JP6820100B2 - Control method of shape measuring device - Google Patents

Description

The present invention relates to a control method for a shape measuring device.

A shape measuring device that detects the surface of an object to be measured by a probe is widely used. The probe is attached to the coordinate measuring machine so that it can move three-dimensionally. Further, there is a probe itself having a built-in rotation shaft as a movable probe head.
(Hereinafter, in this specification, the movable probe head is simply referred to as a probe head.)

An example of the probe head 500 is shown in FIG. 1 (Patent Document 1: Patent No. 2873404).
As shown in FIG. 1, the probe head 500 has a head fixing portion 501 and a stylus 502 having a measuring tip 503 at its tip.
The probe head 500 is attached to the coordinate measuring machine by the head fixing portion 501.
Two rotation mechanisms 510 and 520 are provided between the head fixing portion 501 and the stylus 502. The two rotation mechanisms include a first rotation mechanism unit 510 having the first rotation axis A1 as the rotation axis and a second rotation mechanism unit having the second rotation axis A2 orthogonal to the first rotation axis A1 as the rotation axis. 520 and are provided.

Therefore, the measuring chip 503 drives a total of five drives, that is, the three drive axes (X-axis, Y-axis, and Z-axis) of the coordinate measuring machine and the two rotation axes A1 and A2 built in the probe head 500. It can be moved by the axis.
Since the shape measuring device can control the position of the measuring tip 503 with five axes instead of just three axes, it is possible to measure a workpiece having a complicated shape at high speed.

Patent No. 2873404

Since the measuring tip 503 can be moved by five drive shafts, it has become possible to measure a complicated workpiece at high speed, but a new problem has arisen.
For example, when moving the measurement chip 503 to the next measurement target location, consider moving the measurement chip 503 from the first point to the second point (see, for example, FIG. 4).
The shape measuring device can move the measuring chip 503 to the position (x, y, z, α, β) of the second point, which is the target point, to that position.
Here, α represents the rotation angle (first rotation angle) of the first rotation mechanism unit 510, and β represents the rotation angle (second rotation angle) of the second rotation mechanism unit 520. That is, the movement of the measurement chip 503 means that not only the three-dimensional position (X, Y, Z) changes but also the posture (α, β) of the probe head 500 changes.

Where there are drive axes (X-axis, Y-axis, Z-axis) of the three-dimensional measuring machine 200 and drive axes of the probe head 500 (first rotation axis A1, second rotation axis A2), each drive axis is a drive axis. Optimal drive control is achieved by positioning feedback control for each.
Then, the target point (second point) is reached.
However, although the target point (second point) can be reached, it is unclear how the measuring chip 503 moves along the route on the way, and it is not known until the measurement chip 503 moves.

If the measuring tip 503 swings more than the operator expected during the movement, the measuring tip 503 (or stylus 502) and the work may interfere with each other. Then, the measuring tip 503 (or the stylus 502) and the work are damaged.
As an operator, it is necessary to be careful not to interfere with the stylus 502 and the work when the probe head 500 is moved, but since the trajectory of the measuring tip 503 cannot be easily predicted, there is a large margin or what. There is no choice but to try it several times and check carefully.

An object of the present invention is to provide a control method for a shape measuring device capable of predicting a movement path of a measuring chip in a shape measuring device capable of controlling five axes.

The control method of the shape measuring device of the present invention is
A stylus having a measuring chip at the tip, a first drive shaft that is rotationally driven around the first rotary shaft, and a second drive shaft that is rotationally driven around a second rotary shaft that is orthogonal to the first rotary shaft. A probe head that has and changes the posture of the stylus by the rotational movement of the first drive shaft and the second drive shaft.
A three-dimensional measuring machine having a third drive shaft, a fourth drive shaft, and a fifth drive shaft as three translational axes orthogonal to each other and three-dimensionally displacing the position of the probe head is provided.
The position of the measuring chip is given by the coordinate values (T3, T4, T5) of the third to fifth drive shafts, and the posture of the probe head is the first rotation angle α of the first drive shaft and the said. It is a control method of the shape measuring device given by the second rotation angle β of the second drive shaft.
The movement route starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) to the target position He (Te3, Te4, Te5, αe, βe) is set by the operator.
In the movement path from the current position Hs (Ts3, Ts4, Ts5, αs, βs) to the target position He (Te3, Te4, Te5, αe, βe), the interpolation points for each control cycle are set from the first to the first. Obtained for each of the 5 drive shafts
When the intersection of the first rotation axis and the second rotation axis is the rotation center Q, the above-mentioned is described by a predetermined conversion formula in which the values of the interpolation points (αi, βi) of the first and second drive axes are taken into consideration. The coordinate value of the intersection point of the measurement chip is converted into the coordinate value of the rotation center Q to obtain the control interpolation point Qi.
For each control cycle, the third to fifth drive shafts are positioned and controlled at the control interpolation point Qi, and the first and second drive shafts are the interpolation points (αi,) of the first and second drive shafts. It is characterized in that positioning control is performed on βi).

