CN109916315B - Measuring device based on separation type grating - Google Patents
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Abstract
The invention provides a measuring device based on a separated grating, which comprises a control module, a base, a plane moving platform, a grating rigid body, grating reading heads and measuring heads, wherein the grating rigid body is provided with perforations, the measuring heads and the grating surface of the grating rigid body are positioned on the same plane, the grating rigid body is provided with more than two groups of grating line groups, the grating line groups comprise a plurality of grating lines which are parallel to each other and are sequentially arranged at equal intervals, the number of the grating reading heads is the same as that of the grating line groups, the grating reading heads are in one-to-one correspondence with the grating line groups, and the connecting lines between the measuring heads and the grating reading heads are perpendicular to the grating lines in the grating line groups corresponding to the grating reading heads. The invention realizes zero Abbe error design, has relatively low requirement on the precision of the guide element and relatively low cost; meanwhile, the environmental adaptability is strong, and the application range is relatively wide.
Description
Technical Field
The invention relates to a measuring device, in particular to a measuring device based on a separation type grating.
Background
In order to realize high-precision displacement measurement, zero abbe error design is a non-negligible concept, and zero abbe error (namely abbe principle) is a long-history design principle in the field of instrumentation, which requires that a measurement line and a reading line coincide, namely an abbe arm is zero, otherwise, the abbe error exists.
The traditional two-dimensional or three-dimensional measuring device generally adopts a grating as a displacement sensor, when a platform moves, the grating moves along with the displacement sensor, the whole coordinate system cannot be kept constant, the coordinate axis cannot always pass through measuring points of a measuring head, the distance between the two measuring points is always changed, the design of the Abbe arm is required to reduce the angle deflection in the movement as much as possible, and therefore, the linearity and the planeness of a mechanical guide element (such as a linear guide rail and the like) are required to be extremely high, and the cost is relatively high.
In the field of precision metering, in order to realize zero Abbe error design, a laser interference technology is a widely applied solution. The laser interferometer uses a laser beam emitted from a laser with a constant position to form a constant coordinate system. By tracking the plane target mirror attached to the moving platform in the direction of the laser optical axis, high-precision measurement of triaxial displacement can be realized, however, the laser interference system has extremely high environmental requirements and extremely sensitive to changes of temperature, air flow and air density, so that the laser interference technology needs an expensive environmental control cavity, on-line measurement is difficult to realize, and the application range is relatively narrow.
In view of this, the present applicant has conducted intensive studies on a measuring device capable of realizing zero abbe error, and has produced the present invention.
Disclosure of Invention
The invention aims to provide a measuring device based on a split grating, which has relatively low cost and relatively wide application range.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the utility model provides a measuring device based on disconnect-type grating, includes control module, base, horizontal sliding connection be in plane moving platform on the base, fixed connection be in grating rigid body on the plane moving platform and respectively fixed connection be in grating reading head and gauge head on the base, the perforation has been seted up on the grating rigid body, the gauge head is located in the perforation and with the bars face of grating rigid body is located the coplanar, be provided with the grid line group of more than two sets of on the grating rigid body, the grid line group includes the grid line that many mutual parallels and equidistant arrange in proper order, the number of grating reading head with the number of grid line group is the same, each grating reading head with each grid line group one-to-one arranges, just the gauge head with the connecting wire between the grating reading head be in the projection on the rigid body of grating and with the grid line in the grid line group that this grating reading head corresponds is arranged perpendicularly, gauge head and each grating reading head respectively with control module communication is connected.
As an improvement of the invention, the plane moving platform is vertically and slidably connected with a lifting table positioned below the grating surface of the grating rigid body, the lifting table is slidably connected with a group of grating line groups, and the grating line groups are vertically and slidably connected with the base.
As an improvement of the invention, two groups of grid line groups are arranged on the grating rigid body, and the grid lines in the two groups of grid line groups are mutually perpendicular.
As an improvement of the invention, the planar moving platform is provided with the first sensors for detecting the motion coupling errors of the lifting platform, the first sensors are in two pairs, and the two first sensors in each pair are symmetrically arranged with the center line of the table top of the lifting platform as the center.
As an improvement of the invention, the base is provided with a large displacement driver and a micro displacement driver for driving the plane moving platform to move.
As an improvement of the invention, the large displacement driver is a stepping motor, and the micro displacement driver is a piezoelectric ceramic driver.
