JPH045121B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to touch signal detection circuits, particularly when a touch signal probe including a directional detection element for each axis is used in a coordinate measuring machine or the like. The present invention relates to an improved touch signal detection circuit for synthesizing probe signals to obtain a stable touch signal in all directions.

[Prior Art] In three-dimensional coordinate measuring machines and other devices, it is desired to accurately detect a touch signal when a touch signal probe contacts an object to be measured.

As is well known, a coordinate measuring machine has a structure that reads and stores the coordinates of each axis scale when the probe contacts the object to be measured, and calculates each measurement point of the object based on this. If there are variations in the touch signals output when the probe and the object to be measured come into contact, this will directly appear as an error. Therefore, the touch signal must be output with a substantially constant minute delay regardless of various measurement conditions or the contact state between the probe and the object to be measured.

Conventional general touch signal probes include:
The inclination or movement of the stylus that occurs when it makes contact with the object to be measured is used to connect and separate the contacts, and to obtain electrical on/off signals directly from the contacts, but touch signal probes using this type of contact method However, the contact state of the contacts is unstable and noise is easily picked up, and since the signal detection is directional, it is not always possible to detect touch signals with high precision.

In recent years, touch signal probes that use other electrical detection elements instead of conventional contacts have been put into practical use, significantly improving the reliability of touch signal detection and enabling high-precision detection. There is.

As this type of detection element, for example, a piezoelectric element is known, and the force generated when the stylus of the probe contacts the object to be measured is used to apply compressive force (tension) to the piezoelectric element, which is generated at this time. A touch signal is obtained using a piezoelectric voltage.

In addition, devices that utilize the piezoelectric effect of piezoelectric elements as a piezoelectric effect due to shear force, which is different from the compressive force (tension), have recently attracted attention, and touch signal probes are used to generate signals using such shear force. It has been found that it is significantly advantageous to obtain

According to the piezoelectric element that uses the piezoelectric effect caused by the shearing force described above, the output characteristics of the piezoelectric element are directional as shown in Fig. output, and exhibits low sensitivity characteristics in the direction orthogonal to this.

Therefore, when using the shear force of such a piezoelectric element, by arranging piezoelectric elements with different polarization directions for each axis and combining their outputs, the probe can be contacted in all directions. shall be a detectable circuit.

However, since the probe signal itself has polarity when combining such multi-axis outputs using a conventional simple adder circuit, depending on the direction of probe movement, the addition of positive and negative signals cancels each other out, resulting in a combined output. There were cases where it was not possible.

Therefore, there is an idea of processing multi-axis output synthesis having such polarity using a square root circuit.

However, such a circuit requires the use of a squaring circuit with a poor signal-to-noise ratio, and as is well known, when the processing voltage of a typical squaring circuit is low, its accuracy deteriorates significantly and external noise is mixed in. Therefore, it has been difficult to apply it to circuits that require highly accurate signal processing, such as touch signal detection circuits.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to synthesize a plurality of probe signals with polarity and to solve the problem in response to contact of the probe in any direction. Another object of the present invention is to provide an improved touch signal detection circuit that can obtain stable and highly accurate touch signals.

[Means for Solving the Problems] In order to achieve the above object, the present invention filters each probe signal and then sample-holds it to determine and fix a reference value, and compares this reference value with each probe signal. A change absolute value detection circuit outputs a change absolute value signal indicating the absolute value of the difference between each probe signal with respect to a reference value, and a change absolute value detection circuit outputs a change absolute value signal indicating the absolute value of the difference between each probe signal with respect to a reference value. It has a means for fixing/releasing the previous reference value by outputting it as a signal and controlling the amount of delay due to filtering in the change absolute value detection circuit, and synthesizes each change absolute value signal and outputs it to all of the probes. It is characterized by detecting a stable touch signal with respect to touch in the direction.

Therefore, according to the present invention, a highly accurate touch signal can be provided without requiring a conventional low-accuracy squaring circuit in the processing circuit.