In the present invention
The movement path starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) is set as a linear movement path. It is preferable to have.

In the present invention
The movement path starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) to the target position He (Te3, Te4, Te5, αe, βe) is set as a bent linear movement path. It is preferable that it is.

In the present invention
The movement path starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) is set as an arc-shaped movement path. It is preferable to have.

In the present invention
Velocity patterns starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) are generated for each of the first to fifth drive shafts.
For the speed patterns generated for the third to fifth drive shafts, a common speed pattern is set for each of the third to fifth drive shafts so as to synchronize with a common acceleration / deceleration time and a common required time. It is preferable to generate.

In the present invention
Velocity patterns starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) are generated for each of the first to fifth drive shafts.
A common speed pattern is generated for each of the first to fifth drive shafts so that the speed patterns generated for each of the first to fifth drive shafts are synchronized with a common acceleration / deceleration time and a common required time. Is preferable.

It is a figure which illustrates the probe head. It is a figure which shows the whole structure of a shape measurement system. It is a figure which shows the sectional view of the probe head. It is a figure which illustrates the movement of a probe head. It is a flowchart for demonstrating the control method of a shape measuring apparatus. It is a figure which illustrates the displacement from the present position Tws (Twsx, Twsy, Twsz) to the target position Twe (Twex, Twee, Twez). It is a flowchart for demonstrating the procedure for generating the speed pattern of each drive shaft. It is a figure which illustrates the speed pattern of the X drive shaft. It is a figure which illustrates the speed pattern of the Y drive shaft. It is a figure which illustrates the speed pattern of the Z drive shaft. It is a figure which illustrates the speed pattern of the 1st rotation mechanism part. It is a figure which illustrates the speed pattern of the 2nd rotation mechanism part. It is a schematic diagram which shows the state of extracting the common parameter from the speed pattern of the X drive shaft. It is a figure which illustrates the common speed pattern of a Y drive shaft. It is a figure which illustrates the common speed pattern of a Z drive shaft. It is a figure which illustrates the common speed pattern of the 1st rotation mechanism part 510. It is a figure which illustrates the common speed pattern of the 2nd rotation mechanism part 520. It is a figure which showed typically the state of calculating the interpolation point of the X drive axis in order. It is a figure which shows the position of the rotation center Qp0 when the 1st rotation angle α = 2nd rotation angle β = 0 in a probe coordinate system. It is a figure for demonstrating the conversion formula which obtains the position of the rotation center Qp when the 1st rotation angle is α and the 2nd rotation angle is β in a probe coordinate system. It is a figure which shows typically how the coordinate of the rotation center Qp in a probe coordinate system is converted into a work coordinate system. It is a figure which shows typically how the coordinate of the rotation center Qw in a work coordinate system is converted into a machine coordinate system. As a inverse proportion, it is a figure which schematically exemplifies the trajectory of the rotation center Q when the 1st rotation mechanism part and the 2nd rotation mechanism part are not synchronized with the X, Y, Z drive shafts. It is a figure which shows the mode that only the posture of a probe head is changed while the displacement of a measuring tip remains zero.

An embodiment of the present invention will be illustrated and described with reference to the reference numerals attached to each element in the drawing.
(First Embodiment)
FIG. 2 is a diagram showing the overall configuration of the shape measuring system 100.
Although the configuration itself of the shape measurement system 100 is known, it will be briefly described.
The shape measurement system 100 includes a three-dimensional measuring machine 200, a motion controller 300 that controls the driving of the three-dimensional measuring machine 200, and a host computer 400 that controls the motion controller 300 and executes necessary data processing.

The coordinate measuring machine 200 includes a surface plate 210, a moving mechanism 220, and a probe head 500.

The moving mechanism 220 is fixed to a gate-shaped Y slider 231 provided so as to be slidable on the surface plate 210 in the Y direction, an X slider 241 that slides along the beam in the X direction of the Y slider 231 and an X slider 241. The Z-axis column 251 is provided, and the Z-spindle 252 that moves up and down in the Z-axis column 251 in the Z direction is provided.

A drive motor (not shown) and an encoder (not shown) are attached to the Y slider 231 and the X slider 241 and the Z spindle 252, respectively.
Each drive motor is drive-controlled by a drive control signal from the motion controller 300. The encoder detects the movement amount of each of the Y slider 231 and the X slider 241 and the Z spindle 252, and outputs the detected value to the motion controller 300.
A probe head 500 is attached to the lower end of the Z spindle 252.

In the following description, the drive mechanism for driving the Y slider 231 is referred to as the Y drive shaft 230, the drive mechanism for driving the X slider 241 is referred to as the X drive shaft 240, and the drive mechanism for driving the Z spindle 252 is referred to as Z drive. It will be referred to as the shaft 250.
The drive mechanism referred to here means, for example, a combination of a ball screw and a motor.

