DE102004010083B4 - Probe of the measuring type for a coordinate measuring machine - Google Patents

Abstract

probe of the measuring type for a coordinate measuring machine with a fixed part (4 ') and at least one in the vertical direction on the other hand displaceable part (4 ''), wherein the displaceable part (4 '') with a position measuring device (11), a mechanical interface (8) to accommodate probe configurations of different weights and a motor-operated device (12 to 17) for mechanical Compensation by the different key combination weights caused different resting states of at least one vertically movable part (4 '') relative to the fixed part (4 ') and equipped with a control device, the motorized device for mechanical compensation different probe combination weights to compensate for the different Quiescent so regulates that regardless of the key combination weight always the same, by the zero point of the position measuring system of the at least one vertically movable part defined rest position is achieved, wherein the control device is a non-linear regulator structure characterized in that state variables of the Probe of the measuring type one phase space of the system with one Form switching trajectory and that the switching trajectory accordingly a vibrational state of the probe changeable ...

Description

The The invention relates to a probe of the measuring type for a coordinate measuring machine according to the preamble of claim 1.

In Coordinate metrology probes are known, which are essentially be described in two categories that characterize the procedure, with the touch (Probing) of the probe, usually a stylus with probing ball is detected on the workpiece.

Probes from switching type detect the probing, for example, by evaluating a structure-borne sound impulse, the one at the touch with the workpiece arises or by opening or close of a circuit, if by the probing forces a kinematic bearing is brought from its rest position. These switching probes are connected to a device that allows it in three spatial directions free to move with the aim of having the probing ball at any one Place with the workpiece to bring into contact. These probes have the advantage that they are mechanically simple and therefore inexpensive to implement. They have however the disadvantage that with them a continuous scanning (Scanning) of the workpiece not possible is.

For this needed man probes of the measuring type. They consist of a solid part that with a Device connected to the probe in three room dimensions move and position freely within a defined measuring volume can, as well as three commonly orthogonal, opposite the fixed part of moving parts. The moving parts are often as Swings formed with parallel spring plate guide, the one exact guidance in each case allows a spatial direction. The three swings build kinematically on each other so that the last swing of the kinematic chain within a range of motion in shape a cube of typically a few millimeters edge length is freely movable. Further are reset elements provided that bring the probe rockers in a rest position, which is located approximately in the middle of the range of motion, if no external forces the swings are working. Furthermore, position measuring devices are provided, which measure the deviation from the rest position of the individual swings and thus define a deflection vector of the kinematically last swing. The zero points of these position measuring devices usually define the quiescent position.

At the last swing is usually one mechanical interface provided, which allows automatic switching allows so-called button combinations. This interface consists of a kinematically defined storage, which is exactly all Defines six kinematic degrees of freedom, thus repeated Replacing the same probe combination the relative position between the probe rocker and this combination of probes possible is exactly reproduced.

At the Change of different heavy duty button combinations will the probe rocket that defines the vertical axis through the different weight of different probe combinations different steered ahead and is in the free state in one Position that does not coincide with the zero point of the position measuring device. Because this is undesirable is, the measuring probes are common equipped with a taring device (weight compensation), the vertical swing so brings to its rest position that the position measuring device is at zero point and she still can move freely.

To the State of the art (WO 02/073123 A1) includes a probe with a respect to the fixed part of the probe in at least one direction of measurement movable Stylus and an associated buoyancy, which is the movable, the stylus carrying part in at least one measuring direction in can tare a desired position.

This belonging to the prior art probe with control device has the disadvantage that Tasterwechselzeiten are very long due to vibrations occurring.

The prior art ( DE 38 42 151 A1 ) belongs a probe of the switching type. The control of this probe performs after each change of the stylus by a taring, in which by a corresponding increase in pressure or pressure reduction in the printing cylinder, the weight difference between different styluses is compensated in such a way that the force with which the movable part of the probe is in his camp , remains constant. An adjustment of a rest position, as in a measuring probe, is not provided here.

