Method for searching for the zero position of a graticule

Abstract

The application provides a method for searching the zero position of a grating ruler, comprising: providing a measurement system, which comprises a grating ruler and a permanent magnet synchronous motor, the grating ruler comprising a ruler tape and a reading head, the permanent magnet synchronous motor being used to drive the reading head to move on the ruler tape, a plurality of index fringes being arranged on the ruler tape, the reading head being used to output corresponding index pulses when each index fringe is triggered; calibrating the measurement system to obtain a phase angle table, the phase angle table containing index pulses and phase angles corresponding to at least part of the index fringes; moving the reading head until the corresponding phase angle is measured after the initial triggering of an index fringe; finding the index pulse corresponding to the measured phase angle from the phase angle table to determine the position of the index fringe initially triggered by the reading head, and further determine the zero position of the measurement system. The technical scheme of the application can obviously improve the zero searching speed.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method for searching the zero position of a gate ruler. Background Technology

[0002] In photolithography systems, a system consisting of position sensors such as relative grating rulers and motors is used to measure the positions of the workpiece stage and mask stage. After the system is installed, a zero position is defined (usually at the edge of the mechanical limit). However, when the system is powered on, the starting position of the motor and the reading head in the relative grating ruler cannot be guaranteed to be at the zero position. Therefore, after the system is powered on, it is necessary to search for the zero position of the system first.

[0003] The current zero-finding method involves adding a sensor to the edge of the system's mechanical limit. After the linear closed loop, the reading head moves in a fixed direction until the sensor is triggered, simultaneously recording the current stripe count value relative to the grating ruler. This value is then fixedly biased to determine the system's zero position. However, this zero-finding process requires an additional sensor, and the reading head's movement distance is long, making the zero-finding process slow.

[0004] Therefore, improving the speed of zero-finding is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for searching the zero position of a grating ruler, which significantly improves the zero-search speed.

[0006] To achieve the above objective, the present invention provides a method for searching the zero position of a grating ruler, comprising:

[0007] A measurement system is provided, the measurement system including a scale and a permanent magnet synchronous motor, the scale including a scale belt and a reading head, the permanent magnet synchronous motor being used to drive the reading head to move on the scale belt, the scale belt being provided with a plurality of index stripes, the reading head being used to output a corresponding index pulse when each of the index stripes is triggered;

[0008] The permanent magnet synchronous motor is used to find the initial phase angle at the first current position so that the permanent magnet synchronous motor can complete the position loop closure;

[0009] The measurement system is calibrated to obtain a phase angle table, the phase angle table including at least a portion of the index stripes corresponding to the index pulses and phase angles;

[0010] The permanent magnet synchronous motor is used to find the initial phase angle at the second current position so that the permanent magnet synchronous motor can complete the position loop closure;

[0011] Move the reading head until the corresponding phase angle is measured after the index stripe is first triggered;

[0012] The index pulse corresponding to the measured phase angle is found in the phase angle table to determine the position of the index stripe that is initially triggered by the reading head, thereby determining the zero position of the measurement system.

[0013] Optionally, a plurality of counting stripes are arranged at intervals between two adjacent index stripes, and the reading head is used to count the index stripes and the counting stripes.

[0014] Optionally, the length of the index stripe is greater than the length of the counting stripe.

[0015] Optionally, before using the permanent magnet synchronous motor to find the initial phase angle at the first current position and the second current position, the measurement system is powered on, and the stripe count value at the powered-on position is a fixed initial count value.

[0016] Optionally, the initial count value is 0.

[0017] Optionally, the measurement system is calibrated when it is used for the first time.

[0018] Optionally, the steps for calibrating the measurement system include:

[0019] Move the reading head multiple times until it is moved to one end of the tape.

[0020] The reading head is moved between the two ends of the ruler, and during the movement, the corresponding phase angle is measured whenever the index strip is triggered to output the index pulse, so as to obtain the index pulse and the phase angle corresponding to at least a portion of the index strips.

[0021] Optionally, the reading head is moved cyclically between the two ends of the ruler, and the phase angles corresponding to the index stripes at the same positions are averaged.

[0022] Optionally, the reading head is connected to a limiting device to stop the reading head from moving when it reaches both ends of the tape.

[0023] Optionally, at least some of the index stripes may be all of the index stripes within the mechanical travel range of the measuring system.

[0024] Optionally, in the permanent magnet synchronous motor, the distance between two adjacent magnets of the same polarity is a non-integer multiple of the distance between two adjacent index stripes.

