WO1997008595A1

WO1997008595A1 - Device for compensating guide tolerance in multi-axis positioners

Info

Publication number: WO1997008595A1
Application number: PCT/DE1996/001149
Authority: WO
Inventors: Hans-Jürgen HESSE
Original assignee: Hesse Gmbh
Priority date: 1995-08-29
Filing date: 1996-06-28
Publication date: 1997-03-06
Also published as: AU6352696A; EP0847548A1; DE19531676C1

Abstract

A device for compensating guide tolerance in multi-axis positioners in which a second guide substrate (FY) can be moved or pivoted on a first guide substrate (FX) in relation to a first axis (X) and a further guide substrate or an object (O) can move or pivot via an appropriate positioning drive (MY) on the second guide substrate (FY) in relation to a second axis (Y) and the movement on the guide substrates (FX, FY) is continuously detected by an appropriate coordinate measuring device (APX, APY), where at least one measuring emitter (S1-S4) with a narrow aperture is fitted on the guide substrates (FX, FY) oriented parallel to the guide, and on the guided component (FY, O) on which the individual measuring beams impinge is arranged a deviation measuring device (AMX, AMY, AMZ1, AMZ2) in such a way that its deviation measurement signal (SMX, SMY, SMZ1, SMZ2) indicates at least one position deviation transversely to the direction of the impinging measuring beam.

Description

Device for compensating guide tolerances in multi-axis positioners

The invention relates to a device for guiding tolerance compensation on multi-axis positioners, a second guiding bracket being displaceably or pivotably mounted on a first guiding bracket with respect to a first axis by means of an associated positioning drive, and a further guiding bracket or on the second guide bracket with respect to a second axis an object is mounted displaceably or pivotably by an associated positioning drive and the respective displacement on the guide supports is continuously determined by an associated coordinate measuring device.

It is known in multi-axis positioning systems, e.g. X- / Y-tables, portals, measuring machines, positioning devices in which a highly precise approach to a position is required, the achievable accuracy of the positioning depending on the tolerances of the axis guides. Tolerances occur both in the vertical and in the horizontal direction of the guides, i.e. each transverse to the positioning direction. Extreme accuracy requirements for guides, such as those placed on measuring machines, for example, increase the system price considerably, and such guides are unsuitable for use in processing machines, for example, because the load capacities are too low.

If an object, for example a measuring pin or tool, is positioned in two axes with respect to a stationary base, the object-side positioning device, for example a so-called cross support, is carried and moved by the base-side positioning device. The latter works in its direction of positioning, ie towards the cross support, just as precisely as its direct or indirect, ie spindle-related, scale and the associated measuring device are designed. In the second The object-side positioning device works in the same direction in relation to the movable object as the associated scale and the measuring system cooperates with it. However, the position of the object in the two directions, based on a fixed basis, differs from the specifications of the two measuring systems, which are each transverse to the positioning directions in the associated guides. The same problem occurs twice with three-axis positioning, since the respective position measurement value indicates the position between the object and the base, each with guide deviations lying in two different guides.

Such a multi-axis positioning device has become known from DE 43 12 255 AI. This publication describes an x, y coordinate table in which a y guide plate is arranged on a y base plate with the interposition of actuators and on which there is an x base plate which can be moved in the y direction. The movement of the x-base plate is realized by a nut-spindle gear, whereby a y-guide rod with an associated y-guide bearing is additionally provided. On the x-base plate there is also an x-guide plate, on which a table element is mounted displaceably in the x direction via a further nut-spindle gear. Since the threaded spindle and the guide rods cannot be machined to an exact concentricity, any adjustment of the coordinate table in the x or y direction leads to a slight change in position in the z direction. These changes in position are corrected with the aid of measuring devices which actuate the actuators, so that they can carry out an opposite change in position to compensate for the changes in z-position. Such a coordinate table is therefore technically very complex to implement.

It is an object of the invention to provide a base-related, substantially more precise multi-axis positioning of an object with simple means, even with static or load-related deformation of the guide. The solution is that at least one measuring radiator with a narrow aperture is arranged parallel to the guide on each of the guide carriers and a deviation measuring device is arranged on each of the guided parts of the individual measuring beams so that their deviation measuring signal each transverses at least one position deviation signaled to the direction of the incident measuring beam.

