embodiment, the forces provided by the motors 10 and 11 result in rotational forces for rotating the object 13 about a central axis. As such, the linear forces provided by the motors in the linear movement embodiment are replaced analogously by torque, which is a function of the provided rotational forces. Furthermore, the mass of the object being moved in the linear movement embodiment is replaced analogously by inertia. Finally, the spring stiffness, dictated by spring constant A% in the linear movement embodiment is replaced analogously by angular stiffness. The operation of the angular movement embodiment will now be described,

The primary motor 10 rotates the object 13 towards a target position along the path of rotation of the object 13. The rotation of the object 13 is about a central axis of rotation 19. In the first mode of operation, the rotation towards the target position is unimpeded by the secondary motor 11, and is preferably aided by the secondary motor 11. As such, the motors 1(1 and 11 act to rotate the object 13 towards the target position in unison. In the second mode of operation, the secondary motor 11 provides a resistive rotational force to the rotational force provided by the primary motor 10. For example, the primary motor 10 may rotate object in the clockwise direction, whereas secondary motor provides a counter clockwise rotational force resistive to the primary motor 10 rotation. As in the linear movement embodiment, at least one of the resistive forces provided by the secondary motor 11 varies as a direct function of the rotational position of the object 13 relative to the target position, with at least one additional resistive force varying as a function of the angular velocity of the object 13.

Similar to the embodiment depicted in FIGS. 5-7, the path of angular movement may be defined by a suitably shaped profile provided by bearings, tracks or the like. The bearings are preferably fastened to a stationary mounting or the like, such that the object 13 rotates about the axis of rotation 19 when the motors 10 and 11 move along the bearings. For example, a bearing may have a substantially circular profile, such that when each motor is connected to a slide for moving along the bearing, the resulting path of motion is substantially circular. As depicted in FIG. 8, an array of the magnets 14 is deployed in a substantially circular arrangement corresponding to the desired path of angular movement of the object 13. For simplicity, the object 13, to which the motors 10 and 11 are connected, is not shown in FIG. 8, but is shown in FIG. 9.

Although the device described thus far has pertained to position control using two motors having components of force which are substantially opposing to one another with one of the components of force varying as a function of the position of the device relative to a target position, other embodiments are possible in which the same or similar resulting affect is achieved by using a single motor, A non-limiting example of a device 100 according such an embodiment is described below with reference to FIGS, 10-12.

As previously mentioned, linear motors such as, for example., direct drive linear brushless motors provide motion via an interaction between an induced current and the magnetic field from an array of magnets. Linear brushless motors typically include a stator consisting of a plurality of North- South pairs of pemianent magnets 102, and a rotor which consists of a plurality of electromagnets, where each electromagnet, is operated by a separate coil of wire, also referred to as a phase 104. The individual pairs of the permanent magnets 102 are denoted as 102-1 , 102-2, etc. The North-South magnets of each individual pair of the pairs of permanent magnets 102 are denoted as 102-1B and 102-1 A (for the first pair 102-1), 102-2B and 102-2 A (for the second pair 102-2), etc. Most typically, the rotor of a brushless motor consists of three electromagnets, and therefore, is operated by three phases, denoted by a first phase 104 A, a second phase 1.04B, and a third phase 104C. in direct drive linear brushless motors, the pairs of pemianent magnets 102 are positioned in an array, similar to that of the magnet array 14 of FIGS. 5 and 6. As such, the device for position control as previously described may he implemented by using a single motor and controlling the individual phases 104A-1O4C of that motor.

Referring now to FIG. 10, the length of the pair 102-1 of North-South permanent magnets is referred to herein as the magnetic period. The motor coils (or phases) 104A- 104C are arranged such that the distance (in the magnetic sequence) from each electromagnet of the rotor to a neighboring electromagnet is equal to one third of the magnetic period, in the example shown in FIG. 10, the phase 104A is substantially aligned with the South pemianent magnet 1.02-1 A, the phase Ϊ04Β is one third of the magnetic period forward of the phase 104A such that it is substantially aligned with one third of the South magnet 102-2 A and two thirds of the North magnet. 1Θ2-2Β of the second pair of magnets 102-2. The phase 104C is one third of the magnetic period forward of the phase 104B, and for completeness, the phase 104A is one third of the magnetic period behind the phase 104C As such, the phase 104C is substantially aligned with one third. of the South magnet 102-4 A and two thirds of the North magnet 102-4B of the fourth pair of magnets 102-4.

