Motor thermal management by field-oriented control currents

Abstract

Apparatus and methods are provided for stabilizing a temperature of a motor of a metrology system, wherein field-oriented control (FOC) components of input currents of the motor are a direct (!< / ) current component aligned with the magnetic field of the moving primary, causing no motor motion, and a quadrature (I9) current component perpendicular to the magnetic field of the moving primaries, generating motor motion, and wherein an Id current component is applied to the motor causing the motor temperature to reach and / or to maintain a value within a previously determined temperature range.

Description

MOTOR THERMAL MANAGEMENTBY FIELD-ORIENTED CONTROL CURRENTSFIELD OF THE INVENTION

[0001] The present invention relates generally to the field of linear motor positioning, and in particular to techniques for improving positioning accuracy.BACKGROUND

[0002] Metrology and inspection measurements are critical for ensuring the accuracy and reliability of certain manufacturing processes, for example, in semiconductor inspection processes, such as optical defect detection. These measurements often rely on the precise positioning of a stage supporting an object under inspection. Other computer numerical control (CNC) processes, such as high precision machining also depend on positioning repeatability. However, position accuracy is contingent on several factors, including the thermal stability of the motors used for positioning. Thermal variations can cause variations in motor motion, resulting in positioning errors. Such errors result either in lower accuracy or in process inefficiencies, as positioning errors must be corrected by feedback mechanisms processed in real time.

[0003] However, efforts to manage the motor temperature to reduce positioning errors are complex, and generally require additional heating elements and sensors, which in turn also require additional calibration processes.

[0004] Temperature variability is primarily due to the variability of currents supplied to the motor. Different positioning applications impose different motor workloads, causing heat variations in the motor from job to job. Note that brushless motor currents are oftendefined by direct and quadrature currents, as described in US Patent 7,023,168 Bl, to Patel, et all., titled, “Field weakening motor control,” incorporated herein by reference.

[0005] Linear, ironless, brushless motor configurations widely used in metrology equipment, whether moving magnet or moving coil types, often employ multi-axis configurations such as XY, XYZ, or XYZ-R (rotation) stages, and therefore face compounded challenges due to the interaction between the thermal behavior of each motor. As each axis introduces an additional degree of freedom (DOF), there is a cumulative effect on accuracy.

[0006] Methods for minimizing thermal effects on positioning accuracy often rely on preliminary motor axis heating or on predictive models of positioning errors. Such methods for controlling and / or compensating for thermal variations are described in patents such as: US Patent 6,167,634, to Pahk, et al., “Measurement and compensation system for thermal errors in machine tools”; US Patent 6,471,451, to Kojima, et al., “Method of correcting thermal displacement of machine tool”; and US Patent 7,266,903, to Sato, “Method for correcting thermal displacement in a machine tool,” all of which are incorporated herein by reference.

[0007] An additional publication that covers the subject is: “Error compensation in machine tools — a review: Part II: thermal errors,” by R Ramesh, M. A Mannan, and A.N Poo, in International Journal of Machine Tools and Manufacture, Vol. 40, Issue 9, July 2000, Pages 1257-1284.

[0008] Two related online publications include: “ThermoComp® Integrated Temperature Compensation,” by Aerotech, at www.aerotech.com, and “Controlling Thermal Expansion,” by David Goosen, of Zaber, published at www.zaber.com.

[0009] Despite improvements made by these methods, the management of motor thermal effects remains a complex process, prone to error and inefficiency. For example, preliminary heating during an idle state requires additional hardware and can cause varying temperature gradients that differ from those generated during motor operation. Predictive modelling requires extensive experimentation for model calibration and adaptation, as well as additional sensor hardware.

[0010] Improved thermal management would result in more stable axis mechanics, leading to superior positioning accuracy and repeatability for metrology and other industrial processes, such as CNC machining. It is within this context that the embodiments of the present invention arise.SUMMARY

[0011] Embodiments of the present invention provide apparatus and methods for stabilizing motor temperatures to improve motor positioning accuracy over varying operating conditions and load cycles. Accurate positioning and measurement of semiconductor wafers are critical to meet strict specifications of many manufacturing processes, in particular processes in the semiconductor industry. Thermal fluctuations in a motor affect the precision of control over positioning apparatus.

