JP2007057308A - Contact type probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a probe which scans stably even if refuse exists on the measuring object surface, in shape measurement by a contact type probe. <P>SOLUTION: A force generation means for applying a force to a probe shaft in the fixed state to a housing is provided, and the force applied to the probe shaft is changed by displacement or speed between the housing and the probe shaft, to thereby enable stable scanning. Namely, when tracing is performed normally, a force as a weak spring element is applied to the probe shaft, and when being sprung up by refuse or the like, the probe is returned quickly onto the measuring surface by enhancing rigidity of the spring element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The three-dimensional measuring apparatus can be divided into two types: a probe that traces the shape of the object to be measured and a coordinate measuring means that measures the position of the probe. At this time, what is important for the probe is to pass the surface position of the object to be measured to a member capable of measuring coordinates. An error when the probe traces the surface of the object to be measured is called a trace error. Conventionally, as disclosed in Japanese Patent Laid-Open No. 6-265340, a probe shaft is provided so as to be movable up and down using an air bearing, and its own weight is supported by a spring. In addition, the 1992 Precision Engineering Society Spring Conference Academic Lecture Proceedings p697 also proposes a configuration in which a probe shaft is provided so that it can be moved up and down using an air bearing and its own weight is supported by a spring.

  When tracing a shape using such a probe, the aforementioned trace error occurs. A sufficiently weak spring, that is, a spring constant needs to be sufficiently small so that a probe pressing force error does not occur even if there is a trace error. This is because the amount obtained by multiplying the trace error by the spring constant is an error in the pressing force.

  As another conventional example, Japanese Patent Publication No. 2003-42742 discloses a method of canceling the weight of a probe using magnetic force. In this method, a magnetic circuit composed of a yoke, a permanent magnet and a coil is fixed so that the yoke sandwiches the probe, and its own weight is canceled by a magnetic force generated between the yoke and the probe.

In addition, the probe is often called a stylus, a stylus, or a feeler.
Japanese Patent Laid-Open No. 06-265340 JP 2003-42742 A

  However, the conventional example has a problem that it is easily affected by dust on the surface of the measurement object.

  FIG. 5 is a diagram schematically showing a conventional contact probe. A probe 122 is movably arranged in one direction at the tip of a moving member 123 such as a measurement axis that can be moved three-dimensionally. Has a sphere 121 at its tip and is suspended from a moving member 123 by a spring 124. This spring 124 is a very weak spring so as not to cause a trace error.

  When the object to be measured is scanned using such a probe, it can be considered that dust, dust or the like adhering to the surface of the measurement surface collides with the tip of the probe, and the probe jumps up above the measurement surface. When it is flipped up, it vibrates at the natural frequency calculated from the probe mass and the spring coefficient. If the spring stiffness is reduced in order to reduce the pressing force, it takes time for the probe to return to the measurement surface again. The data in the flying section becomes an abnormal value and cannot be used as a measurement result. In order to shorten the flying section, it is necessary to reduce the scanning speed. However, this extends the measurement time, resulting in problems such as deterioration in measurement accuracy and increase in measurement cost.

  Furthermore, since the trace control adjustment is performed with the probe and measurement surface in contact correctly, if the probe and measurement surface are separated for a certain period of time, the control system will break down and measurement will continue. It becomes impossible and the measurement has to be repeated from the beginning. This leads to an increase in measurement cost.

  For example, if the probe mass is 10 g and the spring constant is K = 0.001 mN / μm, the natural frequency of the probe portion is very low, sqrt (K / M) /2π=1.6 Hz. If it is considered that it is half of the natural frequency period that the probe is returned to the measurement surface again, it will be about 1 / 1.6Hz / 2 ≒ 0.3S. The probe is away from. For example, if scanning is performed at a scanning speed of 10 mm / s, the probe is about 3 mm apart in the scanning direction during that time, and the measurement result obtained in this section cannot be used as an abnormal value.

  An object of the present invention has been made in view of such a situation, and is to reduce the influence of dust on the surface of a measurement object.