[Embodiments] Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 3 shows a schematic configuration of a three-dimensional coordinate measuring machine including a touch signal detection circuit to which the present invention is applied. Stylus 1 that can be moved freely
2 is provided, and this stylus 12 is connected to the object to be measured 1
4, and the scale coordinates of each axis are read by the touch signal at this time.

In the probe 10, an X-axis piezoelectric element 16, a Y-axis piezoelectric element 18, and a Z-axis piezoelectric element 20 are sequentially stacked and arranged, and the movement of the stylus 12 is electrically controlled by each piezoelectric element 16 to 20. The touch signal is detected and supplied to the touch signal detection circuit 22. Each piezoelectric element 16-20 in this embodiment uses a piezoelectric effect due to its shearing force, and as a result, has good detection sensitivity. Generally, a piezoelectric element exhibits a highly sensitive detection characteristic for shear force along the polarization direction, but the detection sensitivity is significantly reduced in a direction perpendicular to this direction.

Therefore, in the touch signal detection circuit 22, the outputs of the piezoelectric elements 16 to 20 arranged along their respective unique detection directions are combined, and the movement of the stylus 12 in all directions is controlled with substantially the same delay characteristics. calculate.

The touch signal that is the output of the touch signal detection circuit 22 is supplied to the coordinate reading circuit 24, and the probe 1
X scale 26 indicating the position along each axis of 0, Y
The coordinate values of the scale 28 and the Z scale 30 at the time of contact are read and stored in the register 32.

Then, the output of the register 32 is sent to the computer 3.
4 and is used for predetermined calculations, and the coordinates of the measurement point can be displayed on the display 36 if necessary.

In the present invention, the touch signal detection circuit 2
2, the probe signals obtained by the piezoelectric elements 16 to 20 are shaped into desired touch signals, and the configuration of this touch signal detection circuit with respect to the XY axes is shown in FIG.

The piezoelectric element, for example the X-axis piezoelectric element 16, can be considered as a highly sensitive, high impedance capacitor element, and its output is impedance-converted by the preamplifier 40 and output as a probe signal 100.

That is, this probe signal 100 contains a low frequency drift based on the characteristics of the piezoelectric element 16 or the preamplifier 40, generally a drift component of about 1/100 Hz, and therefore it is difficult to calculate the difference from the fixed reference value. Even if an attempt is made to obtain the change output at the time of contact, the 0 level will fluctuate, so the change absolute value output will contain a large error.

In this regard, in the present invention, the probe signal 10
There is an advantage that when the absolute value of the change is obtained by forming the reference value for the difference calculation using 0 itself, the low frequency drift component is also removed at the same time.

A characteristic feature of the present invention is that the probe signal 100 is converted into a change absolute value 106 by the change absolute value detection circuit 38, that is, the probe signal 100 has a polarity as described above. Even if an output cannot be obtained by simply adding these probe signals 100 by adding signals of positive and negative polarity, in the present invention, the absolute value of the change is extracted by the detection circuit 38.

In addition, in the embodiment shown in FIG. 1, after each of the plurality of probe signals obtained from each axis is converted into an absolute value, only the maximum value of the input probe signals is picked up as a touch signal. In the figure, an OR circuit 52 is provided.

Although only two axes, the X and Y axes, are shown in Figure 1, it is of course possible to detect the maximum value of the outputs of the piezoelectric elements in all three axes shown in Figure 3 using an OR circuit if necessary. suitable.

In FIG. 1, a change absolute value detection circuit 54 similar to that for the X axis is provided on the Y axis, and the outputs of the respective detection circuits 38 and 54 on both axes are sent to an OR circuit 5.
2 is supplied.

FIG. 4 shows the directivity characteristics of each piezoelectric element 16 and 18 with respect to the X and Y axes in FIG. The directional characteristics also have high sensitivity along the X-axis, while the Y piezoelectric element 18 has high-sensitivity directional characteristics along the Y-axis.