[0012] Positioning motors are generally controlled through field-oriented control (FOC), by which motor current is specified by two perpendicular components, a direct (D) current and a quadrature (Iq) current. The Iqcurrent component, perpendicular to the magnetic field of the motor’s primary, is applied to the motor to cause motion, such as motion for positioning a measurement stage, whereas the D current component, aligned with the magnetic field, can affect magnetic flux but causes no motor motion. Inembodiments of the present invention, the Idcurrent component is applied to heat the motor, in conjunction with any heating caused by the Iqcurrent component. The application of the Id current component to stabilize the motor temperature results in improved positioning accuracy for a wide range of industrial applications.BRIEF DESCRIPTION OF DRAWINGS

[0013] For a better understanding of various embodiments of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings. Structural details of the invention are shown to provide a fundamental understanding of the invention, the description, taken with the drawings, making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

[0014] In the accompanying drawings:

[0015] Fig. 1 is a schematic diagram of a positioning system 100 configured to stabilize motor temperature by applying an FOC Idcurrent component, according to some embodiments of the present invention;

[0016] Fig. 2 presents graphs illustrating the behavior of FOC currents during execution of a motor routine, according to some embodiments of the present invention;

[0017] Fig. 3 depicts graphs of motor temperature variations with and without the closed RMS current control loop, according to some embodiments of the present invention; and

[0018] Fig. 4 is a flow chart of steps implemented by a positioning system 100 configured to stabilize motor temperature by applying an FOC Idcurrent component,according to some embodiments of the present inventionDETAILED DESCRIPTION

[0019] It is to be understood that the invention and its application are not limited to the system and methods described below or to the arrangement of the components set forth or illustrated in the drawings, but are applicable to embodiments that may be practiced or carried out in various ways.

[0020] Brushless motors, such as permanent magnet, synchronous rotary motors (PMSRMs) and permanent-magnet, synchronous linear motors (PMSLMs), are widely utilized in precision motor applications. These motors are generally controlled through field-oriented control (FOC), which separates the motor current into two components, a direct (L) current and a quadrature (Iq) current, where the Idcurrent component is aligned with the magnetic field of the motor’s moving primary, causing no motor motion, and the Iqcurrent component is perpendicular to the magnetic field (and to the Idcurrent component), generating motor motion. Typically, Iqis controlled according to the force required to cause motor motion, while Idis often set to zero or adjusted to achieve specific flux conditions such as field weakening.

[0021] In particular, for a non-salient, ironless motor primary, whether the primary is a moving permanent magnet or moving coil, the inductance path is the same for both Iqand L current components, the reluctance component of the electromagnetic force is close to zero and the axis (i.e., moving primary) force is provided by Iq, not L, current components.

[0022] A motor’s temperature increment over ambient temperature, AT, for a three- phase current motor drive can be expressed in terms of the RMS motor current supplied from the motor drive (i.e., power amplifier) as:where,IRMS is RMS current (Amps);RL-L is line-to-line terminal resistance of each phase of current (Ohms);Rth is thermal resistance (°C / W); represents total motor power loss (W), whichrepresents the heating power supplied to the motor by the Iqand Idcurrent components.

[0023] For a brushless motor, IRMS of the phase currents is equivalent to IRMs of the Iqand Idcurrent components, that is:where Iqand Idare expressed as peak currents.

[0024] Reference will now be made to the figures, which elucidate embodiments of the present invention.

[0025] Fig. 1 illustrates a schematic diagram of a system 100 configured to provide IRMS current to a motor’s windings to generate both motion and to set and maintain a stable temperature for improved positioning accuracy during motor operation.

[0026] System 100 typically includes several standard components: a motor 110 thatcan be controlled by FOC, also referred to as vector control, and a motor drive 120 that performs the FOC calculations and generates drive currents 130 for the motor. As indicated, the motor typically has coils 112, which receive the drive currents, and a motor axis 114, or carriage, which moves or rotates, i.e., is “positioned,” according to the electromagnetic force generated in the coils. It should be noted that heat generated by the flow of current in the motor coils 112 is dissipated to other motor components, primarily the motor axis / carriage 114, primarily by conduction.