As an improvement of the invention, the grating reading head comprises a laser emitter, a first light-splitting element for receiving the double-frequency laser emitted by the laser emitter, a first coherent module and a polarization light-splitting element which are respectively used for receiving the light beams emitted by the first light-splitting element, a reflecting mirror which is used for reflecting the light beams emitted by the polarization light-splitting element to the corresponding grating line group, a second coherent module matched with the polarization light-splitting element, and a calculation comparison module which is respectively connected with the first coherent module and the second coherent module.
As an improvement of the invention, after the expected displacement information is input into the control module, the control module sends control information to the large displacement driver and/or the micro displacement driver according to the expected displacement information, the large displacement driver and/or the micro displacement driver drives the plane moving platform to slide relative to the base according to the control information, meanwhile, the measuring head feeds back the actual displacement information of the plane moving platform to the control module, and the control module sends correction information to the large displacement driver and/or the micro displacement driver according to the actual displacement information, and the large displacement driver and/or the micro displacement driver continuously drives the plane moving platform to slide relative to the base according to the correction information.
As an improvement of the invention, the control module is provided with a database, the expected displacement information and the correction information corresponding to the expected displacement information are input into the database, and the control module receives the expected displacement information, then retrieves the correction information from the database and sends the correction information as control information to the large displacement driver and/or the micro displacement driver as feedforward error compensation information.
By adopting the technical scheme, the invention has the following beneficial effects:
1. according to the invention, more than two groups of grating line groups are arranged on the grating rigid body, and the grating reading head and the measuring head are fixedly connected to the base, so that zero Abbe error design is realized, the requirement on the precision of the guide element is relatively low, and the cost is relatively low; meanwhile, the environmental adaptability is strong, and the application range is relatively wide.
2. By high-precision closed-loop motion control, an approximately ideal motion track is realized, a virtual geometric standard is realized, and the dependence of the measurement field on a high-precision physical entity is reduced.
Drawings
FIG. 1 is a schematic diagram of a measuring apparatus in an embodiment;
FIG. 2 is a schematic illustration of the mating structure of the grating cylinder and grating read head in an embodiment;
FIG. 3 is a schematic diagram of a closed loop control flow in an embodiment;
FIG. 4 is a schematic diagram of the optical path structure of a grating reading head according to an embodiment;
FIG. 5 is a schematic view of the optical path structure of another grating reading head according to the embodiment;
fig. 6 is a schematic diagram of the optical path structure of a grating reading head according to another embodiment.
Parts are omitted from the upper drawing, and the corresponding marks in the drawing are as follows:
10-a base; 20-a planar mobile platform;
21-a first sensor; 30-grating rigid body;
31-perforating; 32-gate line groups;
40-grating reading head; 41-a laser emitter;
42-a first light splitting element; 43-a first coherence module;
44-a polarizing beam splitter; 45-reflecting mirror;
46-a second coherent module; 47-a calculation comparison module;
a 48-lambda/4 wave plate; 50-lifting platform;
51-panel; 61-half wave plate;
62-a photodetector 63-a right angle prism;
64-parallelogram prism; 65-depolarizing beam splitter prism.
Detailed Description
The invention is further described with reference to specific examples below:
as shown in fig. 1 to 6, the present embodiment provides a measuring device based on a split grating, which may be used as a two-dimensional measuring device or a three-dimensional measuring device, and when it is used as a two-dimensional measuring device, a lifting table 50, which will be mentioned below, may not be provided.
The measuring device provided in this embodiment includes a control module (not shown in the figure), a base 10, a planar moving platform 20 horizontally slidably connected to the base 10, a grating rigid body 30 fixedly connected to the planar moving platform 20, and a grating reading head 40 and a measuring head (not shown in the figure) respectively fixedly connected to the base 10, wherein the base 10 has a bracket (not shown in the figure) above the grating rigid body 30, and the measuring head is fixedly connected to the bracket. The planar moving platform is a moving platform used in a conventional three-dimensional measuring device, such as a cross sliding table, and is not an important point of the present embodiment, and will not be described in detail herein. In addition, the stylus and each grating reading head 40 are each communicatively coupled to a control module for communicating information, and of course, the control module is a system used in conventional measuring devices and will not be described in detail herein.