In the embodiment shown in FIG. 1, the contact of the probe along the XY plane is made into a touch signal by taking out the larger absolute value of both piezoelectric elements 16 and 18, and thereby mutually mutually in both axial directions. A complementary composite touch signal is obtained, and as is clear from the composite characteristics shown by the thick solid line in FIG. 4, it is understood that the directivity is sufficiently improved compared to each individual piezoelectric element.

In FIG. 1, the configuration of the change absolute value detection circuit 38 regarding the X-axis will be described below.

In the illustrated embodiment, the absolute value of change is obtained by calculating the difference between the probe signal 100 and a reference value based on the probe signal 100 itself, and is output to the OR circuit 52 as the absolute value of change 106. . In this embodiment, the low frequency drift component included in the probe signal 100 is also removed at the same time, making it possible to obtain an extremely high quality signal as the absolute value of change 106.

The configuration of the embodiment shown in FIG. 1 will be explained below along with its operation with reference to the waveform diagram of each part shown in FIG. 2.

The probe signal 100 in FIG. 2 exhibits a steep rising characteristic at time t ₁ when the probe comes into contact with the object to be measured, and at time t ₄ when the probe leaves the object to be measured again, the signal value falls. Show characteristics.

Note that in the figure, a fine fluctuation component is shown in the signal 100 in order to clearly show that the probe signal 100 includes a low frequency drift component, but in reality, this fluctuation component is not as shown in the diagram. It changes at a much larger wavelength, so it will never have such a short cycle.

A characteristic feature of this embodiment is that the probe signal 100 is converted into a reference value 104 through a low-pass filter 42 and a sample hold circuit 44, and this reference value 104 and the probe signal 100 are converted to a difference calculator. 46, the difference is calculated and output as the absolute value of change 106, which is a feature of the present invention.

The low-pass filter 42 has a cut-off frequency on the low side, for example, 1, in order to pass the low-frequency drift component as it is and to give a predetermined delay to the change at the time of contact that has a steep rise.
Hz, and considering the characteristics of the low-pass filter, the output 102 corresponds to the chain line 102' in FIG.
The output will be as shown in . However, in this embodiment, the low-pass filter 42 can be switched not only to the cutoff frequency on the low side but also to the cutoff frequency on the high side, for example, a high frequency characteristic of about 1 KHz. In this case, the low-pass filter 42 does not provide any delay characteristics to the high frequency change at the time of contact, and functions simply as an amplifier with an amplification degree of 1.
The probe signal 100 will be output as is.

In this embodiment, as will be described later, a touch signal is output at time _t2 delayed by Δt from probe contact start time _t1 , and the low-pass filter 42 at this time is switched to the high frequency side. As shown by the solid line in FIG. 2, the low-pass filter output 102 has the same waveform as the probe signal 100 after time _t2 .

In a normal state, the sample hold circuit 44 outputs the low-pass filter output 102 as it is, and it is clear that this reference value 104 is the same as the probe signal 100 when the probe and the object to be measured are not in contact.

Therefore, the difference calculator 46 does not output any signal when the probe is not in contact with the probe, and from this, even if there is a low frequency drift component, it is possible to reliably remove the 0 level fluctuation caused by the low frequency drift component. Become.

On the other hand, when the probe comes into contact with the object to be measured, as described above, this high frequency changing component is delayed by the low pass filter 42, and as a result, the reference value 10, which is the output of the sample hold circuit 44, is delayed.
4 has a value different from that of the probe signal 100. Therefore, the difference calculator 46 outputs the absolute value of change 106.

The absolute value of this change 106 is the probe signal 100
Regardless of the positive or negative polarity of the probe signal 100, the signal is always output as an absolute value by calculating the difference between the probe signal 100 and the reference value 104, thereby eliminating the need for an unstable squaring circuit like the conventional one. It is understood that absolute value conversion can be easily performed without having to do so.

