JPH06194113A - Touch probe - Google Patents

Abstract

PURPOSE:To secure rigidity and allow a deep, narrow and hollow part to be measured with high sensitivity by forming a feeler into such a shape that the cross-sectional area of a part to come in contact with a measured object is smaller than the cross-sectional area of a part to come in contact with piezoelectric element mounting parts. CONSTITUTION:A vibrating horn 1 is made into a feeler of stepped bar shape through piezoelectric element mounting parts 1aa, 1ab and a flange 1d. The feeler is divided into a large diameter part 1b connected to the flange part 1d, and a small diameter part 1c. The tip of the part 1c is made into a contact 1f and used for a phase difference measuring circuit. The phase difference between the voltage of a connecting point 21 on the electrode 1eb side of a piezoelectric element 1ea and the voltage of a connecting point 13 on the resistance 11 side is monitored. When force disturbing vibration works at the time of vibrating the vibrating horn 1 ultrasonically at the mechanical resonance frequency, the phase difference between the voltage of a current flowing to the piezoelectric element 1ea and the voltage of the piezoelectric element 1ea is changed. This change is very sensitive and reacts even to slight external force. Measurement with high accuracy can be thus performed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a touch probe. More specifically, a probe for contact detection,
In particular, it relates to a touch probe used in a three-dimensional coordinate measuring machine.

[0002]

2. Description of the Related Art A touch probe used in a conventional measuring machine such as a coordinate measuring machine is provided with a piezoelectric element for converting a high frequency electric signal into ultrasonic vibration, as disclosed in Japanese Patent Laid-Open No. 4-140601. The ultrasonic vibrating horn is provided with a mounting portion and a feeler that is connected to the piezoelectric element mounting portion, and a step of the connecting portion is provided with an ultrasonic vibrating horn provided with a flange for holding the touch probe main body. A high-frequency electric signal is input to the piezoelectric element so that it almost matches the natural frequency, and the current between the electrodes of the piezoelectric element or the phase difference between the current and the voltage is monitored, which occurs at the moment when the feeler contacts the object to be measured. There is disclosed a touch probe that detects contact / separation between an object to be measured and a feeler by changing a current value or a phase difference between current and voltage.

[0003]

[Problems to be Solved by the Invention]

However, the touch probe disclosed in Japanese Patent Laid-Open No. 4-140601 discloses a touch probe and a feeler due to a change in the current or the phase difference between the current and the voltage when the feeler comes into contact with the feeler. Although it has the advantage that it can detect contact with and separation from, and has no directivity in the measuring force, it must be shortened to ensure rigidity because the feeler of the ultrasonic vibration horn is thin. If the length is increased, the rigidity is lacked and the risk of breakage is increased, which makes it impossible to measure a deep and narrow depression.

In view of the above problems, it is an object of the present invention to provide a touch probe capable of measuring an object to be measured having a deep and narrow recess.

[0006]

According to the present invention, there is provided a piezoelectric element mounting portion on which a piezoelectric element for converting a high frequency electric signal into ultrasonic vibration is mounted, one end of which is connected to the piezoelectric element mounting portion, and the other end of which is covered. A feeler having a contactor that comes into contact with an object to be measured, and a flange provided at a connecting portion between the piezoelectric element mounting portion and the feeler, and an ultrasonic vibration horn held in the touch probe main body by the flange, and An electrical characteristic value between the input means for inputting the high frequency electric signal to the piezoelectric element and the electrode of the piezoelectric element so that the mechanical natural frequency of the ultrasonic vibration horn and the frequency of the high frequency electric signal substantially match. And a touch detection unit that detects contact and separation between the object to be measured and the contactor by a change in an electrical characteristic value that occurs at the moment when the other end of the feeler comes into contact with the object to be measured. In the touch probe that, the shape of the feeler is a touch probe, wherein the direction of the cross-sectional area of the other end than the cross-sectional area of the one end is small.