The grating rigid body 30 is an integrated flat plate structure, and is arranged in parallel with the table surface of the plane moving platform 20, and the grating rigid body 30 is provided with a perforation 31, which is preferably a square hole and is positioned in the middle of the grating rigid body 30; the grating rigid body 30 is provided with more than two groups of grating lines 32, each grating line group 32 comprises a plurality of grating lines which are parallel to each other and are sequentially arranged at equal intervals, the grating lines 32 are preferably positioned at the edge of the grating rigid body 30 or are positioned close to the edge of the grating rigid body 30, and each group of grating lines 32 respectively forms a rectangular area which can be arranged on the grating rigid body 30 by adopting a conventional mechanical painting technology or a holographic technology. The side of the rigid grating body 30 on which the grating line groups 32 are provided is a grating surface, and in this embodiment, two groups of grating line groups 32 are provided on the rigid grating body 30, and in this embodiment, the grating surface of the rigid grating body 30 is a lower surface thereof, that is, the grating surface faces downward.
The stylus is a stylus used in a conventional grating three-dimensional measuring device, and is located in the through hole 31 and is located on the same plane as the grating surface of the grating rigid body 30. The number of grating reading heads 40 is the same as that of the grating line groups 32, each grating reading head 40 is arranged in one-to-one correspondence with each grating line group 32, and in this embodiment, one grating reading head 40 is arranged right under each grating line group 32 on the grating rigid body 30. The projection of the line between the probe and any of the above-mentioned grating heads 40 on the grating surface of the grating rigid body 30 (i.e., the measuring axis, i.e., various displacement measuring lines) is arranged vertically to the grating lines in the grating line group 32 corresponding to the grating head 40, so that it is ensured that each axis measuring line intersects with the measuring point of the probe, and a stationary coordinate system can be formed, which does not change when the planar moving platform 20 or a lifting platform to be mentioned later moves. Preferably, in this embodiment, the grid lines in the two groups of grid lines 32 located on the rigid grating body 30 are arranged perpendicular to each other, where the length direction of the grid line in one group of grid lines 32 is the X-axis direction, the grating reading head 40 corresponding to the grid line group 32 is called the Y-axis reading head, the length direction of the grid line in the other group of grid lines 32 is the Y-axis direction, the grating reading head 40 corresponding to the grid line group 32 is called the X-axis reading head, and the measuring head, the corresponding grid line group 32, the Y-axis reading head and the X-axis reading head together form a split two-bit grating interferometer.
When the plane moving platform 20 moves along the X-axis direction, the incident light spot of the X-axis reading head moves across the grid line to generate periodic sine wave signals, and the X-axis movement displacement of the platform can be measured by counting and subdividing the sensing direction of the signals through the control module; meanwhile, an incident light spot of the Y-axis reading head moves along a grating line on a corresponding grating, so that a sine wave signal cannot be generated, namely a measuring line of the Y-axis reading head cannot move; the situation is vice versa when the planar mobile platform 20 moves along the Y-axis, thus conforming to the precondition of zero abbe error, where the coordinate system is constant.
In order to realize three-dimensional measurement, in this embodiment, a lifting platform 50 located below the grid surface of the rigid grating body 30 is vertically and slidably connected to the planar moving platform 20, specifically, a mounting hole is formed in the planar moving platform 20 at a position corresponding to the through hole 31, and the lifting platform 50 is disposed in the mounting hole. A group of grid line groups 32 are slidably connected to the lifting table 50, the grid line groups 32 are vertically slidably connected to the base 10, and grid lines in the grid line groups 32 are all arranged parallel to the grid surface of the rigid grating body 30. Specifically, the grating line set 32 is disposed on a panel 51, the panel 51 is simultaneously slidably connected to the lifting platform 50 and the base 10, the bottom of the panel is an approximately ideal plane with high flatness, and of course, the base 10 is also provided with a grating reading head 40, i.e. a Z-axis reading head, which is disposed corresponding to the grating line set 32, and the measuring head, the corresponding grating line set 32 and the Z-axis reading head together form a set of one-dimensional grating interferometers. In addition, the grating line group 32 is located right below the measuring head, and the arrangement direction of the grating lines is the Z axis direction (i.e. the vertical direction), so that the intersection of the measuring lines of the Z axis and the measuring lines of other axes can be ensured to be at the measuring point of the measuring head, so as to realize zero abbe error design.