Before explaining the position control by use of a single motor with the three phases 104A-104C, it is important to note that in typical three phase brushless motors, one terminal of each of the three phases is connected together resulting in what is known in the art as a "star'^* or "wye" winding (FIG. 11 ), In such a configuration, the currents in the phases .104A-104B are determined by setting appropriate voltage levels to the unconnected terminals of each phase. The position control concept by use of a single motor with the three phases 104A-I04C can be accomplished by changing the phase connection from the "star" configuration of FIG. 1 1 to a separate phase configuration, as shown in FIG. 12.

Referring now to FIG. 12, the six terminals of the phases 104A-104C are connected to a motor drive. The motion of object over the primary distance is facilitated by distributing the input current between the phases 104A-104C according to the position of each individual phase with respect to the magnetic period. This may be achieved by shortcutting one terminal of each phase inside the motor drive and setting the voltage on the other terminal in the same way as in a "star" connection (FIG. 1 1), or by setting the correct voltage difference between each of the phase terminals separately.

The object is moved over the convergence distance by controlling individual phases, it is noted that preceding the control of the phases of the device 100, a selection is made for which of the phases functions as the primary motor 10 and which of the phases functions as the secondary motor 11, Such a selection is based on a logical mapping of phase to position. Such a mapping may be accomplished by determining the coil positions using a Hall effect sensor. As such, the sensor arrangement 12 may further include at least one Hall effect sensor. The two phases which are closest to the crossing point between the pairs of permanent magnets 102 function analogously as the primary motor 10 and the secondary motor I I. The current to each phase is controlled by a controller functionally equivalent to the control unit 4. As such, one of the two phases functions as the secondary motor 11. and the current supplied to that phase is contiOlied by a control loop functionally equivalent to feedback loop 2. Since the two phases function as the primary motor 10 and the secondary motor

11, the motor constant for each of the two phases will be different. The motor constants of those phases are each a function of the position of the phases relative to the magnetic period. Specifically, the value of the motor constant of a specific phase i is given by:

where k_i is the motor phase constant of phase i, x is the position of the rotor from a reference point, p is the magnetic period, and km is the motor constant when the phase is substantially aligned with the crossing point between the pairs of permanent magnets 102, as depicted by the phase 104 A in FIG. 10. The position x may be measured, for example, by the sensor arrangement 12, The variable

is the distance of phase i from an equilibrium point when the position x is substantially zero. The equilibrium point is defined as the point where phase i is substantially aligned with the North magnet of one of the pairs of permanent magnet 1.02. As such,

is the difference between the position of phase i when x is substantially zero and the position of phase i when positioned close to the equilibrium point. It is noted that the variable

can take on both positive and negative values. As previously mentioned with reference to the implementations of FIGS. 1-9, the controller gains K_F 23 and K_D 22 can be adjusted by tuning the motor constant, of the phase which functions as the secondary motor 11.

It is noted that the position control implementation using a single motor with individually controllable phases is of particular value when the convergence distance is small in comparison to the magnetic period. For example, in semiconductor manufacturing processes in which an XY table is used, the convergence distance is 5 nm - 10 μηι. By contrast, the magnetic period is typically on the order of a few tens of millimeters, which is three orders of magnitude larger than the convergence distance, It will be appreciated thai the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS;

1. A device for position control comprising:

(a) first and second electromagnetic drive arrangements in mechanical driving relationship with an object, said electromagnetic drive arrangements being independently controllable;

(b) a sensor arrangement functionally associated with said object for .determining position of said object; and

(c) a control unit associated with said sensor arrangement and said first and second electromagnetic drive arrangements, said control unit configured to actuate said first electromagnetic drive arrangement to provide a force profile to move said object in an advancing direction towards a target position, said control unit further configured to actuate said second electromagnetic drive arrangement to provide a force profile including at least one component of force resistive to movement of said object in said advancing direction by said first electromagnetic drive arrangement, said at least one component of force varying as a direct function of position relative to said target position over a range of positions- including said target position.