A feeler includes a columnar portion having at least one step attached to the piezoelectric element mounting portion, and a contactor attached to the columnar portion and having a smaller cross-sectional area than the columnar portion. The feeler and the piezoelectric element mounting portion are formed of a contact portion, and the length of the columnar portion having at least one step is L, the length of the contact portion is M, and the piezoelectric element. When the length of the mounting portion is Q, C: sound velocity of a longitudinal wave in a substance forming the ultrasonic vibration horn, f: mechanical natural frequency of the ultrasonic vibration horn, n: positive integer, m: 0 Above integer r: If it is an integer above 0, a touch probe determined by L = C · 2n / 4f, M = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f), is preferable. is there.

The feeler has at least one tapered stepped columnar portion attached to the piezoelectric element mounting portion,
It is attached to the stepped columnar portion, is provided with the contact, and is formed from a contact portion smaller than the cross-sectional area of the stepped columnar portion, and the feeler and the piezoelectric element mounting portion are the stepped portions. When the length of at least one step of the columnar portion to the center of the taper is L, the length of the contact portion from the center of the taper is M, and the length of the piezoelectric element mounting portion is Q, C: ultrasonic wave Sound velocity of a longitudinal wave in a material forming a vibrating horn, f: mechanical natural frequency of an ultrasonic vibrating horn, n: a positive integer, m: an integer of 0 or more r: an integer of 0 or more, L = C A touch probe determined by 2n / 4f, M = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f), is preferable.

Furthermore, the feeler is formed in a taper shape in which the cross-sectional area gradually decreases from the one end attached to the piezoelectric element mounting portion toward the other end having the contactor, and When the length from one end to the other end is L and the length of the piezoelectric element mounting portion is Q, C: sound velocity of a longitudinal wave in a substance forming the ultrasonic vibration horn, f: of the ultrasonic vibration horn Mechanical natural frequency, m: integer of 0 or more r: integer of 0 or more, L = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f) Is.

[0010]

[Function] The section of the ultrasonic vibrating horn where the feeler comes into contact with the object to be measured has a small cross section, but the section where the feeler connects to the piezoelectric element mounting section is large and thick. The rigidity can be secured even if it is long. The feeler is connected to the piezoelectric element mounting portion at the flange, and the ultrasonic vibration horn is held at the touch probe main body by the flange.

Regarding the determination of the length of each part, when the feeler has a columnar part having at least one step and a contact part, the piezoelectric element mounting part, the length of the columnar part, and the contact part are determined. When the length is L = C · 2n / 4f, M = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f), the center of the flange and the position of each step become a vibration node. The lengths of the piezoelectric element mounting portion and each portion of the feeler are determined such that the tip of the feeler is antinode.

When the feeler has a tapered step, the lengths of the piezoelectric element mounting portion, the columnar portion, and the contact portion are L = C · 2n / 4f, M = C · (1 + 2m / 4f), and Q = C · (1 + 2r / 4f), the center of the flange and the position of the tapered step become a node of vibration, and the piezoelectric element mounting part and each part of the feeler are positioned so that the tip of the feeler is antinode. Is determined.

Further, when the feeler has a tapered shape whose cross-sectional area gradually decreases from one end toward the other end, the length of the feeler and the length of the piezoelectric element mounting portion are L = C. ( 1 + 2m / 4f), and Q = C · (1 + 2r / 4f), the center position of the flange becomes a node of vibration, and the length of the piezoelectric element mounting portion and the feeler are set so that the tip of the feeler becomes antinode. It is determined.

As described above, in the vibration mode, the flange serves as a node, and when there are multiple steps other than the flange, the node becomes a node regardless of whether the step is right-angled or tapered. When there is no step other than the flange, each appropriate position described above becomes a node. Then, the tip end portion of the feeler and the end surface of the piezoelectric element mounting portion on the side opposite to the flange form an antinode.