When the device is used, a measured piece is placed on the table top of the lifting table, when the plane moving platform 20 drives the lifting table 50 to move on the horizontal plane, the panel 51 and the grid line group 32 on the panel slide relative to the lifting table 50, when the lifting table 50 moves up and down, the panel 51 and the grid line group 32 on the panel can slide up and down under the driving of the lifting table 50, at the moment, an incident light spot of the Z-axis reading head moves across the grid line to generate a periodic sine wave signal, and other reading heads cannot generate sine wave signals.
Preferably, in order to eliminate the kinematic coupling error existing in the measurement device, in this embodiment, the planar moving platform 20 is provided with a first sensor 21 for detecting the kinematic coupling error of the lifting platform 50, and specifically, the first sensor 21 is used for detecting the kinematic coupling error of the lifting platform 50 (i.e. the Z axis) occurring in the X axis and Y axis directions when the lifting platform moves, and the kinematic coupling error occurring in the Z axis direction can be directly measured by the Z axis reading head. The first sensors 21 are commercially available displacement sensors, such as an inductance micro sensor, an astigmatism sensor, a confocal sensor or an eddy current sensor, and the like, and are all in communication connection with the control module, wherein two pairs of the first sensors 21 are provided, and two pairs of the first sensors 21 are two, that is, four first sensors 21, and two first sensors 21 in each pair of the first sensors are symmetrically arranged with a center line of the table top of the lifting table 50 in an initial state (that is, a state before measurement), the displacement of which is zero can be set by the control module, because the table top of the lifting table 50 is a plane, it has two centerlines (centerlines in the width direction and the length direction), the symmetrical centerlines of the two pairs of first sensors are the center lines of the table surface of the lifting table 50, taking one pair of first sensors as an example and taking the Y axis as an example, when the X axis displacement is 0, the readings of the two first sensors 21 are all zero, and when at a certain position (X1, Y1, z 1), the readings of the two first sensors 21 are respectively Δ1 and Δ2, and the distance between the two first sensors 21 is D, the motion coupling error occurring on the X axis is Δ below the following relationship:
it can be derived that:
the control module measures and corrects the coupling error according to the motion coupling error delta. It should be noted that, each axis of the planar moving platform 20 (i.e. each moving direction needs to be provided with two first sensors 21 symmetrically arranged with each other), and in addition, the above-mentioned decoupling structure requires that the receiving portion (such as a plane mirror) of the sensor has higher precision, and the present optical preparation process can achieve nano-scale precision, and has low cost, so that the introduction of the sensor does not bring about significant improvement of cost and assembly difficulty.
The driving manner of the planar moving platform 20 can be a conventional manner, such as hand pushing. Preferably, the base 10 is provided with a large displacement driver and a micro displacement driver (both not shown) for driving the movement of the flat moving platform 20, i.e., each movement direction (i.e., X-axis movement and Y-axis movement in the present embodiment) of the flat moving platform 20 is driven by both the large displacement driver and the micro displacement driver, so that rapid movement and fine adjustment are achieved. The specific type and model of the driver can be selected from the market according to actual needs, and in the embodiment, the large displacement driver is a stepping motor, and the micro displacement driver is a piezoelectric ceramic driver. Likewise, the lift table 50 is also driven by a large displacement drive and a micro displacement drive, which are not repeated here. Of course, each of the large displacement driver and the micro displacement driver is connected with a one-to-one fit of the large displacement controller or the micro displacement controller.
The measuring device provided in this embodiment further has a closed-loop control system, for example, as shown in fig. 3, and referring to fig. 1 and 2, the implementation manner of the closed-loop control system is as follows: after inputting the desired displacement information (i.e., the movement track of the desired planar mobile platform 20, the content of the information may be a straight line, a circle or other tracks) into the control module, the control module sends control information to each large displacement driver and/or each micro displacement driver through the large displacement controller or the micro displacement controller according to the desired displacement information (if one driver is not required to work, the corresponding controller will not receive a control signal, i.e., the action of not receiving the control signal is an information); each large displacement driver and/or micro displacement driver drives the plane moving platform 20 to slide relative to the base 10 according to the control information, in the process, motion coupling and external interference (such as friction force, environmental disturbance and the like) can exist, and the moving precision can be influenced, so that the measuring head feeds back the actual displacement information of the plane moving platform 20 to the control module by using the separated two-position grating interferometer while sliding, the control module sends correction information to the large displacement driver and/or micro displacement driver according to the actual displacement information, and the large displacement driver and/or micro displacement driver continuously drives the plane moving platform 20 to slide relative to the base 10 according to the correction information, so that the moving precision is improved until the whole moving process is completed. That is, when the plane moving platform 20 moves along the X axis, the split two-dimensional grating interferometer can also measure the micro displacement of the Y axis in real time, the "unexpected" motion coupling error is generated by the guiding error of the motion system, the motion error is transmitted to the micro-motion platform in real time to perform position correction, and by the closed-loop control, the motion guiding mechanism with conventional precision can realize ultra-high precision motion control, which is helpful for reducing the dependence of the measuring device on the precision of the guiding mechanism; in addition, the closed loop control described above may also provide virtual geometric criteria for metering.