  The operation of the present invention will be described with reference to FIG.

  As shown in the figure, the probe 122 is provided so as to be movable in one direction (Z direction in FIG. 4) with respect to the moving member 123, and the probe 122 is suspended from the moving member 123 in the moving direction. In addition, a voice coilless motor including a magnet 113 and a coil 114 is provided so that force can be applied from the moving member 123 to the probe 122 in the probe moving direction. Here, the voice coilless motor including the coil 114 and the magnet 113 is controlled by the following control law using the current control device 115.

  Here, F represents the generated force of the voice coilless motor, K represents the set spring constant, C represents the set viscosity coefficient, and x represents the relative displacement between the moving member 123 and the probe 122.

  The set spring constant K and set viscosity coefficient C in the above equation can be freely set by software. It is also possible to switch the value according to various situations during measurement.

  For example, when the surface of the object to be measured can be normally scanned, it is convenient if the set spring constant K is set to a weak value because scanning can be performed accurately without being affected by the trace error.

  However, when the probe is flipped up by dust or the like and separated from the surface to be measured, it takes time for the probe to return to the measurement surface again if the set spring rigidity remains weak. In order to prevent this, it is clear that it is convenient to change the set rigidity and the set viscosity only when it is flipped up. For example, if the set rigidity is increased only when the probe is flipped up, the natural frequency of the probe increases, so that the probe can be quickly returned to the measurement surface. In addition, since the set viscosity and set stiffness can be set freely, the attenuation ratio can be set after all. However, if the attenuation ratio is increased, the probe will jump up again when the probe returns to the measurement surface. Also disappear.

  As described above, according to the present invention, it is possible to apply a spring-like force or a viscous-like force to the probe according to the situation by the force generation mechanism added to the probe. Moreover, the trace can be stabilized by switching the set stiffness of the spring element force and the set viscosity of the viscous element force by the probe displacement. That is, when the measurement surface is normally traced, it operates as a weak spring element, and when the probe is flipped up by dust on the measurement surface, the set frequency is changed to increase the natural frequency. By returning the probe to the measurement surface quickly and adjusting the set viscosity, it is possible to prevent the probe from jumping up again upon landing.

Example 1
Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a partially broken shape measuring apparatus incorporating a contact probe according to an embodiment of the present invention, FIG. 2 is a measurement flow thereof, and FIG. 3 is incorporated in a probe shaft. It is a control flow of a force generation element.

  In FIG. 1, a probe tip 2 having a conical tip for attaching a sphere 1 is screwed and fixed to the lower side of the probe shaft 4 with a spacer 3 interposed therebetween. Further, the mirror 6 is bonded and fixed to the mirror fixing piece 5, and is fixed by screwing on the upper side of the probe shaft 4 with an iron core holder inserted with an iron core 19 having two permanent magnets 18 bonded to both ends.

  Further, the yoke 17 is fixed to the second housing 16 via the yoke connecting jig 7. The yoke 17 has a box-like configuration, and a magnetic circuit is formed by the permanent magnet 18, the iron core 19, and the yoke 17. Further, the inner surface of the yoke facing the permanent magnet is provided with a curvature in the probe moving direction.

  Here, although the operation of the magnetic circuit will not be described in detail, the magnetic circuit can generate the following force by making the yoke 17 an appropriate shape.

F = + 0.06467-11.14z (however, F [N], Z [m])
Formula (1)
It becomes. In the equation, z is a relative displacement between the probe shaft 4 and the housing 10.

  The first term in Equation (1) is a term that generates a force that supports the weight of the probe shaft 4 with a constant value. The second term includes the amount of movement z of the probe shaft 4 and indicates that the force decreases as z increases. Since the generated force changes as the probe shaft is displaced, it can be said that a mechanical spring is formed.