FIG. 3 shows a cross-sectional view of the probe head 500.
The probe head 500 includes a head fixing portion 501, a first rotation mechanism portion 510, a second rotation mechanism portion 520, and a stylus 502 having a measuring tip 503 at the tip.

The head fixing portion 501 is attached to the lower end of the Z spindle 252.
Further, a first rotation mechanism portion 510 is provided at the lower end of the head fixing portion 501.
The first rotation mechanism unit 510 includes a first housing 511, a first motor 512, and a first shaft 513.
The first housing 511 is attached to the lower end of the head fixing portion 501.
The first motor 512 is installed inside the first housing 511, and the first shaft 513 is attached to the armature of the first motor 512.
Now, the rotation axis of the first shaft 513 is referred to as the first rotation axis A1.
In the present embodiment, the axial direction of the first rotation axis A1 coincides with the Z-axis direction.

The second rotation mechanism unit 520 includes a second housing 521, a second motor 522, a second shaft 523, and a U-shaped connecting frame 524.
The second housing 521 is connected to the first shaft 513.
The second motor 522 is internally installed in the second housing 521, and the second shaft 523 is attached to the armature of the second motor 522.

Now, the rotation axis of the second shaft 523 is referred to as the second rotation axis A2. At this time, the first rotation axis A1 (extension line) and the second rotation axis A2 are orthogonal to each other. A U-shaped connecting frame 524 is attached to the second shaft 523, and the U-shaped connecting frame 524 rotates about the second rotating shaft A2 as the center of rotation.

A stylus 502 is attached to the lower end of the U-shaped connecting frame 524. The axis A3 (extension line) of the stylus 502 is orthogonal to the second rotation axis A2.

Now, the first rotation axis A1 (extension line), the second rotation axis A2, and the axis A3 (extension line) of the stylus 502 intersect at one intersection.
For the following explanation, this intersection will be named the center of rotation Q.

Further, the rotation angle of the first rotation axis A1 is represented by α, and it is assumed that −180 ° ≦ α ≦ 180 °.
(If an electrical connection can be made, there is no need to set a limit on the movable range, and the rotation operation itself may rotate any number of times.)
In FIG. 2 or 3, it is assumed that the front side is 0 °, the counterclockwise rotation is the positive direction rotation, and the clockwise rotation is the negative direction rotation when viewed from above.

The rotation angle of the second rotation axis A2 is represented by β, and it is assumed that 0 ° ≦ β ≦ 90 °. When the stylus 502 is vertically downward, it is defined as 0 °. Of course, it is arbitrary where the 0 ° reference is taken.

It is assumed that the first motor 512 and the second motor 522 are, for example, stepping motors and are driven in synchronization with the applied drive pulse. That is, the momentum (rotation angle) of the first rotation mechanism unit 510 and the second rotation mechanism unit 520 is proportional to the number of drive pulses.

Further, the probe head 500 includes a probe sensor (not shown) that detects the displacement of the stylus 502 in order to detect the contact between the measuring tip 503 and the work surface. The probe sensor outputs the detected value to the motion controller 300.

In the following description, in addition to the first rotation mechanism unit 510 and the second rotation mechanism unit 520, the X drive shaft, the Y drive shaft, and the Z drive shaft are also driven by drive pulses, and the first rotation mechanism unit 510 and the second It is assumed that the response characteristics of the rotation mechanism unit 520, the X drive shaft 240, the Y drive shaft 230, and the Z drive shaft 250 are the same.
Hereinafter, the control method of the present embodiment will be described on the premise that the response characteristics of the five axes are the same.
If there is a difference in the response characteristics of the five axes, adjust the control gain of the element with the delay.

The host computer 400 receives CAD data (for example, NURBS (Non-UniformRational B-Spline) data) including route information from an external CAD system or the like, and creates measurement route information.
The created measurement path information is given to the motion controller 300, and the motion controller 300 drives each drive axis of the coordinate measuring machine 200 and the probe head 500 so that the measuring tip 503 traces the surface of the work and measures along the measurement path. Control.

(Control method of shape measuring device)
Hereinafter, a control method of the shape measuring device according to the present embodiment will be described.
Before explaining the specific control steps, the operation of the shape measuring device aimed at by the present embodiment will be outlined.
For example, consider moving the probe head 500 from the first point P1 to the second point P2, as illustrated in FIG.
(At this time, not only the three-dimensional positions (X, Y, Z) but also the postures (α, β) of the probe head 500 change.)
When the probe head 500 changes its position while changing its posture, the first rotation mechanism unit 510 and the second rotation mechanism unit 520 also rotate. Therefore, simply considering, the movement locus of the measuring tip 503 is linear. Must not be.
In this respect, in the present embodiment, the movement path of the measurement chip 503 can be easily predicted. Specifically, the locus of movement of the measuring chip 503 is set to be a straight line.