Then, the operation of ultrasonically vibrating the feeler of such an ultrasonic vibrating horn at a mechanical resonance frequency to detect contact will be described by taking the case of utilizing longitudinal vibration as an example. First, when the feeler resonates by using a piezoelectric element polarized in the axial direction, if the tip portion contacts the object to be measured, the vibration of the feeler is significantly hindered and the impedance of the piezoelectric element changes. This situation is represented by an electric circuit as follows. An equivalent circuit of a vibration system using a piezoelectric element is, as shown in FIG. 2, a coil Lm, a capacitor Cm,
It can be represented in a form in which a resistor Rm is connected in series and a capacitor Cd is connected in parallel. Lm at resonance
And Cm are series-resonated and canceled to form a circuit as shown in FIG. 3, and the impedance Z of the piezoelectric element is 1 / Z = j
It is expressed as ωCd + 1 / Rm. Where ω is the angular velocity of vibration. Since Rm has the property of becoming larger as the mechanical load such as the disturbance of vibration increases, the impedance Z increases when the tip sphere of the vibrating horn touches the object to be measured. Therefore, when the tip sphere touches the object to be measured, the current flowing through the piezoelectric element decreases.

When the applied voltage is E, the current flowing through the piezoelectric element is i = E (jωCd + 1 / Rm). This is because θ = arcta between the current i and the voltage E.
It indicates that there is a phase difference of n (ωCdRm). Here, when the resistance Rm increases, the phase angle θ increases. That is, when the feeler comes into contact with the object to be measured, the value of the current flowing through the piezoelectric element changes. Alternatively, the phase difference between the current and the voltage changes.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. As shown in the perspective view of FIG. 1 and the vertical sectional view of FIG. 1, the vibrating horn 1 is a feeler having a stepped rod shape with a piezoelectric element mounting portion 1a and a flange 1d. The feeler is divided into a large diameter portion 1b connected to the flange 1d and a small diameter portion 1c,
The tip of the portion 1c is a contactor 1f. Flange 1
d is fixed to the support member 2, and the support member 2 is held by a touch probe main body or a probe head (not shown).

The piezoelectric element mounting portion 1a is divided into a portion 1aa and a portion 1ab and is fixed with the piezoelectric element 1e sandwiched therebetween. The piezoelectric element 1e is of a laminated type and is polarized in the axial direction of the vibrating horn 1 as shown in FIG. 5, and the element 1ea is sandwiched between three electrode plates 1eb and 1ec. The electrode plate is short-circuited. When a high frequency voltage is applied between the electrode plates 1eb-1ec by a power supply device (not shown), the vibrating horn 1 ultrasonically vibrates in the axial direction. At this time, the applied frequency is substantially equal to the mechanical resonance frequency of the vibrating horn 1. Further, the length of each part of the vibrating horn 1 is such that C is the sound velocity f of a longitudinal wave in the substance forming the vibrating horn, and the mechanical natural frequency of the vibrating horn is
n = 0, _1, 2, 3, ..., N ₁ = 0, 1, 2,
3 ..., n ₂ = 0, 1, ₂ , 3, ...
The length of the piezoelectric element mounting portion 1a L, the length L ₂ of the length L ₁ and part 1c of the portion 1b of the feeler is L = C · (1 + 2n ) / 4f L 1 = C · 2n 1 / 4f L 2 = C・ It is decided by 2n ₂ / 4f.

When a steel material is used as the material of the vibration horn, the sound velocity C of the longitudinal wave transmitted through the steel material is C = 5200 m / s, and n = 0, n ₁ = 2, n ₂ = 0, f = 100 kHz.
Then, L = 13 mm, L ₁ = 52 mm, L ₂ =
It becomes 13 mm.