These prior art control relates to a probe of the switching type. The term "taring" is used according to this Document understood that the pressure force of bearings and Counter bearing is kept constant.

The prior art ( DE 37 25 207 A1 ) includes a probe for coordinate measuring machines, in which for each of the three spatial axes an associated spring system a Tariereinrichtung switched on is that automatically adjusts the zero position of the spring system in each spatial position of the probe.

This belonging to the prior art probe again has the disadvantage that Tasterwechselzeiten due to occurring Vibrations are very long.

The The technical problem underlying the invention is that the key change times in a coordinate measuring machine with a Probe of the measuring type to shorten, especially high weights to position very quickly in the Z-axis at a low Vibration excitation and a very fast deceleration in the target point to reach.

This technical problem is due to a probe with the characteristics of Claim 1 solved.

Thereby, that the control device is designed as a non-linear regulator, the key change times are considerably shortened. The necessary control technology Effort in terms of security of compliance with stability criteria and thus costs for service calls if the stability criteria are not met due to intentional or unwanted system changes can be kept low in contrast to a complex linear solution Under the conditions of an ever-increasing range of probe weights with simultaneous demand for low probing forces.

The Position control of the measuring head deflection is based on nonlinear control, for example, according to Lyapunov criteria, harmonic Balance or a speed-optimized control.

To initialization and the formation of gauge head state quantities a maximum Meßkopfauslenkschwelle monitored, the possible is small (near the target point of positioning), but at the same time so big that according to the natural frequency of the measuring head and thus the Cooldown of head vibrations of the probe as possible to Rest comes when the destination is reached. Above the threshold the Meßkopfstellelement is advantageous at a constant high speed moved below variable speed.

The Manipulated variable for the motor operated device for mechanical compensation of different Button combination weights advantageously forms a modulator, which is controlled by a position controller and the speed between a positive maximum and a negative minimum and zero switches. The advantage is that the control is very simple and inexpensive, and the friction of the motorized device to the mechanical Compensation of different probe combination weights is not important plays. The switching frequency is selected so high that the sensor head vibrations not additionally stimulated but at the same time so low that the operated equipment independently from their mechanical inertia reacts quickly. The modulator characteristic is non-linear, so that the enema into the target point of positioning as possible low-vibration and still fast.

The Position control of the measuring head deflection is based on non-linear control using a nonlinear switching trajectory. In conjunction with a nonlinear modulator characteristic, the Switching trajectory also be linear.

The State variables of the Measuring head form the phase space of the system with the switching trajectory. They are along with optimum design of the switching trajectory this led up to a defined target area in phase space with as few as possible Switching with ideally non-oscillating measuring head. simultaneously However, the real existing vibrations of the measuring head are monitored. According to the state of vibration becomes the switching trajectory appropriately changed, For example, in the simplest case, only shifted to additional Force switching that counteracts the Meßkopfschwingungen. Al ternativ to the additional Switches can also be at least one state variable of the system suitably the modulator characteristic (pulse width modulation) or the manipulated variable for the motor operated device for mechanical compensation of different Superimposed probe combination weights (amplitude modulation) become.

is The target area in phase space will be reached with the help of changing Switching trajectory possibly still existing residual vibrations on a retriggerable time interval resulting from the measuring head natural frequency derives, reduces, or becomes the algorithm described above completely shut off.

Becomes the weight balance started in the target area of the phase space, the algorithm described above is not activated.

If the weight compensation is started above the monitored maximum Meßkopfauslenkschwelle and vibrates the measuring head due to a shock excitation, for example, triggered in a Tasterwechselvorgang, so that at the non-changing switching trajectory a fixed An number of switches takes place, the above-described algorithm is suspended until a fixed constant time interval has elapsed, in which no switching has taken place. In determining the number of switches and the time interval, the Meßkopfeigenfrequenz and the course of the switching trajectory is used.

With the control device according to the invention Is it possible, a weight difference of, for example, one kilogram in less than three seconds, with a window around the target position is achieved of less than two microns.