Specific control steps will be described in order with reference to the flowcharts (FIGS. 5 and 7).
The operations of FIGS. 5 and 7 are mainly executed by the motion controller 300.

First, in ST100, the motion controller 300 sequentially reads the measurement path information received from the host computer 400, and reads the next target position He (Twex, Twee, Twez, αe, βe).
Here, in controlling the movement and posture of the probe head 500, not only the three-dimensional coordinate positions (x, y, z) but also the posture of the probe head 500 (first rotation mechanism unit 510 and second rotation mechanism) The target angle (α, β) of part 520 is also required.

The coordinate position (x, y, z) and the posture (α, β) are combined, and the name “position” is used.
If we simply want to represent a three-dimensional coordinate position (x, y, z), we will call it "position".
Further, various coordinate systems such as a work coordinate system, a probe coordinate system, and a machine coordinate system are required for operation control of the coordinate measuring machine 200 and the probe head 500.
When it is necessary to clarify the type of the coordinate system, it is clearly stated, but when it is not necessary to distinguish the coordinate system or when it is clear from the context before and after, the type of the coordinate system may be omitted.

In the command given from the host computer 400 to the motion controller 300, the three-dimensional coordinate position is given as the coordinate Twi of the measurement chip 503 in the work coordinate system.
Twi = (Twix, Twiy, Twiz)
The current position is represented by Tws = (Twsx, Twsy, Twsz), and the target position is represented by Twe = (Twex, Twee, Twez) (see FIG. 6).

Further, the target angles (α, β) of the first rotation mechanism unit 510 and the second rotation mechanism unit 520 are given by the probe coordinate system.
The position (location) of the work coordinate system and the angle of the probe coordinate system are combined to form the position Hi (Twix, Twiy, Twix, αi, βi).
The current position is Hs (Twsx, Twsy, Twsz, αs, βs), and the target position is He (Twex, Twee, Twez, αe, βe).

When the next target position He (Twex, Twee, Twez, αe, βe) can be set (ST100), then the motion controller 300 drives and controls each drive axis so as to reach the target position. Generate a pattern (ST110).
The speed pattern generation procedure (ST110) will be described with reference to the flowchart of FIG.

In ST111, the motion controller 300 plans a speed pattern for each drive shaft.
This process itself is the same as before.
The current position Hs (Twsx, Twsy, Twsz, αs, βs) and the target position He (Twex, Twee, Twez, αe, βe) are given. It starts moving from the initial speed of zero at the current position, accelerates, shifts to a constant speed when the upper limit speed is reached, then decelerates and stops at the target position. Various methods for generating such a velocity pattern are known (for example, Japanese Patent Application Laid-Open No. 2014-48095).

Now, suppose that the speed pattern for each drive shaft is obtained as shown in FIGS. 8 to 12.
8, 9, and 10 are speed patterns of the X drive shaft 240, the Y drive shaft 230, and the Z drive shaft 250 of the coordinate measuring machine 200, respectively.
(Specifically, it is a moving speed pattern of the X slider 241 and the Y slider 231 and the Z spindle 252.)
For example, FIG. 8 is a speed pattern of the X drive shaft 240.
It accelerates to time ta (X), reaches the upper limit speed, shifts to constant speed, and stops at time te (X).
The subscript notation rules are unified in FIGS. 8, 9 and 10, and redundant explanations are omitted.

When there is a constant speed movement region as in the speed pattern of FIG. 8 (X drive shaft 240) and FIG. 9 (Y drive shaft 230), such a movement mode is referred to as a trapezoidal mode.
Further, as in the speed pattern of FIG. 10 (Z drive shaft 250), when deceleration is started before the upper limit speed is reached and there is no constant speed movement region, such a movement mode is referred to as a triangular mode. To do.

Similarly, FIGS. 11 and 12 are speed patterns of the first rotation mechanism portion 510 and the second rotation mechanism portion 520 of the probe head 500, respectively.
(Specifically, it is the rotational angular velocity of the first motor 512 and the second motor 522.)

After the speed pattern for each drive axis is obtained as shown in FIGS. 8 to 12, the process of synchronizing all the axes is performed next.
In ST112, the motion controller 300 identifies the drive shaft having the maximum required time.
Compare te (X) to te (A2) and identify the longest one.
Here, it is assumed that the moving distance in the X-axis direction is the longest and te (X) is the longest. Then, the parameter of the drive shaft having the maximum required time te is set as a common parameter (ST113).

As common parameters, the common movement time tec, the common movement mode, the common acceleration time tac, and the common deceleration time tdc are determined.
Here, from the speed pattern of the X drive shaft 240, the common movement time tec is the movement time te (X) of the X drive shaft, the common movement mode is the trapezoidal mode, and the common acceleration time tac is ta (X). , The common deceleration time tdc is td (X).