Advantageous configurations are given in the subclaims.

For the measurement of the respective guide deviations, narrowly focused beams, e.g. Laser beams, once sent from the base on the guide support to the cross support and the second from the latter to the object table and recorded there and there with receivers measuring the tolerance ranges of the respective guides, the measured values of which are output in each case the transverse deviation state the position of the guided part in at least one of the other axial directions.

The base-related object position for the individual axis directions thus results in each case as a sum of the position measurement value in the relevant axis and the position deviation measurement value (s) lying in the same direction and measured by the further position device (s) .

In the case of a measuring system in which positioning is carried out on a base-mounted measurement object, for example with a sensor, the sums mentioned can be used directly as precise, base-related coordinate measurement values.

For a base-related positioning of an object with position controllers, the respective sums relating to the corresponding coordinate direction are supplied to the associated position controllers as actual coordinate values.

Leave the deviations in the position of the positionable object are measured for axes along which the part to be positioned is guided, as well as for rotary or swivel axes and used to supplement the rectified position measurement values. When measuring the positional deviations of parts to be positioned in rotation, the measuring beam is preferably sent coaxially to the axis of rotation, for example through a hollow axis, and directed onto a two-dimensionally operating offset measuring device on the part which is mounted in a rotatable manner. In principle, the assignment of the light transmitter, for example the laser, and the measuring receiver to the two mutually positionable parts is arbitrary, but the pivoting of the guided part that occurs in the guide has a much smaller effect on the accuracy of the measurements of the deviation when the receiver on the ge ¬ led part is arranged.

An arrangement with a beam and with a two-dimensional receiver, e.g. a two-dimensional CCD array. The center of the beam can be determined from the image data of the beam thus obtained and its coordinates can be obtained as the two dimensions of the deviations. The coordinates are expediently measured with reference to those initial coordinates which are recorded in a basic positioning position used for calibration. Of course, pure relative position measurements and relative positioning can also be carried out without prior calibration to a specific starting position.

Instead of a two-dimensional measuring array, linear arrays of photosensitive cells can also be used, whereby optical means and / or suitable evaluation must ensure that deviations in only one direction affect the measurement in this direction of deviation and the deviation in the other direction does not cause the beam to leave the linear array feed area.

In general, it can be assumed that the length of a conventional CCD array with, for example, 256 or 512 positions is greater than the length of the deviation range to be recorded. For this reason, the beam path is expanded in this direction towards the end positions in such a way that there is roughly a match between the two lengths. For this purpose, a cylindrical scattering optics or also a collecting optics can be used if the array is arranged behind the focal point.

The simplest way to adapt the deviation range to the length of the linear array is to arrange the array at an angle.

Furthermore, when vertical, i.e. transversely, to the array there is a larger deviation range than the array width, a collection of the beam paths in this area is made focusing on the array by placing a correspondingly cylindrical converging lens in this direction or a cylindrical concave mirror in the beam path. In general, one will cross a collecting and a scattering optical element, so that extensive use of the beam always occurs in the entire array area. The array output signals are each evaluated by determining a center of gravity with respect to the beam component that is incident in each case, that is to say on its central position.

When using the method it is a prerequisite for achieving usable deviation measurement values that the beam is always in a defined position in space. This means that the radiation source must advantageously be arranged on the guide or so that the measuring beam is always parallel to this. However, if the radiation source is attached particularly simply to the end of the guide or the guide support and if the latter are subject to a noticeably changing deflection when the load changes, then accordingly a different inclination of the support ends and thus the radiation source mounted there also usually occurs. A resulting beam inclination to the guideway leads to a change in the deviation measurement depending on the distance from the radiation source to the Sensor array. This change can advantageously be determined and corrected by pointing a part of the beam or a parallel beam over the preferably entire length of the guide track to an inclination measuring array. With its inclination measurement signal, an inclination correction value is formed in relation to the travel distance to the length of the inclination measurement beam, which value must be added to the position deviation measurement value in order to relate the position of the positioned part to an original basis even in the case of a load-dependent change in beam inclination.