The above absolute value conversion is performed on the X-axis, but in FIG.
6Y is output, and the absolute value of both these changes is 106,
106Y is supplied to the OR circuit 52 as described above, and the larger value is output as the composite signal 110, as shown by the characteristics in FIG.

Then, the composite signal 110, which is the absolute value of the maximum change, is compared with the threshold value Vth in the next comparator 48, and the threshold value Vth
is a predetermined constant value, and as shown in Figure 2, the absolute value of the change is 106 (the composite signal when it is larger than 106Y), which is the threshold value.
When Vth is exceeded, that is, at time t ₂ after Δt has elapsed from the start of touch t ₁ , the touch signal 108 is output.

When the output of the low-pass filter is a virtual value 102', the absolute value of change 106, which is the output of the difference calculator 46, is also a virtual value 10, which is indicated by the chain line in FIG.
6', but in reality, as described above, the characteristics of the low-pass filter 42 are switched, and more importantly, the reference value 104 of the sample-and-hold circuit 44 is fixed at sampling time _t2 , so After _2, the absolute value of change is 106
indicates a waveform as shown by a solid line.

This absolute value of change 106 is determined by the contact of the stylus 12 of the probe 10 with the object to be measured 14 and the piezoelectric element 1.
In this embodiment, the absolute value of the piezoelectric voltage based on the shear force obtained from 6 is approximately the same as the probe signal 100 while the stylus 12 is in contact with the object to be measured 14 due to sampling by the sample hold circuit 44. The waveforms are similar, and for this reason, the time t ₃ is just Δt _' immediately before the time t 3 , that is, the time t ₄ when the stylus 12 leaves the object 14.
The touch signal 108 crosses the threshold value Vth again at this stage, and the touch signal 108 returns to the 0 level.

In this embodiment, at time _t2 when the touch signal 108 is output, the touch signal 108 is supplied as a trigger signal to the controller 50, and the controller 50 puts the sample-and-hold circuit 44 into the sampling state at this point. ,
The absolute value of the change in the fall of the touch signal 108 is 10
It depends only on the waveform of 6.

Further, at time t ₂ , the controller 50 simultaneously switches the characteristics of the low-pass filter 42 to the high frequency side, making its output 106 almost the same as the probe signal 100 . As is clear from the low-pass filter output 102 in FIG. 2, this characteristic switching is possible because if the low-frequency characteristic remains unchanged, the low-pass filter output 102 will have a sufficiently long delay time even when the probe stylus leaves the object to be measured. In some cases, a delay time of several seconds is given to the probe signal 100, and in such a case, an unnecessary false touch signal is generated by the delayed low-pass filter output 102 even after the time _t3 . In order to prevent such a situation, the characteristics of the low-pass filter 42 are switched to the high frequency side together with the sample hold.

Therefore, according to this embodiment, the above-mentioned false touch signal is not output.

As described above, according to this embodiment, the absolute value of change 106 is output from the difference calculator 46, and this is further compared with the desired threshold value by the comparator 48, thereby generating the probe signal 100. It is possible to obtain an extremely stable touch signal 108 with improved directivity by removing low frequency drift contained in the signal.

After time _t3 when the touch signal 108 disappears, the controller 50 switches the low-pass filter 4
2 and the sample hold circuit 44, the characteristics of the former are switched to the lower frequency side, and the sample hold is canceled.

As described above, according to the embodiment shown in FIG. 1, after the probe signal is converted into an absolute value, the maximum value among the plurality of signals is extracted and the directivity of each individual probe signal is improved to improve the probe signal. Touches in all directions can be detected.

FIG. 5 shows a second embodiment of the touch signal detection circuit according to the present invention, and the same members as those in FIG.

The characteristic feature of the second embodiment is that after the XY probe signal 100 is converted into an absolute value, these two signals are simply added by the adder 56, and both inputs have already been converted into absolute values. Since the polarity has been removed, a composite characteristic as shown in FIG. 6 can be obtained by simple addition.