Next, in ST114, a common speed pattern is calculated for each drive shaft.
Since the common parameters are originally used for the speed pattern of the X drive shaft 240, which has the maximum required time, it can be left as it is (FIG. 13).
For speed patterns other than the X drive shaft, the movement time te, the movement mode, the acceleration time ta, and the deceleration time td are made to be aligned with the common parameters (FIGS. 14 to 17).
For example, the second rotation mechanism unit 520 will be described as an example (FIG. 17).
The original movement mode of the second rotation mechanism unit 520 was the triangular mode, but this is changed to the trapezoidal mode. Then, the acceleration time ta (A2) is set to the common acceleration time tac, the deceleration time td (A12) is set to the common deceleration time tdc, and the movement time te (A2) is set to the common movement time tec.
However, since the movement distance (rotation angle) must be stored as it is, the magnitude of acceleration is adjusted so that the movement distance (rotation angle) is the same before and after standardization.
In this way, a velocity pattern (FIGS. 13 to 17) in which the five axes are synchronized with common parameters can be obtained.

Since the velocity pattern in which the five axes are synchronized with the common parameters can be generated (FIG. 7), the process returns to FIG. 5 and then the target interpolation point for each control cycle is calculated (ST120).
That is, assuming that one control cycle of the motion controller 300 is Δt, the target point for each control cycle is calculated for each drive axis.
The target point for each control cycle is referred to as an interpolation point.
Let n be the quotient when the common travel time tec is divided by the control cycle Δt.
n = (tec / Δt)
The interpolation point can be obtained by dividing the time of the speed pattern of the five drive shafts into n equal parts and adding the increments in one control cycle Δt in order.

FIG. 18 is a diagram schematically showing how the interpolation points of the X drive shaft are calculated in order.
In FIG. 18, the displacement amount ΔTwix in one control cycle Δt is calculated by ((V _{x (i-1)} + V _xi ) × Δt / 2), but as V _{x (i-1)} × Δt. It may be Vi × Δt, or when the velocity pattern is given by a curve, it may be calculated (integrated) more precisely.
In this way, the interpolation point can be obtained for each drive axis.
Hi (Twix, Twiy, Twiz, αi, βi)

The interpolation point Hi (Twix, Twiy, Twiz, αi, βi) was calculated in ST120, but Twi (Twix, Twiy, Twiz) is given as a point in the work coordinate system.
In the drive control of the coordinate measuring machine 200, it is necessary to convert it into a command of the machine coordinate system. The command is given as the coordinates of the measuring tip 503 in the work coordinate system. This, in the present embodiment, converts the coordinate of the rotation center _{Q M} of the probe head 500 in the machine coordinate system (ST130).

Note that represents the position of the center of rotation Q of the probe head 500 as viewed in the machine coordinate system Q _M.
The position of the rotation center Q of the probe head 500 when viewed in the work coordinate system is represented by Q _W. Further, representative of the position of the center of rotation Q of the probe head 500 as viewed in the probe coordinate system Q _P.

The conversion formula will be explained.

First, in the probe coordinate system, consider how the rotation center Qp is represented with respect to the first rotation angle α and the second rotation angle β.
Now, let the origin of the probe coordinate system be the measurement chip 503 (center), and the coordinates of the rotation center Q when the first rotation angle α = the second rotation angle β = 0 be Qp0 (Qpx0, Qpy0, Qpz0). (See FIG. 19). Then, it is assumed that the coordinates of the rotation center Q when the first rotation angle is α and the second rotation angle is β are represented by Qp (Qpx, Qpy, Qpz) (FIG. 20).
At this time, the position of the rotation center Qp at the first rotation angle α and the second rotation angle β is such that Qp0 (Qpx0, Qpy0, Qpz0) is rotated α around the first rotation axis and β around the second rotation axis. (See, for example, FIG. 20).

For example, suppose that the coordinate Qp0 of the rotation center Q when the first rotation angle α = the second rotation angle β = 0 is (0, 0, L).
At this time, the coordinates Qp (Qpx, Qpy, Qpz) of the rotation center Q when the first rotation angle α and the second rotation angle β are arbitrary are as follows.

Earlier, the interpolation point Hi (Twix, Twiy, Twiz, αi, βi) was obtained as a target point for each control cycle Δt.
It is necessary to calculate the rotation center Qwi corresponding to each control interpolation point Hi.

For the first rotation angle α and the second rotation angle β, αi and βi have already been obtained as interpolation points for each control cycle.
The interpolation point Qpi (Qpix, Qpiy, Qpiz) of the rotation center Qpi in the probe coordinate system is obtained by using the first rotation angle αi and the second rotation angle βi at that time.

Since the coordinates of the rotation center Qpi (Qpix, Qpiy, Qpiz) are in the probe coordinate system (coordinate system with the measurement tip 503 as the origin), this is copied to the work coordinate system for the time being.
The coordinates of the rotation center Qwi (Qwix, Qwiy, Qwiz) in the work coordinate system are as follows (see FIG. 21).