FIG. 6 shows the state of the vibration mode of the vibrating horn 1 at this time. A flange is provided so that the vibration amplitude is substantially 0 at the center of the flange, and the vibrating horn is used as a touch probe main body with this flange. Fix it. Since the fixing is performed at the vibration node of the vibrating horn 1 as described above, the resonance of the vibrating horn 1 is not hindered, and the influence of the vibration on the touch probe main body can be minimized. The step where the diameter changes is also provided at the place where the vibration amplitude becomes almost 0,
Resonance is not disturbed. As shown in FIG. 6, the vibration amplitude is almost 0 at the center of the flange, but when the flange is extremely thin, it may not be at the center of the flange.

In the vibrating state, the contact 1f of the vibrating horn 1
Since there is a vibration antinode at the position of and the amplitude is maximum, when this part comes into contact with the contacted object and is restrained, the vibration horn 1
Vibration is significantly hindered. When the vibration is disturbed, the electrical impedance of the piezoelectric element changes, and as a result, the current value flowing through the piezoelectric element changes. Alternatively, a slight change in the resonance frequency of the entire vibrating horn causes a change in the phase difference between the current and the voltage.

In this embodiment, the feeler is an example in which there are two parts having different diameters and one step. Even if there are two or more steps, the stepper is provided so as to come to the node position. do it. Further, the length of the tip portion 1c is as shown in FIG.
As shown in (b), when the node from resonance to node is λ, it may be λ / 2, that is, from node to antinode.

Next, the operation will be described. FIG. 7 is a block diagram of the first embodiment. Here, the phase difference measuring circuit will be described by taking an example using a single-layer piezoelectric element lea for simplification, but the phase difference measuring circuit is exactly the same even when the piezoelectric elements are laminated. The phase difference measuring circuit includes a piezoelectric element l.
The phase difference between the voltage at the connection point 21 on the electrode leb side of ea and the voltage at the connection point 13 on the resistance 11 side is monitored. When the vibration horn 1 is ultrasonically vibrated at the mechanical resonance frequency, if a force that impedes the vibration acts, the phase difference between the current flowing in the piezoelectric element lea and the voltage between the piezoelectric elements lea changes. This change is very sensitive and responds to even small external forces.

Since the output waveforms at the connection point 21 and the connection point 13 are sinusoidal waveforms, they are converted into square waves by the waveform shaping circuits 22 and 23 and are input to the clock and the clear of the flip-flop 24, respectively. Then, the output 102 appearing at the output terminal 24b of the flip-flop 24 (see FIG. 8 described later).
Is a pulse whose pulse width is the phase difference between the current flowing through the piezoelectric element lea and the voltage across the piezoelectric element lea. The output of the flip-flop 24 and the output of the clock oscillator 25 are A
It is input to the ND 26. The AND circuit 26 outputs the output 102 of the flip-flop 24 and the output 1 of the clock oscillator 25.
03 (see FIG. 8 described later) and outputs the result to the up counter 27. This counter 27 is AND
The reset terminal is connected to the waveform shaping circuit 23 while counting the output pulse of the circuit 26, and is reset at the rising edge of the pulse of the current output. The counted value is transferred to the latch circuit 2 by the digital comparator 29.
8 is compared with the set value stored in 8, and when the set value is exceeded, a touch signal is output from the digital comparator 29.

FIG. 8 shows the waveforms at the points in FIG. 7, part of which has been described above. Signal 100 is at point 22b in FIG. 7, signal 101 is at point 23b in FIG.
02 is at point 24b in FIG. 7, signal 103 is shown in FIG.
At point 25b, the signal 104 is point 26b in FIG.
It is in.

In the circuit of FIG. 7, the phase difference in the resonance state is smaller than the phase difference in the non-resonance state, and the phase difference becomes a minimum value at the resonance point. Therefore, the point at which the phase difference becomes the minimum value by changing the frequency input to the piezoelectric element is the resonance point. A value slightly larger than the count value of the up counter 27 at this time is used as a set value for the latch 28. This is to prevent the touch signal from being output even if an erroneous count occurs due to a response delay of the circuit or the like.

In this circuit, the phase difference in the non-resonant state is about 270 degrees, and in the resonant state is about 180 degrees.