Further Features and advantages of the invention will become apparent from the accompanying drawings, in the one embodiment a probe of the measuring type only exemplified is. In the drawing show:

1 a probe of the measuring type in perspective view;

2 a schematic view of the modules of the weight compensation control loop;

3 a possible course of the state variable Z1 of the measuring head;

4 a representation of the influence of a two-point characteristic by the modulator;

5 a non-linear characteristic for driving the modulator;

6 the phase space of the system with a possible switching trajectory;

7 a representation of the operation of the switching trajectory in the phase space of the system;

8th a phase space of the system with a variable switching trajectory;

9 Alternatives to 8th ,

1 shows a measuring probe ( 1 ) as known in the art. The probe ( 1 ) has three probe rocking ( 2 . 3 . 4 ) on. The probe rock ( 2 . 3 . 4 ) allow a deflection of the probe in the X-, Y- and Z-direction. For this purpose, the probe rockers each have a fixed ( 2 ' . 3 ' . 4 ' ) and a relatively movable part ( 2 '' . 3 '' . 4 '' ) on. The fixed parts ( 2 ' . 3 ' . 4 ' ) and the moving parts ( 2 '' . 3 '' . 4 '' ) are over spring plates ( 5 . 6 . 7 ) are each connected to each other displaceable relative to each other.

At a button recording ( 8th ) a stylus (not shown) is attached. Each probe rocker has a position measuring system ( 9 . 10 . 11 ) on. The probe ( 1 ) has counterbalance springs ( 12 . 13 . 14 ), which with a spindle nut ( 15 ) are connected. A spindle ( 16 ) is used to move the spindle nut from a motor ( 17 ).

2 shows individual modules M1 to M5 of the weight compensation control loop ( 20 ). In M1, the sensor status values are determined online and made available for further processing of the following components. In M2, the mathematical calculation of the switching trajectory and its change takes place online. Here it is determined whether the state variables are below or above the switching trajectory. This is the actual position controller. The module M3 represents the modulator. This influences, taking into account the input values U1 and U2, a two-point characteristic, such that a suitable control U3 of the motor-operated device for mechanical compensation of different probe combination weights. The module M4 is the motor-operated device for mechanical compensation of different probe combination weights, described by the linear or non-linear transmission element L1. The motor-driven device for mechanical compensation of different probe combination weights works electromechanically or pneumatically. The entire controlled system "measuring head" is shown as transmission element L2 in M5.

3 shows a possible course of the state variable Z1 over the time t. The state variable Z1 indicates the position and the state variable Z2 the speed. The ideal course V is superimposed on a real oscillation which should have subsided to a large extent when the target area Z _{ZG1 is reached} at Z _ZG . The course ends at the time t _end as close as possible to the destination Z _ZP . The state variable Z2, which forces this course, is kept constant above a maximum deflection threshold Z _M , below which is suitably variable.

4 shows the influence of the two-point characteristic by the modulator M3 over the time t. Apart from the setting of a positive maximum "max" at the switching time t _U , the manipulated variable U3 is switched to "zero" at suitable times t _N, or back to "max" at t _M. The same applies to the setting of a negative minimum "min".

5 shows a non-linear characteristic for controlling the modulator M3 via the input U2 in dependence of the state variable Z1 with exem Plausible represented manipulated variables U3. Above Z _M , the positive maximum "max" is permanently set (U3 ₁ at point P1 of the characteristic curve). Below Z _M is switched between "max" and "zero" according to the representation U3 ₂ and U3 ₃ in the points P2 and P3 of the characteristic. The same applies to the case in which Z _{M is} smaller Z _ZP by _mirroring the characteristic curve on an axis through Z _ZP parallel to the U2 axis.

6 shows the phase space of the system with a possible switching trajectory ST. Starting from a start deflection Z _{SA of} the measuring head, its state variables Z1 and Z2 change in such a way that the trajectory of the system TS ideally approaches the target region ZG along the switching trajectory. It will take place as few switching UP. The target area ZG itself is formed from the intersection of the two target areas Z _ZG1 and Z _ZG2 for the individual state variables Z1 and Z2.