Here, it is assumed that only the origin is deviated between the probe coordinate system and the work coordinate system, and the x-axis, y-axis, and z-axis of both coordinate systems are parallel to each other. If the direction of the axis is also different between the probe coordinate system and the work coordinate system, a rotation element is also required.

Qwi = Twi + Qpi
(Qwi, Twi, Qpi are vectors)
The components are explicitly expressed as follows.

Now that the rotation center Qwi in the work coordinate system has been obtained, these are converted into the machine coordinate system (see FIG. 22). The transformation from the work coordinate system to the machine coordinate system is represented by the affine transformation ^M f _W.

Q _Mi = ^M f _W · Qwi
(Q _Mi and Qwi are vectors)

Converting ^M f _W from the workpiece coordinate system to the machine coordinate system is a synthesis of rotational movement and translation, the displacement of the origin between the vector Ow, if a rotation matrix and ^M C _W, expressed as follows ..
_{^{Q Mi = [M C W]}} Qwi + Ow
With this, the control interpolation point Q _Mi in the machine coordinate system can be obtained.

The obtained control interpolation point Q _Mi is registered in a memory (not shown) (ST140), and positioning control is sequentially performed on the control interpolation point Q _Mi stored in the memory (ST150). The difference between the current position and the target position is obtained for each drive axis, and the motor of each axis is driven by the drive pulse according to the difference.

When this control is executed, the movement locus of the measuring chip 503 becomes a straight line.
I will explain the meaning of the calculation by looking back a little.
When shifting from the current position Hs (Twsx, Twsy, Twsz, αs, βs) to the target position He (Twex, Twee, Twez, αe, βe), when only the position information (location information) is extracted, the current position Tws This is the displacement from (Twsx, Twsy, Twsz) to the target position Twe (Twex, Twsy, Twez) (see FIG. 6).
To displace the probe head 500 from the current position Tws (Twsx, Twsy, Twsz) to the target position Twe (Twex, Twee, Twez), the X drive shaft 240, Y drive shaft 230 and Z drive shaft of the CMM 200 Drive 250.
At this time, in the present embodiment, in generating the speed pattern (ST110), the common parameter was determined in ST113, and the common speed pattern using the common parameter was obtained in ST114.

By the way, considering only to make the movement locus of the measurement chip 503 straight, it is necessary to make the speed patterns common for the X drive shaft 240, the Y drive shaft 230, and the Z drive shaft 250 with common parameters. It is not necessary to standardize the 1-rotation mechanism unit 510 and the 2nd rotation mechanism unit 520.
The advantages of sharing the speed pattern of the first rotation mechanism unit 510 and the speed pattern of the second rotation mechanism unit 520 will be described later.

According to the common speed pattern, the X drive shaft 240, the Y drive shaft 230, and the Z drive shaft 250 start moving at the same time, accelerate and decelerate for the same time, and stop at the target position at the same time.
By synthesizing the three-axis synchronized movements in this way, a linear path from the current position Tws (Twsx, Twsy, Twsz) to the target position Twe (Twex, Twee, Twez) is created (see FIG. 6).

Then, assuming that one control cycle of the motion controller 300 is Δt, the interpolation points for each control cycle were obtained for each drive axis.
Hi (Twix, Twiy, Twiz, αi, βi)

Now, the locus of Ti (Twix, Twiy, Twiz) is a straight line. Then, the first rotation angle αi and the second rotation angle βi in the i-th control cycle are given as (αi, βi). At that time, the coordinate Ti of the measuring chip 503 is converted into the coordinate Qi of the rotation center of the probe head 500 in consideration of the first rotation angle αi and the second rotation angle βi at that time. If the control interpolation points Q _Mi (Q _Mix , Q _My , Q _Miz , α _i , β _i ) obtained in this way are set as the positioning target points, it is natural that the movements of the five axes are combined. , The locus of the measuring chip 503 becomes a straight line.
(Of course, the locus of the rotation center Q of the probe head 500 can be a curved line instead of a straight line.)

As described above, according to the present embodiment, since the movement path of the measurement chip 503 is simplified (specifically, a straight line) and can be predicted, the measurement part program (measurement location of the work, measurement path, etc.) is incorporated into the measurement. It becomes easier to create a control program). Then, unintended interference between the measuring tip 503 (or stylus 502) and the work is eliminated.

(Modification example 1)
The moving mechanism 220 of the coordinate measuring machine 200 may originally have three-axis synchronous control.
In this case, the speed pattern of the moving mechanism 220 of the coordinate measuring machine 200 is originally obtained as a speed pattern of the combined speed Vsync in which the speeds of the X drive shaft 240, the Y drive shaft 230, and the Z drive shaft 250 are combined.
In this case, the procedure (ST112-ST114) for sharing the speed patterns of the X drive shaft 240, the Y drive shaft 230, and the Z drive shaft 250 is not necessary, but conversely, when calculating the control interpolation point, the X direction, It is necessary to decompose in the Y direction and the Z direction.
Now, let the movement amount ΔTsynci per control cycle Δt be ((V sin _(i-1) + _Vsini ) / 2) × Δt.
Further, the direction cosine of the linear movement from the current position Tws (Twsx, Twsy, Twsz) to the target position Twe (Twex, Twee, Twez) is defined as (I, J, K).
At this time, ΔTwxi = I · ΔTsyni, ΔTwyi = J · ΔTsyni, ΔTwzi = K · ΔTsyni.
Therefore, the control interpolation points Twix, Twiy, and Twix are as follows.