[0025] Optionally, for the index stripes at the same location, if the difference between the measured phase angle and the phase angle in the phase angle table exceeds a set error, the measurement system is recalibrated.

[0026] Optionally, the permanent magnet synchronous motor is a linear motor or a rotary motor.

[0027] Optionally, the grating ruler is a relative optical grating ruler or a magnetic grating ruler.

[0028] Compared with the prior art, the zero-position search method of the grating scale of the present invention obtains a phase angle table by calibrating the measurement system. The phase angle table contains index pulses and phase angles corresponding to at least a portion of the index stripes. The reading head is moved until the corresponding phase angle is measured after the index stripe is first triggered. The index pulse corresponding to the measured phase angle is found from the phase angle table to determine the position of the index stripe that was first triggered by the reading head, thereby determining the zero position of the measurement system, which significantly improves the zero-position search speed. Attached Figure Description

[0029] Figure 1 This is a flowchart of a grid ruler zero-position search method according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of a measurement system according to an embodiment of the present invention;

[0031] Figure 3 This is a front view schematic diagram of the reading head on the ruler according to an embodiment of the present invention;

[0032] Figure 4 This is a top view of the reading head on the ruler according to an embodiment of the present invention;

[0033] Figure 5 This is a graph showing the trend of phase angle as the reading head moves along the tape according to an embodiment of the present invention.

[0034] Among them, the appendix Figures 1-5 The annotations in the attached figures are explained as follows:

[0035] 11-Scale stripe; 111-Index stripe; 112-Counting stripe; 12-Reading head; 13-Permanent magnet stator; 131-First magnet; 132-Second magnet; 14-Three-phase coil mover. Detailed Implementation

[0036] To make the objectives, advantages, and features of the present invention clearer, the following provides a more detailed description of the grating ruler zero-position search method proposed in this invention. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly illustrate the objectives of the embodiments of the present invention.

[0037] One embodiment of the present invention provides a method for searching the zero position of a grating ruler, see reference. Figure 1 , Figure 1This is a flowchart of a grid ruler zero-position search method according to an embodiment of the present invention, from... Figure 1 As can be seen from this, the method for searching the zero position of the grating ruler includes:

[0038] Step S1, a measurement system is provided, the measurement system includes a scale and a permanent magnet synchronous motor, the scale includes a scale belt and a reading head, the permanent magnet synchronous motor is used to drive the reading head to move on the scale belt, the scale belt is provided with multiple index stripes, and the reading head is used to output a corresponding index pulse when each index stripe is triggered;

[0039] Step S2: The permanent magnet synchronous motor is used to find the initial phase angle at the first current position so that the permanent magnet synchronous motor can complete the position loop closure.

[0040] Step S3: Calibrate the measurement system to obtain a phase angle table, the phase angle table containing at least a portion of the index stripes corresponding to the index pulses and phase angles;

[0041] Step S4: The permanent magnet synchronous motor is used to find the initial phase angle at the second current position so that the permanent magnet synchronous motor can complete the position loop closure.

[0042] Step S5: Move the reading head until the corresponding phase angle is measured after the index stripe is triggered for the first time;

[0043] Step S6: Find the index pulse corresponding to the measured phase angle from the phase angle table to determine the position of the index stripe that is initially triggered by the reading head, and then determine the zero position of the measurement system.

[0044] See below. Figures 2-5 A more detailed description of the grating ruler zero-position search method provided in this embodiment:

[0045] Follow step S1, refer to Figures 2-4 A measurement system is provided, the measurement system including a scale and a permanent magnet synchronous motor. The scale includes a scale belt 11 and a reading head 12. The permanent magnet synchronous motor is used to drive the reading head 12 to move on the scale belt 11. The scale belt 11 is provided with a plurality of index stripes 111. The reading head 12 is used to output a corresponding index pulse when each of the index stripes 111 is triggered.

[0046] On the ruler 11, a plurality of counting stripes 112 are arranged at intervals between two adjacent index stripes 111. The reading head 12 is also used to count the index stripes 111 and the counting stripes 112. When the reading head 12 triggers each counting stripe 112, it can also output a corresponding counting pulse. The index pulse and the counting pulse are different detection signals.

[0047] Specifically, the reading head 12 triggers the index stripe 111 when it moves to the position of the index stripe 111, and triggers the counting stripe 112 when it moves to the position of the counting stripe 112.