2, The device of claim 1 , wherein said function of position is a linear function ,

3, The device of claim 1 , wherein said function of position is a non-linear function.

4. The device of claim 1 , wherein said force profile provided by said second electromagnetic drive arrangement further includes at least one component of force varying as a function of the velocity of said object.

5. The device of claim 1, wherein the movement in said advancing direction is linear movement.

6. The device of claim I , wherein said at least one component of force and the force profile provided by said first electromagnetic drive aiTangement are substantially opposing forces.

7. The device of claim 1 , wherein the movement in said advancing direction is angular movement.

8. The dev ice of claim 1, wherein said object includes a movable table,

9. The device of claim 1 , wherein said function of position is a monotonic function of position.

10. The device of claim 1 , wherein said first and second electromagnetic drive arrangements are motors,

1 1. The device of claim 10, wherein said first and second motors are linear motors.

12. The device of claim 1 , wherein said first and second electromagnetic drive arrangements are separate windings of a single motor.

33. The device of claim 12, wherein said motor is a linear motor.

14. The device of claim 12, further comprising:

(a) an aiTangement of permanent magnets for providing the mechanical driving relationship of said windings with said object; and

(b) a sensor configured for determining position of said associated electromagnets relati ve to said arrangement of permanent magnets, wherein each said winding is associated with an electromagnet.

15. The device of claim 1 , wherein said control unit includes a feedback loop for providing a control signal to control said at least one component of force.

16. The device of claim 15, wherein said feedback loop includes a controller with at least one adjustable gain.

17. The device of claim 16, wherein said controller includes at least one component for providing derivative control of an input signal

18. The device of claim 1.6, wherein said controller includes at least one component for providing proportional control of an input signal.

1.9. The device of claim 1 5, wherein said feedback loop includes a first-order low pass filter.

20. The device of claim I , wherein said control unit is further configured to actuate said second, electromagnetic drive aiTangement to provide a force profile to move said object in said advancing direction, and wherein said device is operable in a first mode, in which said force profile provided by said second electromagnetic drive aiTangement moves said object in said advancing direction, and a second mode, in which said force profile provided by said second electromagnetic drive aiTangement is resistive to movement of said object in said advancing direction by said first electromagnetic drive aiTangement.

21. The device of claim 20, wherein a change in operation from said first mode to said second mode is based on the position of said object.

22. The device of claim 20, wherein a change in operation from said first mode to said second mode is based on the velocity of said object,

23. The device of claim 1, wherein said sensor arrangement includes a position sensor.

24. The device of claim 1, wherein said sensor arrangement includes an acceleration sensor.

25. The device of claim 1, wherein said sensor arrangement includes a velocity sensor.

26. The device of claim 1 , wherein said control unit is further configured to receive a target position as an input, and wherein said control unit is further configured to actuate said first electromagnetic drive arrangement to provide said force profile to move said object towards said input target position.

27. The device of claim 1 , wherein at least one of said first and second electromagnetic drive arrangements travels with said object as said object moves towards said target position,

28. The device of claim 1, wherein at least one of said first and second electromagnetic drive arrangements remains in a fixed position as said object moves towards said target position,

29. The device of claim 1, wherein said control unit comprises at least one processor and a data storage medium.

30. A method of position control comprising:

(a) actuating a first electromagnetic drive arrangement using a controller to apply a force on an object to move said object in an advancing direction towards a target position; (b) detecting a parameter of said object through a parameter sensor for providing a signal to control a second electromagnetic drive arrangement; and

(c) controlling said second electromagnetic drive arrangement according to said signal to provide a force profile including at least one component of force resistive to movement in said advancing direction.

31. The method of claim 30, wherein said control of said second electromagnetic drive arrangement is provided by a feedback loop having at least one adjustable gain, the method further comprising:

(a) controlling a rate of convergence of the object towards said target position by adjusting said at least one gain.

32. The method of claim 30, further comprising:

(a) actuating said second electromagnetic drive arrangement to apply a force on said object to move said object in said advancing direction towards said target position.