[0027] The motor drive 120 typically receives a motion signal from a motion controller 122, which is typically programmed to perform a motion (i.e., “positioning”) routine, typically by generating Iqsignals calibrated to correspond to the desired motions. An FOC module 124 receives Iqreference signals 126 (which generate motor motion) and Idreference signals 128 (which may affect magnet flux, as described above). The FOC module applies transforms of the Idand Iqto generate signals corresponding to the drive currents 140 that are applied to the motor coils. In particular, the FOC module 124 may apply an inverse Park transform, which converts the IdandIqreference signals (“FOC current components”) to three-phase drive current signals 130, which then may be amplified by an amplifier 132. The amplifier may, for example, employ pulse-width modulation (PWM) to drive a three-phase inverter that supplies the drive currents 140 (i.e., coil currents a, b, and c).

[0028] Typically, the system also includes feedback to maintain stability of the motor operation. For example, the voltages and / or currents of the motor phases may be measured and provided as motor feedback 142 to the FOC module 124, which may then apply a transform, such as the Park transform, to convert the motor feedback 142 to Idand Iqfeedback 144. As indicated, this Idand Iqfeedback may be provided to the motion controller122, which may adjust the input Iqsignal accordingly to achieve the desired motion control. (The feedback can also be applied to implement RMS motor and / or amplifier protection.)

[0029] In typical motor control systems, different motor positioning routines often require different levels of power, that is, different intensities of the Iqcurrent component. Consequently, the heat generated by different positioning routines varies, not only during a positioning routine but also from one routine to the next. In order to maintain a stable motor and axis carriage temperature across different routines, a temperature target for the motor may be selected that is above the level of temperature that would be reached by any typical positioning routine. An additional heating power, that is, in addition to the Iqcurrent component, may then be applied, such that the combined power of the Iqcurrent component and the additional heating power can maintain the increment of temperature above ambient power according to equation (1), above. In embodiments of the present invention, the Idreference signal is applied to the FOC module to generate this additional heating power component, which heats the motor rather than generating motion.

[0030] With proper calibration of the effect of total power input of the Idand Iqcurrents on temperature, or, equivalently, the effect of their combined RMS input current, the motor temperature can be stabilized within a narrow range by maintaining a target heating power input (or equivalently, a target RMS current). In addition, the motion generated by the Iqcurrent component may be calibrated at the given temperature (i.e., within the given range), to provide a calibrated level of positioning accuracy.

[0031] Heating by an Idcurrent component may be applied both when a motor is idle, i.e., no Iqcurrent component is applied, and during execution of a motor positioning routine, which typically involves intermittent application of the Iqcurrent component.

[0032] As indicated in Fig. 1, the Idreference signal applied to complement the Iqcurrent component may be provided by an Idreference controller 150. In a simplistic configuration, the Idreference controller may be programmed to simply complement a pattern ofIqconfigured by a pre-set positioning routine. That is, the Idreference may be varied to balance theIqto provide a total power level equal to the heating power required to maintain the target temperature. In a more precise configuration, the Idreference signal may be generated by the Idreference controller 150 in real time, according to the feedback 144 from the motor drive 120.

[0033] For example, a calculator routine 160 may be configured to apply the above equations, to calculate, from the Idand Iqfeedback 144, the heating power supplied by the Iqand Idcurrent components, or an equivalent indicator, such as total RMS current. The feedback 144 is typically a signal measured with a high sampling rate of, for example 100 samples / sec, to prevent spikes in the control loop steps. The output of calculator 160 may therefore be considered a signal representing an “instantaneous” heating power value.

[0034] The instantaneous heating power may be further modified by a thermal model 162, configured as a first order low pass filter with transfer function HLPF(s), for example, as a simplified motor thermal flow model, such as:where,Tis a motor thermal time constant (in seconds), and s is Laplace operator.

[0035] The transfer function HLPF(s) may be configured to convert the instantaneousheating power feedback signal 144, or, alternatively, RMS current, to a smoothed signal representing the heat loss from the motor, according to the motor thermal time constant.

[0036] The summator produces an error (i.e., a correction), which may be a power input error calculated as an algebraic sum of the target heating power required to maintain the target temperature and the estimated heating power feedback. As described above, the target may alternatively be target RMS current, as the current squared is proportional to the power, in which case the feedback summator 164 can produce an RMS current error according to equation (3).

[0037] As indicated, a preset target 166 (heating power, RMS current, or temperature) may be provided to a profiler 168, which may be configured to provide a conditioned value to the summator. For example, the profiler may be configured to provide an initial “heating period,” whereby the target value input to the summator ramps up over a period of time from a preset ambient temperature to the preset target 166, preventing the summator from outputting an extreme correction value.