Such inclination changes will usually occur in the load direction, that is to say in particular in the vertical direction, and therefore i.a. the inclination sensor should also be provided there. A beam split by a beam splitter can be passed on partly to the deviation sensor and partly to the inclination sensor. For the inclination measurement, the sensor preferably consists of a linear array with a beam spread by suitable inclination of the sensor. Since i.a. in the event of a load a change in inclination occurs only in one direction, the Z direction, the measuring beam need not be focused in the transverse direction.

Advantageous configurations are shown in FIGS. 1 to 3.

Fig. 1 shows a section of a two-axis positioning device;

2 shows an enlarged sensor arrangement;

Fig. 3 shows a tilt measuring device schematically.

FIG. 1 shows a two-axis positioning device in an XY plane with two deviation measuring devices AMX, AMZ1 per positioning device; AMY, AMZ2, each with a laser beam light source S1-S4 and with one positioning device, one axis position measuring device APX, APY, which consists of a measuring ruler LX, LY and an associated coordinate sensor exist. The two coordinate drives consist of motors MX, MY, which are controlled by a position control device ST. Setpoint values Xsoll, Ysoll are fed to this positioning device, which are continuously compared with the actual position values Xist, Yist for a controlled position control, so that the differences between the setpoint and actual values are used as the controller control variable of the motors MX, MY serve.

The actual position signal of the X positioning Xactual results from the sum of the X coordinate measurement value SPX and the deviation measurement signal SMX lying in the X direction; The same applies to the actual position signal Yact in the Y direction. The corresponding reference characters contain the letter Y.

The two deviation values SMZ1, SMZ2 in the Z direction are also summed and used as a Z coordinate deviation DZ. Depending on the application, these can be omitted. If there is also a Z positioning device, this is provided with further X or Y coordinate deviation measuring devices, and their measured values are also added to the rectified sums.

The various deviation measuring devices AMX, AMZ1; AMY, AMZ2 are designed as linear CCD arrays and connected to the control device ST via a multiplexer MPX, so that the signal sequences from the arrays are read out and evaluated one after the other and then fed to the sum formation. The switching elements shown are preferably implemented by a program in the control device ST equipped with a microprocessor.

The two linear sensor arrays of each axis positioner can also be replaced by a two-dimensional array. Then only a single measuring source S1, S3 is required for this. The measuring radiators S1, S2; S3, S4 are each mounted on the head on the guides FX, FY and the deviation measuring device AMX, AMZ1; AMY, AMZ2 are each arranged on the slides mounted thereon, the cross slide K or the object slide 0.

FIG. 2 shows a first sensor arrangement with a measuring emitter S1, the laser beam of which strikes the deviation measuring device AMY, which is mounted on the cross slide K, parallel to the X axis and to the guide FX. In order to adapt the maximum tolerance range T of the deviation to be measured to the length L of the linear sensor array LSA, beam scattering is provided via a cylindrical arched mirror WS.

A concave curvature can be superimposed on the convex cylinder rotated by 90 °, so that in the event of positional deviations perpendicular to the image plane, the measuring beam always falls on the linear array LSA and does not migrate laterally beyond it. In the present example, the sensor array LSA is preceded by a cylinder lens ZL whose cylinder axis is parallel to the array LSA and whose focal line lies on it.

FIG. 3 shows an arrangement of a long guide support FX with a cross slide K. The measuring source S1 is mounted at the end of the support FX and on the slide K the deviation sensor AMZ1, which in particular determines the load deflection of the support FX. Since the ends of the carrier F incline towards an unloaded starting position during load deflection, the beam path S1 'also inclines to the same extent, whereby the deviation sensor AMZ1 measures the deviation with respect to the inclined measuring beam S1 and not to the output beam path. A parallel beam S1 "is therefore advantageously guided to an inclination sensor NZ at the other end of the carrier FX. Its inclination measurement value SNZ is proportional to the length LS 'of the first measurement section of the first measurement beam S1", which is known as the X-displacement measurement signal SPX, and fed in reverse proportion to the length LS "of the second measuring beam S1" to the Z coordinate summer, as are the Z deviation values SMZ1, SMZ2 and possibly a Z coordinate measurement value SPZ, so that a Z actual value Ziεt is available as the summation result and can be used in the control device ST with a Z coordinate setpoint Zsetpoint to control the controlled actuation of a Z positioning motor.