T _wix = T _{w (i-1) x} + ΔT _wix = T _{w (i-1) x} + I · ΔTsyni
T _wy = T _{w (i-1) y} + ΔT _wy = T _{w (i-1) y} + J · ΔTsyni
T _wiz = T _{w (i-1) z} + ΔT _wiz = T _{w (i-1) z} + K · ΔTsyni

(Modification 2)
In the above embodiment, the command given as the coordinates of the measurement chip 503 is converted into the coordinate value of the rotation center Q of the probe head 500, and the rotation center Q is set as the control target point.
On the other hand, in calculating the speed pattern (ST111), the movement of the measurement chip 503 is used as a reference. Therefore, there is no guarantee that the speed of the rotation center Q after the conversion process is within the maximum speed, and there is a possibility that the speed of the rotation center Q exceeds the maximum speed. In this case, it is necessary to back-calculate and correct the moving speed of the measuring chip 503 in consideration of the maximum speed of the rotation center Q.

For example, a part or the whole of the orbit of the rotation center Q is a curved orbit, and its acceleration (centrifugal force) may exceed the withstand acceleration of the coordinate measuring machine 200. Therefore, the radius of curvature r is obtained for each part of the orbit (curve), and the acceleration of the center of rotation of the probe head 500 is obtained from each radius of curvature r and the velocity V at that time, and if this acceleration is the resistance of the three-dimensional measuring machine 200. When the acceleration a is exceeded, it is necessary to recalculate the velocity pattern of the measuring chip 503 so as to limit the maximum velocity V _Qmax to V _Qmax ≤ √ (a · r).

Here, the necessity of standardizing the speed pattern not only for the X, Y, and Z drive shafts 230-250 but also for the first rotation mechanism unit 510 and the second rotation mechanism unit 520 will be described.
Considering only to make the movement locus of the measuring chip 503 a straight line, it is sufficient to synchronize the three axes of the X drive shaft 240, the Y drive shaft 240, and the Z drive shaft 250. However, if the first rotation mechanism unit 510 and the second rotation mechanism unit 520 are not synchronized, it is considered that the possibility that the curvature of the orbit of the rotation center Q becomes tight (the curvature becomes large) increases.
For example, it is assumed that the speed patterns of the first rotation mechanism unit 510 and the second rotation mechanism unit 520 are left as they are in FIGS. 11 and 12 and are not standardized.
Then, the orbit of the rotation center Q is expected to move on the straight line LP1 after passing through the curved orbit CP1 as shown in FIG. 23, for example.

At first, since there is a coordinate conversion for the rotation of the first rotation mechanism part 510 and the second rotation mechanism part 520, the trajectory of the rotation center Q becomes like the curve CP1, and then the first rotation mechanism part 510 is also the first. When the two-rotation mechanism unit 520 is also stopped, only the X drive shaft 230, the Y drive shaft 240, and the Z drive shaft 250 are driven, so there is no contribution of rotation, and the orbit of the rotation center Q will be just a straight line LP1.

If the orbit of the center of rotation Q has a curved orbit with a large curvature or a sudden change of direction, the acceleration of the center of rotation Q will exceed the withstand acceleration of the coordinate measuring machine 200.
On the other hand, if all five axes are synchronized as in the above embodiment, the locus of the rotation center Q becomes a gentle curve as a whole (see FIG. 21 or FIG. 22), and the acceleration of the rotation center Q is measured three-dimensionally. The possibility of exceeding the withstand acceleration of the machine 200 is reduced. Therefore, when considering not only the problem of a simple mathematical solution but also the driving performance (for example, acceleration resistance performance) of the actual coordinate measuring machine 200, it can be said that it is preferable to synchronously control all five axes.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit.
In the above embodiment, the case where the movement locus of the measurement chip 503 is a straight line is illustrated.
Here, although the position of the measurement chip 503 does not change, there may be a case where it is desired to change only the posture of the probe head 500, as illustrated in FIG. 24, for example.
If the conventional technique is applied as it is, even if the measuring tip 503 finally returns to the same position, the measuring tip 503 (stylus 502) is moved to the first rotation mechanism part 510 and the second rotation mechanism part in the middle of the process. It is expected to be swung considerably with the rotation of 520.
Since the operator does not recognize that the measuring tip 503 is being moved, it may not be thought that the measuring tip 503 (or stylus 502) interferes with the work, but in reality, the measuring tip 503 (stylus 502) Will move considerably, which may cause interference between the measuring tip 503 (or stylus 502) and the workpiece.
On the other hand, when the present invention is applied, only the posture of the probe head 500 can be changed without the measuring tip 503 moving at all.
Therefore, the measuring tip 503 (or stylus 502) and the work do not interfere unintentionally.