[0038] The correction value from the summator is input to a control filter 170, which may be a proportional filter or, for greater precision, a Proportional-Integral-Differential (PID) filter or similar filter to smooth the resulting Idreference signal. The control filter 170 may also include a “limiter” to limit Idreference signal to a maximum level (which may be based on the motor or power amplifier ratings). Typically, the Idreference 126 is restricted to negative values to prevent magnetic flux saturation. It may be noted that a PID filter would typically smooth fast gradients of correction, simulating the rate of real thermal processes, such that the functions of the profiler 168 and of the thermal model 160 would not be needed to preprocess the signal applied to the summator.

[0039] Fig. 2 presents plots 200 illustrating the behavior of Id, Iq, and total Irmscurrents when an operating routine is executed. The indicated operating routine shows a scenario in which the Iqcurrent 201 shows the same pattern repeated multiple times with intervening idle periods, which is the type of routine typical for a repetitive metrology process. Upon execution Id, current 202 varies accordingly to achieve a target heating power (or total RMS current value). With the filtering as described above, the resulting RMS current level 203 shows some minimal ripple (e.g., <0.1 A), ensuring a stable temperature of the motor and axis carriage. Note that Idis negative, such that during an idle state ( Iq201 close to zero), U 202 is low, meaning that the absolute value of Id202 is high. When motion commences ( Iqis applied to generate the necessary force for the motion profile), the absolute U component decreases according to equation (2). Idmay be chosen to be negative to avoid magnetic flux saturation.

[0040] Fig. 3 depicts graphs 300 showing motor temperature variations with and without the application of Idacross different operating routines (after initial heating to reach the target heating power, RMS current, or temperature. Graph 301 shows temperature fluctuations with Idapplied to stabilize the temperature during operation (after an initial heating process, not shown). Graph 301 shows that the total heating power is calibrated together with a target ambient temperature and thermal resistance so that the temperature remains within a small range (indicated as 0.25°C).

[0041] Graph 302 illustrates the variation in temperature during operation without U compensation (the graph indicated the temperature after a period of initial operation that raises the motor temperature above the ambient temperature). The application of varying Iqover time causes a temperature variation of 3°C. Graph 303 shows a characteristic value of ambient temperature, which varies slightly with air conditioning operation.

[0042] Fig. 4 is a flow chart 400 of steps implemented to prepare the positioning system 100 and during operation of the positioning system to stabilize motor temperature by applying an FOC Idcurrent component, according to some embodiments of the present invention. An initial step 402 may include determining a reference motor temperature, that is a target temperature appropriate for a given combined heating power of an Iqcurrent component and a compensating Idcurrent component.

[0043] At a subsequent step 404, Iqcurrent component, the speed and position control with respect to the Iqcurrent component may be calibrated at the reference temperature, thereby leveraging the repeatability achieved by a constant temperature to improve not just relative accuracy but absolute accuracy.

[0044] At a step 406, the target may be set for the control system. The target may be, for example, an average heating power and / or RMS current needed to maintain a reference (i.e., target) temperature.

[0045] At a step 408, during an idle state before an operational positioning routine (which may be, for example, for metrology or manufacturing), an initial heating period may be applied, using an Idcurrent component, to reach the target temperature.

[0046] At a step 410, once the target temperature is reached, the system starts execution of a positioning routine, with initial phase currents applied according to the transform (i.e., inverse Park transform) of an initial Iqcurrent component.

[0047] With the start of the routine, a feedback step 412 is also performed, with the measured motor parameters (e.g., coil currents) transformed to Iqand Idvalues that are provided as feedback to the Iqand Idcontrol loops.

[0048] At a step 414, the Idcontrol loop (Irf reference controller 150 of Fig. 1) generatesan Idreference for the motor drive, to compensate for the measured Iq, in order to achieve the target heating power for maintaining a constant motor temperature. Note that both f. and Idvalues are typically provided as feedback to the Iqcontrol loop as well, as the Iqcontrol loop may take Ideffects on flux into account when calculating Iq.

[0049] The new Idreference, together with the newIqreference, are received by the motor drive to generate new motor currents. Process 400 continues in a loop from step 420 to step 412 until the given operating routine is done (at step 430).