Next, the second embodiment will be described with reference to FIGS.
Will be described. In this embodiment, the portion where the thickness of the diameter changes is tapered. The vibrating horn 31 is a feeler having a stepped rod shape with a piezoelectric element mounting portion 31a and a flange 31d. The feeler has a larger diameter portion 31b that connects to the flange 31d.
And a portion 31c having a small diameter, and a tapered portion 31g is formed between the portion 31b and the portion 31c.
Has a contact 1f. The flange 31d is fixed to the support member 32 by a fastening member 31h, and the support member 3
Reference numeral 2 is held by a touch probe main body or a probe head (not shown). Piezoelectric element mounting part 3 of vibration horn
1a is further divided into 31aa and 31ab.
It is fixed with e being sandwiched.

The state of the vibration mode of the vibrating horn is shown in FIG.
As shown in (b), the flange 31d, the portion 31b, and the tapered portion 31g each have one vibration node position, and the contact 31f is at the antinode position.

Since the operation of measuring the current or the phase difference between the current and the voltage is the same as that of the first embodiment, its explanation is omitted.

Next, a third embodiment will be described with reference to FIG. In this embodiment, a feeler 51b having a conical diameter that monotonically decreases is connected to the piezoelectric element mounting portion 51a via a flange 51d. A contactor 51f is provided at the tip of the feeler 51b. Feeler 51b
Since the flange 51d side is thick and the tip contactor 51f side is thin, the contact force can be kept small and the rigidity can be secured sufficiently large.

The state of the vibration mode of the vibrating horn is shown in FIG.
As shown in (b), the flange 51d is located at the vibration node, the contact 51f is located at the antinode position, and the conical portion 51b has two node positions.

Since the operation of measuring the current or the phase difference between the current and the voltage is the same as that of the first embodiment, its explanation is omitted.

In the first embodiment, the shape of the feeler is a cylindrical stepped rod. However, the shape of the feeler is not limited to this. For example, a stepped rod of a prism or a step of a combination of a cylinder and a prism is used. It may be a stick. Further, the sectional area of the feeler on the flange side may be made larger than the sectional area of the piezoelectric element mounting portion.

Although the resonance state due to the longitudinal vibration has been described in each of the embodiments, it goes without saying that other types of vibration, such as flexural vibration and torsional vibration, can be used.

[0036]

As described above, according to the present invention, the feeler of the ultrasonic vibration horn has a large and thick cross-sectional area at the portion connected to the piezoelectric element mounting portion and a small cross-sectional area at the portion in contact with the object to be measured. The thin and long feeler makes it possible to measure deep and narrow depressions because the measurement force is small and a non-directional contact is possible and the rigidity can be secured.

Since the ultrasonic vibration horn is held by the flange of the touch probe main body and the feeler is connected to the piezoelectric element mounting portion at the flange, the flange serves as an antinode of vibration and the touch probe main body and the feeler interfere with each other. It is possible to prevent the measurement accuracy from being lowered.

Regarding the determination of the length of each portion of the piezoelectric element mounting portion and the feeler, in the case of the one having the flange and the step, the piezoelectric element is mounted so that the position of each step becomes a node of vibration and the tip of the feeler is antinode. Since the lengths of the parts and the feeler parts are determined, and the bad resonance state that occurs when the flange and the step and the node do not coincide with each other can be avoided, the resonance state is good and therefore accurate measurement is possible.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment according to the present invention.

FIG. 2 is an equivalent circuit of the piezoelectric element according to the embodiment.

FIG. 3 is an equivalent circuit at the time of resonance of the piezoelectric element of one embodiment.

FIG. 4 is a vertical sectional view of one embodiment.

FIG. 5 is a sectional view illustrating a piezoelectric element.

FIG. 6 is a diagram showing an amplitude mode of the vibrating horn of one embodiment.

FIG. 7 is a block diagram showing a phase difference measuring circuit connected to a piezoelectric element according to an embodiment.