As is clear from FIG. 6, it is understood that the directivity of the added composite characteristics is significantly improved compared to the respective directivity characteristics of the X and Y piezoelectric elements 16 and 18, and the output Since the value itself can be made sufficiently large, it greatly contributes to improving detection sensitivity.

In each of the embodiments described above, a low-pass filter, a sample hold circuit, and a difference calculator are used to obtain the absolute value of the change, but in the present invention, such a change in the absolute value of the probe signal is This can be done with a circuit configuration, and FIGS. 7 and 8 show other embodiments of the absolute value conversion circuit.

FIG. 7 includes a variation absolute value detection circuit 58 that removes the polarity of the DC component by AC coupling, for example,
The probe signal 100 of the axial piezoelectric element 16 has its DC component removed by an AC coupling circuit consisting of a capacitor 60, a resistor 62, and an amplifier 64, and then is converted into an absolute value by an absolute value circuit 65 consisting of a combination of a well-known operational amplifier and a rectifier. It becomes possible to perform value conversion.

In FIG. 8, absolute value conversion is performed by a change absolute value detection circuit 66 including a charge amplifier.The output of the piezoelectric element 16 is used as a generated charge signal, and this charge is charged to a capacitor 68. An output proportional to the generated charge is output from the amplifier 70 via the high-pass filter 72, and the DC component is removed and the absolute value detection circuit 7
3, it is possible to perform absolute value conversion.

As described above, according to the present invention, a touch signal with extremely high sensitivity can be detected by converting the absolute value of a plurality of probe signals in different axial directions with directivity and polarity and synthesizing them. Although the above-mentioned probe signal is shown as a signal using the shear force of a piezoelectric element in the example, the present invention also applies to directional and polar probe signals obtained from other arbitrary elements. The invention is applicable.

[Effects of the Invention] As explained above, according to the present invention, a touch signal that is stable in all directions can be detected by combining at least two or more probe signals that have directionality and polarity. In order to do this, the probe signal is first converted into a variation absolute value signal and then synthesized, so it is possible to obtain a touch signal with high precision without errors in the processing circuit compared to the conventional method.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a preferred embodiment of the touch signal detection circuit according to the present invention, Fig. 2 is a waveform diagram of each part of Fig. 1, and Fig. 3 is a three-dimensional measurement of the touch signal detection circuit according to the present invention. 4 is a composite characteristic diagram obtained by extracting the maximum value in the embodiment of FIG. 1, and FIG. 5 is a second preferred embodiment of the touch signal detection circuit according to the present invention. A circuit diagram showing an example, FIG. 6 is a composite characteristic diagram by the addition action in the second embodiment, and FIGS. 7 and 8 are main part circuit diagrams showing other embodiments of the absolute value of change detection circuit according to the present invention,
FIG. 9 is a characteristic diagram of a piezoelectric element using shear force. 10... Probe, 14... Measured object, 16,
18, 20... Piezoelectric element, 22... Touch signal detection circuit, 38, 54, 58, 66... Change absolute value detection circuit, 40... Preamplifier, 42... Low pass filter, 44... Sample hold circuit,
46... Difference calculator, 48... Comparator, 50... Controller, 52... OR circuit, 56... Adder, 100... Probe signal, 102... Low pass filter output, 104... Reference value, 106 ……
Absolute value of change, 108...Touch signal, 110...
...Synthetic signal.

Claims (1)

[Scope of Claims] 1. A touch signal detection circuit that detects a touch signal by synthesizing a plurality of polarized probe signals detected from a touch signal probe corresponding to different axial directions due to contact with an object to be measured, A change in which each probe signal is sampled and held after filtering to obtain a reference value, and this reference value is compared with each probe signal to output a change absolute value signal indicating the absolute value of the difference of each probe signal with respect to the reference value. A minute absolute value detection circuit compares the composite value of the change absolute value signal with a predetermined threshold value and outputs it as a touch signal,
means for fixing/releasing the reference value by controlling the amount of delay due to filtering in the change absolute value detection circuit; A touch signal detection circuit characterized by detecting a stable touch signal.