[0048] The length of the index stripe 111 is greater than the length of the counting stripe 112, and the spacing between two adjacent index stripes 111 is equal, the spacing between two adjacent counting stripes 112 is equal, and the spacing between each index stripe 111 and an adjacent counting stripe 112 is equal to the spacing between two adjacent counting stripes 112. By using the reading head 12 to count the index stripes 111 and / or the counting stripes 112, the relative position of the reading head 12 on the ruler 11 (i.e., the distance the reading head 12 has moved on the ruler 11) can be obtained.

[0049] The grating ruler can be a relative optical grating ruler or a magnetic grating ruler, etc., and the magnetic grating ruler only has relative position. If the grating ruler is a relative optical grating ruler, then the index stripe 111 and the counting stripe 112 are light-induced stripes, and the index pulse and the counting pulse are optical signals; if the grating ruler is a magnetic grating ruler, then the index stripe 111 and the counting stripe 112 are magnetically induced stripes, and the index pulse and the counting pulse are magnetic signals.

[0050] The permanent magnet synchronous motor can be a linear motor or a rotary motor; when the permanent magnet synchronous motor is a rotary motor, the permanent magnet synchronous motor is stationary at a certain specified angle.

[0051] like Figure 2 As shown, the permanent magnet synchronous motor may include a permanent magnet stator 13 and a three-phase coil mover 14. In the permanent magnet stator 13, a first magnet 131 and a second magnet 132 with opposite polarities are arranged alternately. When the polarity of the first magnet 131 is the S pole, the polarity of the second magnet 132 is the N pole; when the polarity of the first magnet 131 is the N pole, the polarity of the second magnet 132 is the S pole. In other embodiments, the permanent magnet synchronous motor may also include a permanent magnet mover and a three-phase coil stator.

[0052] Furthermore, in the permanent magnet synchronous motor, the distance between two adjacent magnets of the same polarity is a non-integer multiple of the distance between two adjacent index stripes 111, that is, the distance between two adjacent first magnets 131 is a non-integer multiple of the distance between two adjacent index stripes 111, and the distance between two adjacent second magnets 132 is a non-integer multiple of the distance between two adjacent index stripes 111.

[0053] For example, when the distance between two adjacent index stripes 111 is 25mm, the distance between two adjacent first magnets 131 and the distance between two adjacent second magnets 132 cannot be an integer multiple of 25mm (e.g., not 25mm, 50mm, 75mm, etc.), but can be a non-integer multiple of 25mm (e.g., 57mm, etc.).

[0054] The measurement system may further include a digital signal processor (not shown) and a power amplifier (not shown). The operation of the measurement system includes: the reading head 12 transmitting its relative position information on the scale 11 to the digital signal processor; the digital signal processor outputting a theoretical three-phase current (digital or analog signal) to the power amplifier based on the received relative position information; the power amplifier converting the theoretical three-phase current into an actual three-phase current (physical signal) and transmitting it to the permanent magnet synchronous motor; and the permanent magnet synchronous motor driving the reading head 12 to move on the scale 11 based on the received actual three-phase current.

[0055] The digital signal processor (DSP) may include various microprocessors (MCUs), programmable logic controllers (PLCs), and industrial control computers, etc.; the power amplifier (PA) may be a current loop module.

[0056] When the reading head 12 samples its relative position on the scale 11, a fixed-time sampling control method can be adopted. The sampling time is, for example, 2.5 kHz (the sampling time can be adjusted according to the accuracy of the scale and the processing speed of the digital signal processor), and the sampling period is, for example, 400 μs. That is, the relative position of the reading head 12 on the scale 11 is updated once every 400 μs. The updated relative position information is transmitted to the digital signal processor. The digital signal processor calculates the phase angle based on the received updated relative position information and sends the phase angle to the power amplifier. The power amplifier outputs to the permanent magnet synchronous motor, causing the permanent magnet synchronous motor to move.

[0057] After the measurement system is installed, the zero point of the measurement system will also be defined. The zero point can be located at any position on the ruler 11 (for example, at both ends or in the middle area of ​​the ruler 11).

[0058] Since the initial absolute position of the reading head 12 on the scale 11 needs to be the same and known each time the measurement system starts running, but currently the current absolute position of the reading head 12 on the scale 11 is different and unknown each time the measurement system is powered on (because the position where the reading head 12 stops on the scale 11 is different and unknown after the measurement system finishes running in different times), the current insulation position of the reading head 12 at the moment of power-on cannot be used as the initial absolute position for starting operation. Therefore, in order to ensure the accuracy of each measurement, the zero position is used as the initial absolute position for starting the measurement system each time (to ensure that the initial absolute position is the same each time it runs). Therefore, the zero position needs to be searched before each operation of the measurement system to move the reading head 12 from the current absolute position at the moment of power-on to the zero position on the scale 11 before starting the measurement system.