Preferably, the control module is provided with a database and a self-learning algorithm (the algorithm is a conventional algorithm and is not described herein), the expected displacement information, the correction information corresponding to the expected displacement information and the actual displacement information are all recorded into the database, when the same expected displacement is received next time, the control module receives the expected displacement information, then utilizes the self-learning algorithm to call the correction information from the database and sends the correction information to the large displacement driver and/or the micro displacement driver as control information to serve as feedforward error compensation information, namely, the information in the database can be used as motion coupling feedforward compensation information to be sent to the controller, so that the control blindness is reduced, and the control system is helped to enter a steady state relatively quickly.
The grating reading head 40 in this embodiment may be a reading head used in a conventional grating interferometer, as shown in fig. 5 and 6, which are two optical path structures of the grating reading head that can be used in this embodiment, and the half-wave plate 61, the photodetector 62, the rectangular prism 63, the parallelogram prism 64 and the depolarizing beam splitter prism 65 used in these two optical path structures are conventional optical elements, which will not be described in detail herein. In order to influence direct current interference, the grating reading head 40 in this embodiment adopts a high tolerance optical path design and adopts a double-splice interference technology, specifically, as shown in fig. 4, the grating reading head 40 in this embodiment includes a laser transmitter 41, a first light splitting element 42 for receiving dual-frequency laser emitted by the laser transmitter 41, a first coherence module 43 and a polarization splitting element 44 respectively for receiving light beams emitted by the first light splitting element 42, a reflecting mirror 45 for reflecting light beams emitted by the polarization splitting element 44 onto a corresponding grating line group 32, a second coherence module 46 matched with the polarization splitting element 44, and a calculation comparison module 47 respectively connected with the first coherence module 43 and the second coherence module 46, where the laser transmitter 41 is a dual-frequency He-Ne laser, and because of adopting a dual-frequency laser as a light source, the design can effectively avoid measurement errors caused by direct current drift (for this embodiment, when the grating reading head 40 moves relative to the corresponding grating line group 32 along the grating level, the difference can not be eliminated due to the fact that the direct current drift can effectively interfere with each other because of the two-frequency He-Ne laser is a dual-frequency He laser. The first light splitting element 42 and the polarization light splitting element 44 are both light splitting prisms, but the light splitting prism serving as the polarization light splitting element 44 is provided with a plurality of lambda/4 wave plates 48 (lambda is the wavelength of light), and the positions of the reflectors 45 are required to be arranged according to actual needs so as to ensure that the light speed can return along a path after entering the grating line group 32, thus ensuring that the change of the distance between the light path and the grating line group 32 does not influence the occurrence of interference phenomenon, and the light splitting element has good motion tolerance performance and is convenient to install. Furthermore, the calculation comparison module 47 comprises two integration modules connected to the first coherence module 43 and the second coherence module 46, respectively, and a phase comparison module for comparing the two integration modules. The first and second coherence modules 43, 46 and the computation comparison module 47 are conventional modules and will not be described in detail herein.