  The probe shaft 4 is supported so as to be movable in the vertical direction with respect to the housing 10 via a so-called air bearing 11 that supports the probe shaft 4 in a non-contact manner through a thin air film. A compressed air hole 12 is formed to guide the compressed air. These compressed air holes 12 can be freely drawn around the inside of the housing 10 by drilling from one side with a drill and closing the surface portion of the hole with screws or an adhesive as necessary. The compressed air hole 12 is connected to a compressed air pipe 13 and further connected to a compressed air source (not shown). With this configuration, the probe shaft 4 can freely move in the vertical direction without friction.

  The housing 10 is provided with a protruding lower stopper 10 b on the lower surface thereof, and restricts excessive movement of the probe shaft 4 in the upward direction by colliding with the spacer 3. Similarly, a protrusion-shaped upper stopper 10a is provided on the upper surface of the housing 10 for excessive movement in the downward direction, and abuts against a protrusion provided on the probe shaft 4. The housing 10 is fixed and supported by a second housing 16 fixed to the measurement shaft 15.

  The probe shaft 4 is provided with a permanent magnet 72, and the housing 10 is provided with a coil 73. The coil 73 is connected to the current control device 71 and can pass a current through the coil. By energizing the coil 71, a force for driving the probe shaft 4 in the Z direction can be generated. An output from a sensor amplifier 14 that converts an output from an after-mentioned position sensor 23 into an electrical signal is connected to the current control device 71 in a branched manner so that positioning control between the housing 10 and the probe shaft 4 is possible. It has become.

  The measurement shaft 15 is supported by the XY table 28 using a guide 31 in the same direction as the probe shaft 4, that is, in the vertical direction (Z direction), and is driven by a ball screw 36 and a servo motor 29. The XY table 28 is guided so as to be movable in the X and Y directions with respect to a surface plate (not shown), and is positioned by a servo motor (not shown). A servo motor 29 that drives the measuring shaft 15 is connected to a servo amplifier 32, and the servo amplifier 32 is connected to a control system switching device 33. An encoder 30 is connected to the rotation shaft of the servo motor 29, and its output is connected to the position control compensation circuit 35. When the control system switching device 33 is connected to the position control system, the position of the measurement shaft 15 can be controlled. The control system switching device 33 is automatically controlled by a controller (not shown), and a measurement operation is performed according to the flowchart shown in FIG.

  Further, the interferometer 27 is fixed to the measurement axis 15, a reference mirror 26 is disposed above it, and the reference mirror 26 is fixed to the frame 25. With this configuration, the interferometer 27 can measure the distance between the mirror 6 and the mirror 26. A mounting table (not shown) for an object to be measured is provided in a lower portion of the frame 25, and the object to be measured 24 is fixed to the mounting table.

  The position sensor 23 is connected to the sensor amplifier 14 and converts the relative position between the probe shaft 4 and the housing 10 into an electrical signal. The sensor amplifier 14 is connected to a needle pressure control compensation circuit 34 and further connected to a control system switching device 33. When the control system switching device 33 is connected to the needle pressure control system, the servo motor is controlled so that the output of the sensor amplifier 14 becomes constant.

  Next, a measurement operation performed using the shape measuring apparatus configured as described above will be described with reference to the flowchart of FIG.

  First, the control system switching device 33 is set to the position control system, that is, the feedback control system is selected so that the position of the measurement shaft 15 is constant, and the safe position, that is, the probe is the most to be measured 24. The measuring shaft 15 is retracted in a direction away from the position (step S01).

  Then, the XY axis 28 is moved so as to be on the first measurement point (step S02).

  Next, the measurement shaft 15 is lowered to bring the probe into contact with the workpiece (step 04).

  When the probe comes into contact with the workpiece, the measurement axis is lowered until the probe position sensor 23 reaches a predetermined position (step 06).

  Here, when the ball 1 at the tip contacts the object to be measured and receives a reaction force, the probe shaft 4 is pushed up. When the probe shaft 4 is pushed up, z in the formula (1) increases to the plus side. Then, since the force generated by the magnetic circuit is weakened, the force with which the tip sphere 1 of the probe presses the object to be measured and the like gradually increases. This is the same effect as the spring element is there. Therefore, the output of the position sensor amplifier 14 represents the pressing force of the probe.