[0059] According to step S2, the permanent magnet synchronous motor is used to find the initial phase angle at the first current position. After the search for the initial phase angle is completed, the permanent magnet synchronous motor completes the position loop closure.

[0060] Before using the permanent magnet synchronous motor to find the initial phase angle at the first current position, the measurement system is powered on. At this time, the power-on position is the first current position, and the stripe count value at the power-on position is a fixed initial count value.

[0061] Preferably, the initial count value is 0. Subsequently, as the reading head 12 moves on the ruler 11, the stripe count value is incremented by 1 each time an index stripe 111 and a counting stripe 112 are triggered. It should be noted that in other embodiments, the initial count value may not be 0. In this case, a bias can be uniformly added so that the stripe count value at the power-on position after the bias is 0, to facilitate subsequent calculations.

[0062] According to step S3, the measurement system is calibrated to obtain a phase angle table, which contains the index pulse and phase angle corresponding to at least a portion of the index stripes. That is, the phase angle table characterizes the index pulse and phase angle corresponding to at least a portion of the index stripes 111 on the scale 11.

[0063] The phase angle table can be saved as a parameter to the digital signal processor.

[0064] Since the stripe count value at the power-on position is 0, during the calibration of the measurement system, as the reading head 12 moves on the scale 11, the stripe count value increases by 1 each time the reading head 12 triggers an index stripe 111, causing the count value of the index stripe 111 to accumulate continuously.

[0065] Preferably, the measurement system is calibrated upon initial use to obtain a phase angle table, enabling rapid retrieval of the zero point on subsequent uses. In other embodiments, the measurement system may be calibrated periodically to ensure the accuracy of the phase angle table.

[0066] The calibration steps of the measurement system may include: First, starting from the first current position, moving the reading head 12 multiple times, with each movement being a very short distance, until the reading head 12 is moved to one end of the ruler 11 (e.g., the leftmost end of the ruler 11). It should be noted that during this process, the index pulses and phase angles corresponding to the index stripes 111 triggered by the reading head 12 are not included in the phase angle table. Then, the reading head 12 is moved between the two ends of the ruler 11 at a low and uniform speed. During the movement, whenever the index stripe 111 is triggered to output the index pulse, the corresponding phase angle is measured to obtain the index pulses and phase angles corresponding to at least a portion of the index stripes 111, thereby obtaining the phase angle table.

[0067] Preferably, in the step of calibrating the measurement system, the reading head 12 is moved cyclically between the two ends of the ruler 11. After obtaining the index pulse and phase angle corresponding to the index stripe 111 at at least some positions on the ruler 11, the phase angles corresponding to the index stripe 111 at the same position are averaged and used as the phase angle in the phase angle table, so that the phase angle in the phase angle table is more accurate.

[0068] In one embodiment of the present invention, the reading head 12 can be moved from one end of the ruler 11 to the other end of the ruler 11 (e.g., the rightmost end of the ruler 11) as an example. During the movement, whenever the index strip 111 is triggered to output the index pulse, the corresponding first phase angle is measured, and the triggered index strips 111 are counted to record the index pulse and the first phase angle corresponding to at least a portion of the index strips 111 on the ruler 11. That is, each position of the index strip 111 on the ruler 11 has a corresponding index pulse and a first phase angle. Then, the reading head 12 is moved from the other end of the ruler 11 to the rightmost end of the ruler 11. At one end, during the movement, whenever the index stripe 111 is triggered to output the index pulse, the corresponding second phase angle is measured, and the triggered index stripe 111 is counted to record the index pulse and second phase angle corresponding to at least a portion of the index stripes 111 on the ruler 11 again, that is, each position of the index stripe 111 on the ruler 11 has a corresponding index pulse and second phase angle; then, the first phase angle and the second phase angle corresponding to the index stripe 111 at the same position on the ruler 11 are averaged to obtain the index pulse and the phase angle corresponding to at least a portion of the index stripes 111 on the ruler 11.

[0069] In another embodiment, the first phase angle can also be directly used as the phase angle in the phase angle table.