The point of the present invention is to convert the command given as the coordinate value of the measurement chip into the coordinates of the rotation center Q by a conversion formula that takes into account the first rotation angle αi and the second rotation angle βi, and to convert the coordinates of the rotation center Q. It is at the point to be the control interpolation point Qi.
For example, the operator may arbitrarily set the movement locus of the measuring chip, such as a straight line, an arbitrary arc, or a bent straight line.
At that time, if the control interpolation point Qi is obtained by the conversion incorporating the first rotation angle αi and the second rotation angle βi at that time, and the X, Y, and Z drive axes set the control interpolation point Qi as the positioning target, The movement trajectory of the measuring chip is as intended by the operator.

100 ... shape measurement system, 200 ... three-dimensional measuring machine, 210 ... platen, 220 ... moving mechanism, 230 ... Y drive shaft, 231 ... Y slider, 240 ... X drive shaft, 241 ... X slider, 250 ... Z drive shaft , 251 ... Z-axis column, 252 ... Z spindle, 300 ... motion controller, 400 ... host computer, 500 ... probe head, 501 ... head fixing part, 502 ... stylus, 503 ... measuring chip, 510 ... first rotation mechanism part, 511 ... 1st housing, 512 ... 1st motor, 513 ... 1st shaft, 520 ... 2nd rotation mechanism, 521 ... 2nd housing, 522 ... 2nd motor, 523 ... 2nd shaft, 524 ... U-shaped connecting frame ..

Claims (6)

A stylus having a measuring chip at the tip, a first drive shaft that is rotationally driven around the first rotary shaft, and a second drive shaft that is rotationally driven around a second rotary shaft that is orthogonal to the first rotary shaft. A probe head that has and changes the posture of the stylus by the rotational movement of the first drive shaft and the second drive shaft.
A three-dimensional measuring machine having a third drive shaft, a fourth drive shaft, and a fifth drive shaft as three translational axes orthogonal to each other and three-dimensionally displacing the position of the probe head is provided.
The position of the measuring chip is given by the coordinate values (T3, T4, T5) of the third to fifth drive shafts, and the posture of the probe head is the first rotation angle α of the first drive shaft and the said. It is a control method of the shape measuring device given by the second rotation angle β of the second drive shaft.
The movement route starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) to the target position He (Te3, Te4, Te5, αe, βe) is set by the operator.
In the movement path from the current position Hs (Ts3, Ts4, Ts5, αs, βs) to the target position He (Te3, Te4, Te5, αe, βe), the interpolation points for each control cycle are set from the first to the first. Obtained for each of the 5 drive shafts
When the intersection of the first rotation axis and the second rotation axis is the rotation center Q, the above-mentioned is described by a predetermined conversion formula in which the values of the interpolation points (αi, βi) of the first and second drive axes are taken into consideration. The coordinate value of the intersection point of the measurement chip is converted into the coordinate value of the rotation center Q to obtain the control interpolation point Qi.
For each control cycle, the third to fifth drive shafts are positioned and controlled at the control interpolation point Qi, and the first and second drive shafts are the interpolation points (αi,) of the first and second drive shafts. A control method for a shape measuring device, characterized in that positioning control is performed on βi). In the control method of the shape measuring device according to claim 1,
The movement path starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) is set as a linear movement path. A control method for a shape measuring device, characterized in that it is present. In the control method of the shape measuring device according to claim 1,
The movement path starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) is set as a bent linear movement path. A control method for a shape measuring device, characterized in that it is used. In the control method of the shape measuring device according to claim 1,
The movement path starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) is set as an arc-shaped movement path. A control method for a shape measuring device, characterized in that it is used. In the control method of the shape measuring device according to any one of claims 1 to 4.
Velocity patterns starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) are generated for each of the first to fifth drive shafts.
For the speed patterns generated for the third to fifth drive shafts, a common speed pattern is set for each of the third to fifth drive shafts so as to synchronize with a common acceleration / deceleration time and a common required time. A control method for a shape measuring device, characterized in that it is generated. In the control method of the shape measuring device according to any one of claims 1 to 5 .
Velocity patterns starting from the current position Hs (Ts3, Ts4, Ts5, αs, βs) and reaching the target position He (Te3, Te4, Te5, αe, βe) are generated for each of the first to fifth drive shafts.
A common speed pattern is generated for each of the first to fifth drive shafts so that the speed patterns generated for each of the first to fifth drive shafts are synchronized with a common acceleration / deceleration time and a common required time. A control method for a shape measuring device.