  The contact between the tip sphere of the probe and the object to be measured can be determined by monitoring the displacement measurement signal of the probe, that is, the signal of the sensor amplifier 14.

  Then, the control system changeover switch 33 is switched to the needle pressure control system to control the value of the position sensor 23 to be constant (step S06). As it is, the measurement area of the object to be measured is scanned (traced) using the XY axes, and at the same time, the position of the measurement axis is measured by a coordinate measuring device (not shown) (step S07).

  Further, the vertical direction of the probe is directly measured by an interferometer 27 that measures the distance between the mirror 6 and the reference mirror 26. When the entire measurement area is scanned, the control system switching device 33 is switched to the position control system again, the measurement axis is retracted to the safe position (step S08), and the measurement is terminated.

  The boil coilless motor control during the needle pressure control will be described with reference to FIG.

The basic idea of voice coil motor control is
1. The voice coil motor is controlled only while the measurement surface and the probe are separated, and a force is applied to the probe to positively return the probe to the measurement surface.

  2. The control equation for the voice coilless motor is F = −Kx−Cdx / dt (A equation).

  3. The time for returning the probe to the measurement surface is shortened by appropriately changing the K and C values in the formula A.

  4). Judgment as to whether or not the measurement surface is separated from the deviation of the needle pressure control.

  5. Once away from the measurement surface, a force is applied to the probe by Δt thereafter.

  In the following, description will be given in order.

  First, in step S06 (in FIG. 2), when the probe is switched to needle pressure control, it is detected by communication means (not shown) (S11), and parameters used for control are initialized (S12).

  Next, the current probe displacement x is acquired (S13). That is, the relative displacement between the housing 10 and the probe shaft 4 is acquired by the position sensor sensor 23.

  Next, the timer count t is compared with a predetermined threshold value Δt (S14). If the timer count t is larger than Δt, the process proceeds to S15, and if it is smaller, the process proceeds to S18. If the case classification in S14 is large, it means that the needle pressure control is satisfactorily applied. If it is small, it means that the needle pressure control is not working properly.

  In S15, the magnitude of the control deviation of the needle pressure control is compared with a preset Δe. In other words, if the result of comparison in S15 is large, it is assumed that the probe has been moved away from the measurement surface due to dust on the measurement surface. To do.

  When the timer count t is set to 0 in S17, the comparison result in S14 becomes smaller by Δt from the next turn of the control loop (S13 to S22) shown in FIG. 3, and the process proceeds to S18. In S18, the set spring constant K and the set viscosity constant C in the formula A are set, and then the timer count is advanced by one in S19.

  If the result of S15 is small, proceed to S16 and set the set spring constant K and the set viscosity coefficient C to zero.

  In S20, the generated force F of the voice coilless motor is calculated from K, C, x, dx / dt.

  A current is supplied to the voice coilless motor so that the calculated generated force is obtained (S21).

  Thereafter, it is confirmed whether or not the needle pressure control is finished (S22). If the needle pressure control is finished, the set spring constant and the set viscosity constants K and C are set to 0 and the process is finished.

  For example, assuming that the probe mass M is 10 g and the spring constant by the magnetic circuit is 0.001 mN / μm, the natural frequency f when the probe freely vibrates is 1 from sqrt (K / M) / 2 · / π. .6HZ. That is, when the probe is flipped up by dust on the surface of the measurement surface during scanning, 1 / 1.6 Hz / 2 = 0.3 s, which is half of one period of the natural frequency, is in a state where the probe is separated from the measurement surface. End up. Remote data cannot be used as measurement data. If the scanning speed is 10 mm / s, a section in which 10 mm / s × 0.3 s = 3 mm cannot be measured is formed. Furthermore, in the worst case, the control system may fail while the probe is away from the measurement surface, and the measurement may be stopped at that time.