[0070] like Figure 5 As shown, taking the movement of the reading head 12 from the leftmost end of the ruler 11 to the rightmost end of the ruler 11 as an example, curve L1 is the curve of the phase angle (in rad) as the reading head 12 moves a distance (in m) on the ruler 11. Each straight line L2 represents the phase angle corresponding to the triggering of each index stripe 111. The phase angles corresponding to the index stripes 111 at different positions are different.

[0071] In the permanent magnet synchronous motor, since the distance between two adjacent magnets of the same polarity is a non-integer multiple of the distance between two adjacent index stripes 111, the commutation phase angle of each magnet is different, thereby enabling the realization of… Figure 5 The phase angles corresponding to the index stripes 111 at different positions on the scale 11 are different, which makes it possible to quickly determine which index stripe 111 the reading head 12 is currently located on the scale 11 based on the phase angle in the phase angle table, that is, to determine the current absolute position of the reading head 12 on the scale 11.

[0072] In addition, the reading head 12 is connected to a limiting device to stop the reading head 12 when it moves to both ends of the scale 11 (i.e., one end and the other end), so as to prevent the reading head 12 from falling off the scale 11 or hitting the two ends of the scale 11, thereby ensuring the safety of the measurement system.

[0073] Furthermore, since the permanent magnet synchronous motor and the reading head 12, etc., have mechanical travel limitations in the measurement system, and the length of the scale 11 is designed to be greater than the mechanical travel that the permanent magnet synchronous motor and the reading head 12, etc., can reach the index stripes 111 on the scale 11 that are outside the mechanical travel range of the measurement system, in step S3, at least some of the index stripes 111 are all the index stripes 111 within the mechanical travel range of the measurement system, so that the reading head 12 can trigger all the index stripes 111 on the scale 11 that are within the mechanical travel range of the measurement system, thereby making the phase angle table contain the index pulses and phase angles corresponding to all the index stripes 111 within the mechanical travel range of the measurement system.

[0074] According to step S4, the permanent magnet synchronous motor is used to find the initial phase angle at the second current position. After the initial phase angle is found, the permanent magnet synchronous motor completes the position loop closure.

[0075] Both the first current position and the second current position can be any position on the ruler 11, and the second current position can be the same as or different from the first current position.

[0076] Before using the permanent magnet synchronous motor to find the initial phase angle at the second current position, the measurement system is powered on. At this time, the powered-on position is the second current position, and the stripe count value at the powered-on position is a fixed initial count value.

[0077] Preferably, the initial count value is 0. Subsequently, as the reading head 12 moves on the ruler 11, the stripe count value is incremented by 1 each time an index stripe 111 and a counting stripe 112 are triggered. It should be noted that in other embodiments, the initial count value may not be 0. In this case, a bias can be uniformly added so that the stripe count value at the power-on position after the bias is 0, to facilitate subsequent calculations.

[0078] According to step S5, the reading head 12 is moved from the second current position until the index stripe 111 is triggered for the first time to output the corresponding index pulse, and then the digital signal processor measures the corresponding phase angle.

[0079] According to step S6, the index pulse corresponding to the phase angle measured in step S5 is found from the phase angle table to determine the position of the index stripe 111 that the reading head 12 is initially triggered, that is, the position of the reading head 12 at which index stripe 111 on the scale 11 can be determined, so that the current absolute position of the reading head 12 on the scale 11 is determined.

[0080] Since the position of the zero point on the scale 11 is known, after the current absolute position of the reading head 12 on the scale 11 at the moment of power-on is determined by the phase angle table, the distance between the reading head 12 and the zero point is also known, thus enabling the zero point of the measurement system to be quickly found.

[0081] In this invention, since the reading head 12 moves from the power-on position to the initial triggering of the index strip 111, the current absolute position of the reading head 12 on the scale 11 can be determined according to the phase angle table, thereby completing the zero-searching process. This ensures that the distance the reading head 12 moves during the entire zero-searching process does not exceed the spacing between two adjacent index stripes 111. Compared with the zero-searching method of adding a sensor at the edge of the mechanical limit of the system, the zero-searching method of this invention significantly reduces the moving distance of the reading head 12, thereby significantly improving the zero-searching speed. The initialization of the entire system is faster, and no additional sensors or other components are required.

[0082] Furthermore, under any operating condition, if the difference between the measured phase angle and the corresponding phase angle in the phase angle table for the same index stripe at any position exceeds a set error, the grating ruler is determined to be contaminated. The measurement system can then be recalibrated to ensure the accuracy of the phase angle table. Moreover, since contamination of the grating ruler can cause abnormal commutation of the permanent magnet synchronous motor, recalibrating the measurement system improves its reliability, thereby enhancing product quality.