When in use, the dual-frequency laser beam emitted by the He-Ne laser contains two extremely close frequencies of f1 and f2, the dual-frequency laser beam is divided into two beams by the first light splitting element 42, one beam directly enters the first coherent module to form beat frequency interference, namely static interference, and the beat frequency interference is used as a reference component; the other beam is incident on the polarization splitting element 44, the light with the frequencies f1 and f2 is transmitted and reflected respectively due to the polarization states of the other beam (in this embodiment, the transmission is given by f1, the reflection is given by f 2), the other beam is incident on the grating group 32 in a moving state by means of the different reflectors 45, and the diffracted light returns along the original path respectively, and the frequencies of the two diffracted light become f1+Δf and f2- Δf respectively due to the effect of doppler shift; due to the function of the lambda/4 wave plate 48, after passing through the lambda/4 wave plate 48, the polarization state of the two light beams is changed, the original transmitted light beams are reflected when passing through the polarization beam splitting element 44 for the second time, and the original reflected light beams are transmitted when passing through the polarization beam splitting element 44 for the second time, so that the two light beams do not return to the He-Ne laser, but enter the second correlation module to generate an interference signal with the frequency of f1-f2-2 delta f, and the signal and a reference interference signal with the frequency of f1-f2 are subjected to integral and comparison operation to obtain displacement information of the grating, and the physical principle is that: the Doppler frequency shift delta f is in direct proportion to the speed, and the displacement can be obtained after integral operation; the component f1-f2 can be eliminated through comparison operation, and in the process, the component f1-f2 does not influence the displacement calculation result, but exists as a carrier wave. In the above optical path, the optical paths of the two interference beams are equal and have the same number of reflections with parity, so that when the grating group 32 deflects, the two beams are not separated, thereby ensuring good interference intensity.
The present invention has been described in detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited to the above embodiments, and those skilled in the art can make various modifications to the present invention according to the prior art, which are all within the scope of the present invention.
Claims (3)
1. The measuring device based on the separated grating is characterized by comprising a control module, a base, a plane moving platform horizontally and slidingly connected to the base, a grating rigid body fixedly connected to the plane moving platform, and grating reading heads and measuring heads respectively and fixedly connected to the base, wherein the grating rigid body is provided with a through hole, the measuring heads are positioned in the through hole and are positioned on the same plane with the grating surface of the grating rigid body, the grating rigid body is provided with more than two groups of grating lines, the grating lines comprise a plurality of grating lines which are parallel to each other and are sequentially arranged at equal intervals, the number of the grating reading heads is the same as that of the grating lines, the grating reading heads are arranged in one-to-one correspondence with the grating lines, the projection of connecting lines between the measuring heads and the grating reading heads on the grating surface of the grating rigid body and the grating lines in the grating lines corresponding to the grating reading heads are vertically arranged, and the grating reading heads are respectively connected with the control module in a communication manner;
the plane moving platform is vertically and slidably connected with a lifting table positioned below the grating surface of the grating rigid body, the lifting table is slidably connected with a group of grating line groups, and the grating line groups are vertically and slidably connected with the base;
two groups of grid line groups are arranged on the grating rigid body, and grid lines in the two groups of grid line groups are mutually perpendicular;
the plane moving platform is provided with two pairs of first sensors for detecting the motion coupling error of the lifting platform, and the two first sensors in each pair are symmetrically arranged by taking the central line of the table top of the lifting platform as the center;
the base is provided with a large displacement driver and a micro displacement driver for driving the plane moving platform to move;
the grating reading head comprises a laser emitter, a first light splitting element for receiving double-frequency laser emitted by the laser emitter, a first coherent module and a polarization light splitting element which are respectively used for receiving light beams emitted by the first light splitting element, a reflecting mirror which is used for reflecting the light beams emitted by the polarization light splitting element to the corresponding grating line group, a second coherent module matched with the polarization light splitting element, and a calculation comparison module which is respectively connected with the first coherent module and the second coherent module;
after the expected displacement information is input into the control module, the control module sends control information to the large displacement driver and/or the micro displacement driver according to the expected displacement information, the large displacement driver and/or the micro displacement driver drives the plane moving platform to slide relative to the base according to the control information, meanwhile, the measuring head feeds back actual displacement information of the plane moving platform to the control module, the control module sends correction information to the large displacement driver and/or the micro displacement driver according to the actual displacement information, and the large displacement driver and/or the micro displacement driver continuously drives the plane moving platform to slide relative to the base according to the correction information.
2. The split grating-based measurement apparatus of claim 1, wherein the large displacement driver is a stepper motor and the micro displacement driver is a piezo-ceramic driver.
3. The split grating-based measurement apparatus of claim 1, wherein the control module has a database, the desired displacement information and the correction information corresponding to the desired displacement information are entered into the database, and the control module retrieves the correction information from the database after receiving the desired displacement information and sends the correction information as control information to the large displacement driver and/or the micro displacement driver as feedforward error compensation information.
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| Publication number | Priority date | Publication date | Assignee | Title |
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