  Therefore, as in this embodiment, the deviation during the needle pressure control is monitored, and if it exceeds the set threshold value Δe, it is determined that the measurement surface and the probe are separated. If the spring constant in the probe moving direction is artificially increased using a motor, the probe can be quickly returned to the measurement surface. For example, if the set spring constant set in S18 is set to 1 mN / μm, the natural vibration frequency f ′ of the probe becomes sqrt (K / M) / 2 / π to 50.3 Hz. Since the time to return to the measurement surface is considered to be half of the cycle, the time that was initially 0.3 S is reduced to 10 ms. In this case, the threshold value Δt in S14 may be set to a value longer than 10 ms, for example, 30 ms.

  Needless to say, if the set viscosity constant set in S18 is set to an appropriate value, the probe can smoothly land on the measurement surface. For example, if the set viscosity constant is set to about 4.42 N / (m / s), the damping ratio ζ becomes 0.7, and the probe that has just returned to the measurement surface can land smoothly without bouncing on the measurement surface.

  As described above, according to the present embodiment, a force generating element composed of the coil 73 and the permanent magnet 72 applies a force like a spring element or a force like a viscous element to the probe shaft 4. Can act according to the situation. As a result, even when the probe is flipped up by dust on the measurement surface, the time for the probe to leave the measurement surface can be shortened. Further, the probe that has returned to the measurement surface can be smoothly landed without splashing on the measurement surface.

It is a lineblock diagram showing a shape measuring device incorporating a contact type probe of an embodiment of the present invention partially broken. It is a flowchart explaining the measurement operation | movement of the shape measuring apparatus incorporating the contact-type probe of embodiment of this invention. It is a flowchart explaining control of the force generation element in the needle pressure operation | movement of the shape measuring apparatus incorporating the contact type probe of embodiment of this invention. It is a schematic diagram for demonstrating the contact-type probe of this embodiment. It is a schematic diagram for demonstrating the conventional contact type probe.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sphere 2 Probe tip 3 Spacer 4 Probe shaft 4a Probe shaft protrusion 5 Mirror fixing piece 6 Mirror 7 Yoke coupling jig 10 Housing 10a, 10b Stopper 10 Housing 11 Air bearing 12 Compressed air hole 13 Compressed pipe 14 Position sensor amplifier 15 Measurement axis 16 Second housing 17 Yoke 18 Permanent magnet 19 Iron core 20 Iron core holder 23 Position sensor 24 Work 25 Frame 26 Reference mirror 27 Interferometer 28 XY axis 29 Motor 30 Encoder 31 Guide 32 Motor amplifier 33 Control system switching device 34 Needle pressure control compensation circuit 35 Position Control Compensation Circuit 36 Ball Screw 71 Current Controller 72 Permanent Magnet 73 Coil 113 Permanent Magnet 114 Coil 115 Current Controller 121 Ball 122 Probe 123 Moving Unit 124 spring 131 position sensor 132 sensor amplifier

Claims (7)

It has a moving member that is fixed to the base member and can be moved three-dimensionally. It has a probe that can be moved in one direction at the tip of the moving member. In the shape measuring device that measures the position,
Having probe displacement measuring means for measuring the relative displacement between the probe and the base member;
Having a force generating means for generating a force acting on the probe with respect to the probe moving direction by being fixed to the base member;
Having control means for controlling the force generation means;
A shape measuring probe characterized in that the force applied to the probe by the force generating means and the control means is changed from information acquired from the probe displacement measuring means.   2. The probe according to claim 1, wherein the force applied to the probe by the force generating means is proportional to the relative displacement between the moving member and the probe.   2. The probe according to claim 1, wherein the force applied to the probe by the force generating means is proportional to the relative speed between the moving member and the probe.   4. The probe according to claim 2, wherein the proportional coefficient is switched.   5. The shape measuring probe according to claim 4, wherein the proportional coefficient is switched depending on a relative displacement value between the moving member and the probe.   5. The probe according to claim 4, wherein the proportionality coefficient is switched according to time.   4. The probe according to claim 2, wherein a force is applied to the probe by force generating means so that an attenuation ratio between the probe and the moving member is 0.7 or more.

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