[0050] EXAMPLES

[0051] A first example of the invention described herein (“example 1”) is a control unit for a stabilizing a temperature of a motor. Field-oriented control (FOC) components of input current applied to motor coils of the primary or secondary are defined as a quadrature (Ij) current component generating motion, and a perpendicular, direct (L) current component, generating no motor motion. The control unit may include non-transient memory having instructions that when executed implement a process including applying the Idcurrent component to the motor, setting the motor temperature to a value within a previously determined temperature range. Setting the temperature is understood to mean causing the temperature to reach a level within the target range and / or to maintain the value in the target range. The target range is typically a range calibrated for positioning, that is, the effect of Iq, on the motor motion is calibrated.

[0052] An example 2 of the invention includes the features of example 1 and further includes determining a target power level of current applied to the motor required to reach or to maintain the motor temperature and calculating the Idcurrent component to be applied according to the target power level.

[0053] An example 3 of the invention includes the features of example 2 and further includes determining an Iqcurrent component applied to the motor, wherein calculating the Idcurrent component to be applied according to the target power level includes calculating a target Idpower according to the difference between the target power level and an f, power generated by the Iqcurrent component, and, responsively to the target Idpower, calculating the Idcurrent component.

[0054] An example 4 of the invention includes the features of example 3, where calculating the target Idpower according to the difference between the target power level and the Iqpower includes determining the Iqpower as a time-varying signal according to a time-varyingIqcurrent component required by a pre-set operating routine for motor motion.

[0055] An example 5 of the invention includes the features of example 3, where calculating the target Idpower according to the difference between the target power level and the Iqpower includes measuring a time-varying Iqcurrent component during execution of an operating routine for motor motion, and wherein the method further includes calculating and applying the Idcurrent component in real time to the motor responsively to theIqpower provided by the measured Iqcurrent component.

[0056] An example 6 of the invention includes the features of example 3, where calculating the Idcurrent component according to the target Idpower includes determining a target Idcurrent component from the target Idpower level and filtering the target Idcurrent component by a low-pass filter to generate a smoothed Idcurrent component indicative of a thermal flow rate.

[0057] An example 7 of the invention includes the features of example 6, where calculating the Idcurrent component further includes filtering the smoothed Idcurrentcomponent by a limiter to limit a maximum value of the Idcurrent component.

[0058] An example 8 of the invention includes the features of example 3, where he target power level is an average power over a given period of time.

[0059] An example 9 of the invention includes the features of any of the above examples, where the Idcurrent component is negative to prevent magnetic flux saturation.

[0060] An example 10 of the invention includes the features of any of the above examples, where the previously determined temperature range is a calibrated temperature range at which a relationship between an Iqcurrent component of input current is calibrated with movement of the motor primary.

[0061] An example 11 of the invention includes the features of any of the above examples, where the motor is a permanent-magnet, synchronous linear motor (PMSLM).

[0062] An example 12 of the invention includes the features of any of the above examples, where the motor has a moving motor primary and a fixed motor secondary, and coils receiving the FOC components of input current are either on the moving motor primary or on the fixed motor secondary.

[0063] Further examples of the invention include the methods implemented by the control unit in any of the above examples 1 through 12.

[0064] A further example of the invention is apparatus of a metrology system that includes: one or more processor-controlled motors for moving one or more respective moving primaries according to input currents; and a processor having memory storing instructions that when executed implement a process for stabilizing a temperature of the motor. The process may include the features of any of the examples described above with respect to examples of the control unit and the methods of the present invention.

[0065] In a further example, the one or more motors of the apparatus may control a position of a stage of a metrology system supporting an object under inspection. Additionally, the one or more motors may control a multi-axis stage, having an XY, XYZ, or XYZ-Rotation configuration.

[0066] In summary, examples of the invention provide a method and system for maintaining a stable motor temperature over varying operating applications and load cycles, reducing the time required for positioning corrections. This results in enhanced positioning repeatability, improving the efficiency and accuracy of manufacturing processes that require precision positioning. The method is applicable to a variety of motors, including, but not limited to, single-axis, brushless linear motors and multi-axis stages, such as XY, XYZ, and XYZ-Rotation configurations, with benefits extending to each axis motor, thereby minimizing positioning errors caused by thermal variations and improving overall system performance.