[0083] In summary, the zero-position search method for a grating scale provided by the present invention includes: providing a measurement system, the measurement system including a grating scale and a permanent magnet synchronous motor, the grating scale including a scale belt and a reading head, the permanent magnet synchronous motor driving the reading head to move on the scale belt, the scale belt being provided with multiple index stripes, the reading head being used to output a corresponding index pulse when each index stripe is triggered; using the permanent magnet synchronous motor to find an initial phase angle at a first current position, so that the permanent magnet synchronous motor completes the position loop closure; calibrating the measurement system to obtain a phase angle table, the phase angle table including the index pulses and phase angles corresponding to at least a portion of the index stripes; using the permanent magnet synchronous motor to find an initial phase angle at a second current position, so that the permanent magnet synchronous motor completes the position loop closure; moving the reading head until the corresponding phase angle is measured after the index stripe is first triggered; finding the index pulse corresponding to the measured phase angle from the phase angle table to determine the position of the index stripe initially triggered by the reading head, thereby determining the zero position of the measurement system. The zero-position search method of the grating ruler of the present invention significantly improves the zero-search speed.

[0084] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for searching the zero position of a grating ruler, characterized in that, include: A measurement system is provided, the measurement system including a scale and a permanent magnet synchronous motor, the scale including a scale belt and a reading head, the permanent magnet synchronous motor being used to drive the reading head to move on the scale belt, the scale belt being provided with a plurality of index stripes, the reading head being used to output a corresponding index pulse when each of the index stripes is triggered; The permanent magnet synchronous motor is used to find the initial phase angle at the first current position so that the permanent magnet synchronous motor can complete the position loop closure; The measurement system is calibrated to obtain a phase angle table, the phase angle table including at least a portion of the index stripes corresponding to the index pulses and phase angles; The permanent magnet synchronous motor is used to find the initial phase angle at the second current position so that the permanent magnet synchronous motor can complete the position loop closure; Move the reading head until the corresponding phase angle is measured after the index stripe is first triggered; The index pulse corresponding to the measured phase angle is found from the phase angle table to determine the position of the index stripe that is initially triggered by the reading head, thereby determining the zero position of the measurement system.

2. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, Multiple counting stripes are arranged at intervals between two adjacent index stripes, and the reading head is used to count the index stripes and the counting stripes.

3. The method for searching the zero position of the grating ruler as described in claim 2, characterized in that, The length of the index stripe is greater than the length of the counting stripe.

4. The method for searching the zero position of the grating ruler as described in claim 2, characterized in that, Before using the permanent magnet synchronous motor to find the initial phase angle at the first current position and the second current position, the measurement system is powered on, and the stripe count value at the powered-on position is a fixed initial count value.

5. The method for searching the zero position of the grating ruler as described in claim 4, characterized in that, The initial count value is 0.

6. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, When using the measurement system for the first time, calibrate the measurement system.

7. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, The steps for calibrating the measurement system include: Move the reading head multiple times until it is moved to one end of the tape. The reading head is moved between the two ends of the ruler, and during the movement, the corresponding phase angle is measured whenever the index strip is triggered to output the index pulse, so as to obtain the index pulse and the phase angle corresponding to at least a portion of the index strips.

8. The method for searching the zero position of the grating ruler as described in claim 7, characterized in that, The reading head is moved cyclically between the two ends of the ruler, and the phase angles corresponding to the index stripes at the same positions are averaged.

9. The method for searching the zero position of the grating ruler as described in claim 7, characterized in that, The reading head is connected to a limiting device to stop the reading head from moving when it reaches both ends of the tape.

10. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, The at least some of the index stripes are all the index stripes within the mechanical travel range of the measuring system.

11. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, In the permanent magnet synchronous motor, the distance between two adjacent magnets of the same polarity is a non-integer multiple of the distance between two adjacent index stripes.

12. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, If the difference between the measured phase angle and the phase angle in the phase angle table exceeds the set error for the index stripe at the same position, the measurement system shall be recalibrated.

13. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, The permanent magnet synchronous motor is either a linear motor or a rotary motor.

14. The method for searching the zero position of the grating ruler as described in claim 1, characterized in that, The grating ruler is a relative optical grating ruler or a magnetic grating ruler.

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