The same principle of correcting the inclination of the deviation measurement can of course also be used in the case of expected inclinations or inclinations of the other guides.

Claims

claims

1. Device for compensating for guide tolerances on multi-axis positioners, a second guide carrier (FY) being mounted displaceably or pivotably on a first guide carrier (FX) with respect to a first axis (X) by an associated positioning drive (MX) and on the second guide carrier (FY) with respect to a second axis (Y) a further guide support or an object (0) is mounted displaceably or pivotably by an associated positioning drive (MY) and the respective displacement on the guide supports (FX, FY) by an associated coordinate measuring device (APX, APY) is continuously determined, characterized in that at least one measuring radiator (S1 - S4) with a narrow aperture is arranged on the guide carriers (FX, FY), aligned parallel to the guide, and on the respective guided part (FY, 0 ) each of the individual measuring beams is acted upon by a deviation measuring device g (AMX, AMY, AMZ1, AMZ2) is arranged in such a way that their deviation measurement signal (SMX, SMY, SMZ1, SMZ2) signals at least one positional deviation transversely to the direction of the incident measuring beam.

2. Device according to claim 1, so that the measuring emitters (S1-S4) are laser emitters.

3. Device according to claim 1, characterized in that the deviation measuring device (AMX, AMZ2; AMY, AMZ1) are two-dimensional CCD arrays, each of which receives a measuring beam center from the received signals. is averaged, whose coordinates in the array serve as two of the deviation measurement signals (SMX, SMZ2; SMY, SMZ1).

4. Apparatus according to claim 1 or 2, so that the deviation measurement devices (AMX, AMY, AMZl, AMZ2) each consist of a linear CCD array.

5. Apparatus according to claim 4, d a d u r c h g e k e n n - z e i c h n e t that the tolerance range to be measured

(T) the deviation is adapted by a cylindrical optical means (WS) of length (L) from the downstream CCD array (AMX, AMY, AMZl, AMZ2).

6. Apparatus according to claim 4 or 5, dadurchge ¬ indicates that the CCD array (AMX, AMY, AMZl, AMZ2) is preceded by an optical means (ZL) which the measuring beam (Sl- S4) in the event of positional deviations transverse to the stretching direction of the CCD array focused on this.

7. Device according to one of the preceding claims, since ¬ characterized in that parallel to or coaxially branched from at least one of the measuring beams (SL ') a second measuring beam (Sl ") is directed to an inclination measuring device (NZ) which the same guide support (FX) as the measuring radiator (Sl) is arranged and the inclination measurement signal (SNZ) from the inclination measuring device (NZ) is proportional to the respective beam length (LS of the first measuring beam (Sl ') and vice versa proportional to Length (LS ") of the second measuring beam (S") summed to the deviation measuring signal (SMZ1) of the deviation measuring device (AMZl) of the first measuring beam (S1 ') lying in the same direction.

8. The device according to claim 7, characterized in that the inclination measuring device (NZ) contains a linear CCD array.

9. Device according to one of the preceding claims, since ¬ characterized in that at least one of its positioning drives (MZ) is controlled via a control device (ST) which measures the sum of the associated coordinate measurement value (SPZ) and the rectified deviation measurement values (SMZ1, SMZ2) and possibly the relativized inclination measurement signals (SNZ) as the actual position value (Ziεt) and a set position value (Zsoll).

10. Device according to one of the preceding claims, since ¬ characterized in that the output signals of the CCD arrays (SMX, SMY, SMZl, SMZ2) are multiplexed a microprocessor control / regulating device (ST) are supplied, which these signals with respect evaluates a beam center position and determines the coordinate deviation value from the respective center position and sums it up with the rectified measured values (SPX, SPY, SPZ).