[0067] It is to be understood that the methods and / or processes described herein may be implemented by any one or more software, and / or hardware, element, apparatus, device, mechanism, electronic and / or digital computerized system, unit, processing module, device, machine, engine, etc. The system, module, unit, device etc. or parts thereof, may be programmed to perform particular functions pursuant to computer readable and executable instructions, rules, conditions etc. from programmable hardware and / or software-based execution modules that may implement one or more methods or processes disclosed herein, and therefore can, in effect, be considered as disclosing a “special purpose computer” particular to embodiments of each disclosed method / process.

[0068] Additionally or alternatively, the methods and / or processes disclosed herein may be implemented as a computer program that may be tangibly or intangibly embodiedby a special purpose computer readable signal medium. A computer readable signal medium may include a propagated data signal with computer readable program code (i.e.,“instructions”) embodied therein. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a non-transitory computer or machine-readable storage device and that can communicate, propagate, or transport a program for use by or in connection with apparatuses, systems, platforms, methods, operations and / or processes discussed herein.

[0069] The terms “non-transitory computer-readable storage device” and “non- transitory machine-readable storage device,” referred to herein as processor memory, may also include distribution media, intermediate storage media, execution memory of a computer, and any other medium or device capable of storing for later reading by a computer program implementing embodiments of a method disclosed herein. A computer program product can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by one or more communication networks.

[0070] The computer-readable and executable instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other devices implement the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0071] A module, a device, a mechanism, a unit and or a subsystem may each comprise executable instructions (e.g. commands). A module may be embodied by a circuit or acontroller programmed to cause the system to implement the method, process and / or operation as disclosed herein. For example, a module may be implemented as a hardware circuit including, for example, custom very large-scale integration (VLSI) circuits or gate arrays, an application-specific integrated circuit (ASIC), off-the-shelf semiconductors such as logic chips, transistors, and / or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices and / or the like.

[0072] Methods or processes and / or systems, devices, subsystems, and / or apparatuses etc., disclosed in the description herein are not to be limited strictly to flowcharts and / or diagrams provided in the Drawings. For example, a method may include additional or fewer processes or steps in comparison to what is described in the figures. In addition, embodiments of the method are not necessarily limited to the chronological order as illustrated and described herein. Terms used in the singular shall also include a plural scope, except where expressly otherwise stated or where the context otherwise requires.

[0073] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments or examples, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, example and / or option, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment, example or option of the invention. Certain features described in the context of various embodiments, examples and / or any optional implementation are not to be considered essential features of those embodiments, unless the embodiment, example and / or optional implementation is inoperative without those elements.

[0074] The number of elements shown in the figures should by no means be construed as limiting and is for illustrative purposes only. Throughout this application, various embodiments may be presented in and / or relate to a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the embodiments. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, a description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. Moreover, although the above description discloses a limited number of exemplary embodiments of the invention, these embodiments should not apply any limitation to the scope of the invention, but rather be considered as exemplifications of some of the manners in which the invention can be implemented.

Claims

CLAIMS1. A control unit for stabilizing a temperature of a motor, wherein field-oriented control (FOC) components of input current applied to motor coils of the motor primary or secondary are defined as a quadrature (Iq) current component generating motion, and a perpendicular, direct ( Id) current component, generating no motor motion, the control unit having memory storing instructions that when executed implement the process for stabilizing the motor temperature, the process comprising applying an Idcurrent component to the motor, setting the motor temperature to a value within a previously determined temperature range calibrated for positioning.

2. The control unit of claim 1, further comprising determining a target power level of current applied to the motor required to set the motor temperature and calculating the Idcurrent component to be applied according to the target power level.

3. The control unit of claim 2, further comprising determining an Idcurrent component applied to the motor, wherein calculating the la current component to be applied according to the target power level comprises calculating a target Idpower according to the difference between the target power level and an Iqpower generated by the Iqcurrent component, and responsively to the target Idpower calculating the Idcurrent component.

4. The control unit of claim 3, wherein calculating the target Idpower according to the difference between the target power level and the Iqpower comprises determining the Iqpower as a time-varying signal according to a time-varying Iqcurrent component required by a pre-set operating routine for motor motion.

5. The control unit of claim 3, wherein calculating the target Idpower according to the difference between the target power level and the Iqpower comprises measuring a time-varyingIqcurrent component during execution of an operating routine for motor motion, and wherein the process further comprises calculating and applying the Idcurrent component in real time to the motor responsively to the Iqpower provided by the measured Iqcurrent component.