7 shows in the phase space of the system, the operation of the switching trajectory ST. Starting from a start deflection Z _{SA of} the measuring head, switching takes place in the points UP1 and UP2 with a switching trajectory ST. Without a switching trajectory ST, the switching takes place at points UP3 and UP4. In the first case, the trajectory of the system TS1 approaches the minimum of the state variables Z1 and Z2 much faster than in the second case the trajectory TS2. The appropriate choice of the switching trajectory ST leads to a speed-optimal control.

8th shows the phase space of the system with a variable trajectory ST. Starting from a start deflection Z _{SA of} the measuring head, the time of switching UP _{B can be} advanced to UP _A or delayed to UP _C. The trajectory ST is changed according to the phase position of the Meßkopfschwingungen so that the vibrations decay as quickly as possible.

9 shows alternatives 7 , Probe vibrations are minimized by suitably changing the manipulated variable U3 in its amplitude AM or in the pulse width PM.

1

probe

2, 3, 4

scanning head rocker

2 ', 3', 4 '

solid Part of the probe swing

2 '', 3 '', 4 ''

Portable Part of the probe swing

5, 6, 7

spring plates

8th

Probe body

9 10, 11

measuring systems

12 13, 14

Counterbalancing springs

15

spindle nut

16

spindle

17

engine

20

Counterbalance loop

Claims (10)

Probe of the measuring type for a coordinate measuring machine with a fixed part ( 4 ' ) and at least one vertically displaceable part ( 4 '' ), whereby the displaceable part ( 4 '' ) with a position measuring device ( 11 ), a mechanical interface ( 8th ) for receiving probe configurations of different weights and a motorized device ( 12 to 17 ) for the mechanical compensation of the different rest positions of the at least one vertically movable part caused by the different combinations of key combination ( 4 '' ) relative to the fixed part ( 4 ' ) and a control device which controls the motor-operated device for mechanical compensation of different combination key weights to compensate for the different rest positions so that regardless of the key combination weight always the same, defined by the zero point of the position measuring system of at least one vertically movable part rest position is achieved, the Control device has a non-linear regulator structure, characterized in that state variables of the probe of the measuring type form a phase space of the system with a switching trajectory and that the switching trajectory is variable according to a vibration state of the probe. Probe according to claim 1, characterized in that that the control device as one based on the nonlinear Regulation according to criteria of Lyapunov or according to the procedure of harmonic balance working re geleinrichtung or as speed-optimized Control device is formed. Probe according to claim 1, characterized in that that the control device is a switching regulator with a switching trajectory in the speed / position phase space. Probe according to claim 1, characterized in that the motor-operated device for mechanical compensation of different probe combination weights is designed as a device controlled by a pulse width modulator, wherein the pulse width modulator as a merely between the states "positive maximum speed", "negative maximum speed" and "zero speed" switching pulse width modulator is formed. Probe according to claim 4, characterized in that that the pulse width modulator with respect to a non-linear characteristic on the speed or the position. Probe according to one of claims 1 to 5, characterized that for damping of vibrations during the control process, the position of the switching trajectory in the phase space variable is. Probe according to one of claims 1 to 6, characterized that damping occurring oscillations by amplitude or pulse width modulation the drive signals of the motor-operated device for mechanical rule Compensation of different probe combination weights is done. Probe according to one of claims 1 to 7, characterized that the control device is switched off when the stylus carrying part in a predetermined target area of finite extent located in the phase space. Probe according to one of claims 1 to 8, characterized that the at least one motor-operated device for mechanical compensation different probe combination weights than one with continuous Maximum speed traveling device is formed, as long as the deflection of the stylus bearing part a predetermined Value exceeds. Probe according to Claim 1, characterized in that a first state variable (Z1) indicates the position and a second state variable (Z2) the velocity, and that the second state variable (Z2) is constant above a maximum deflection threshold (Z _M ) and below the maximum deflection threshold (Z _M ) is kept variable in a suitable manner.