FIG. 8 is a diagram illustrating a waveform of a signal at each point of the circuit according to the embodiment.

FIG. 9 is a perspective view of a second embodiment according to the present invention.

FIG. 10 is a diagram showing an amplitude mode of the vibrating horn of the second embodiment.

FIG. 11 is a diagram showing an amplitude mode of a vibrating horn according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vibration horn 1a ... Piezoelectric element mounting part 1b, 1c ... Feeler part 1d ... Flange 1e ... Piezoelectric element 1f ... Contact element 2 ... Support member 10 ... -Oscillation circuit 11 ... Resistors 22, 23 ... Waveform rectification circuit 24 ... Flip-flop 25 ... Clock oscillator 26 ... AND circuit 27 ... Up counter 28 ... Latch circuit 29 ...・ Digital comparator

Claims (4)

[Claims] 1. A piezoelectric element mounting portion on which a piezoelectric element for converting a high-frequency electrical signal into ultrasonic vibration is mounted, and a contactor having one end connected to the piezoelectric element mounting portion and the other end contacting an object to be measured. A feeler having, and a flange provided at a connecting portion between the piezoelectric element mounting portion and the feeler,
The ultrasonic vibration horn held by the flange on the touch probe main body, the mechanical high frequency of the ultrasonic vibration horn, and the frequency of the high frequency electric signal substantially match, the high frequency electric signal to the piezoelectric element. Input means for inputting, and monitoring the electrical characteristic value between the electrodes of the piezoelectric element,
A touch probe having a touch detection unit that detects contact and separation between the object to be measured and the contactor by a change in an electrical characteristic value that occurs at the moment when the other end of the feeler comes into contact with the object to be measured. In the touch probe, the cross-sectional area of the other end is smaller than the cross-sectional area of the one end. 2. The feeler includes a columnar portion having at least one step attached to the piezoelectric element mounting portion, a columnar portion attached to the columnar portion, the contactor, and a disconnection of the columnar portion. The feeler and the piezoelectric element mounting portion formed of a contact portion smaller than the area have a length L of the columnar portion having at least one step, a length M of the contact portion, and the piezoelectric element. When the length of the element mounting portion is Q, C: the speed of sound of a longitudinal wave in the substance forming the ultrasonic vibration horn, f: the mechanical natural frequency of the ultrasonic vibration horn, n: a positive integer, m: An integer of 0 or more r: If an integer of 0 or more, L = C · 2n / 4f, M = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f) The touch probe according to claim 1. 3. The feeler is provided with at least one stepped columnar portion having a tapered shape that is attached to the piezoelectric element mounting portion, and is provided with the contactor while being attached to the stepped columnar portion. The feeler and the piezoelectric element mounting portion are formed by a contact portion smaller than the cross-sectional area of the columnar portion, and the feeler and the piezoelectric element mounting portion have a length L to the center of at least one taper of the stepped columnar portion, L When the length of the contact portion from the center is M and the length of the piezoelectric element mounting portion is Q, C: the speed of sound of a longitudinal wave in the substance forming the ultrasonic vibration horn, f: the machine of the ultrasonic vibration horn Natural frequency, n: positive integer, m: integer of 0 or more r: integer of 0 or more, L = C · 2n / 4f, M = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f), is determined by Touch probe as described. 4. The feeler is formed in a taper shape in which a cross-sectional area gradually decreases from the one end attached to the piezoelectric element mounting portion toward the other end having the contactor, and the feeler is formed from the one end. When the length to the other end is L and the length of the piezoelectric element mounting portion is Q, C: the speed of sound of a longitudinal wave in the substance forming the ultrasonic vibration horn, f: the mechanical strength of the ultrasonic vibration horn Natural frequency, m: integer of 0 or more r: integer of 0 or more, L = C · (1 + 2m / 4f), Q = C · (1 + 2r / 4f), The touch probe according to 1.