6. The control unit of claim 3, wherein calculating the Idcurrent component according to the target Idpower comprises determining a target Idcurrent component from the target Idpower level and filtering the target Idcurrent component by a low-pass filter to generate a smoothed Idcurrent component indicative of a thermal flow rate.

7. The control unit of claim 6, wherein calculating the Idcurrent component further comprises filtering the smoothed Idcurrent component by a limiter to limit a maximum value of the Idcurrent component.

8. The control unit of claim 3, wherein the target power level is an average power over a given period of time.

9. The control unit of claim 1, wherein the Idcurrent component is negative to prevent magnetic flux saturation.

10. The control unit of claim 1, wherein the previously determined temperature range is a calibrated temperature range at which a relationship between anIqcurrent component of input current is calibrated with movement of the motor primary.

11. The control unit of claim 1, wherein the motor is a permanent-magnet, synchronous linear motor (PMSLM).

12. The control unit of claim 1, wherein the motor has a moving motor primary and a fixed motor secondary, wherein coils receiving the FOC components of input current are either on the moving motor primary or on the fixed motor secondary.

13. A method for stabilizing a temperature of a motor, wherein field-oriented control (FOC) components of input current applied to motor coils of the motor primary or secondary are defined as a quadrature (Iq) current component generating motion, and a perpendicular, direct ( Id) current component, generating no motor motion, the method comprising applying an Idcurrent component to the motor, setting the motor temperature to a value within a previously determined temperature range calibrated for positioning.

14. The method of claim 13, further comprising determining a target power level of current applied to the motor required to set the motor temperature and calculating the Idcurrent component to be applied according to the target power level.

15. The method of claim 14, further comprising determining an Iqcurrent component applied to the motor, wherein calculating the Idcurrent component to be applied according to the target power level comprises calculating a target Idpower according to the difference between the target power level and an Iqpower generated by the Iqcurrent component, and responsively to the target Idpower calculating the Idcurrent component.

16. The method of claim 15, wherein calculating the target Idpower according to the difference between the target power level and the Iqpower comprises determining the Iqpower as a time-varying signal according to a time-varying Iqcurrent component required by a pre-set operating routine for motor motion.

17. The method of claim 15, wherein calculating the target Idpower according to the difference between the target power level and the Iqpower comprises measuring a timevarying f, current component during execution of an operating routine for motor motion, and wherein the method further comprises calculating and applying the Idcurrentcomponent in real time to the motor responsively to the Iqpower provided by the measured Iqcurrent component.

18. The method of claim 15, wherein calculating the Idcurrent component according to the target Idpower comprises determining a target Idcurrent component from the target Idpower level and filtering the target Idcurrent component by a low-pass filter to generate a smoothed Idcurrent component indicative of a thermal flow rate.

19. The method of claim 18, wherein calculating the Idcurrent component further comprises filtering the smoothed Idcurrent component by a limiter to limit a maximum value of the Idcurrent component.

20. The method of claim 15, wherein the target power level is an average power over a given period of time.

21. The method of claim 13, wherein the Idcurrent component is negative to prevent magnetic flux saturation.

22. The method of claim 13, wherein the previously determined temperature range is a calibrated temperature range at which a relationship between an Iqcurrent component of input current is calibrated with movement of the motor primary.

23. The method of claim 13, wherein the motor is a permanent-magnet, synchronous linear motor (PMSLM).

24. The method of claim 13, wherein the motor has a moving motor primary and a fixed motor secondary, wherein coils receiving the FOC components of input current are either on the moving motor primary or on the fixed motor secondary.

25. Apparatus for positioning, comprising: one or more motors that move one or more respective moving primaries according to input currents, wherein field-oriented control (FOC) components of the input currents are defined as direct ( Id) current component, aligned with the magnetic field of the moving primaries and causing no motor motion, and quadrature ( Iq) current components, perpendicular to the magnetic field of the moving primaries and generating motor motion; and a processor having memory storing instructions that when executed implement a process for stabilizing a temperature of the apparatus, the process including applying an Idcurrent component to the motor, setting the motor temperature at a value within a previously determined temperature range calibrated for positioning.

26. The apparatus of claim 25, wherein the one or more motors control a position of a stage of a metrology system supporting an object under inspection.

27. The apparatus of claim 25, wherein the one or more motors control a multi-axis stage, having one of an XY, XYZ, or XYZ-Rotation configuration.

Images