JPH0317513A - Displacement detector - Google Patents

Abstract

PURPOSE:To obtain a detector enabling power saving by detecting constantly whether a scale and a slider slide relatively or not and by lowering the frequency of a reference clock when sliding stops. CONSTITUTION:A slider 54 whereon grating corresponding to the grating of a scale 50 is arranged is provided so that it can slide relatively with the scale 50 in the direction of arrangement of the grating thereof. When the relative speed of movement of the scale 50 and the slider 54 is zero, that is, when the slider 54 can be regarded as standing still relatively, a speed detector 40 changes an output of a frequency switch 14 over to a low frequency and simultaneously changes a bias current of an operational amplifier in an analog circuit 20 over to a low value by a bias current switch 16. When the slider 54 starts to slide relatively again, the speed detector 40 detects the speed thereof and changes the frequency switch 14 over onto the source oscillator side while changing the bias current switch 16 over to a high bias current value.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an incremental type displacement detector, and in particular, when a scale and a slider are not sliding relative to each other, the distance between the scale and the slider is lower than when they are sliding. The present invention relates to an incremental type displacement detector that saves power by lowering the frequency of the reference clock or by simultaneously reducing the bias current of the analog circuit.

[Prior Art] Generally, when measuring the relative displacement of one member in length or angle of another member, a scale is fixed on one side and a slider is fixed on the other, and the displacement of the scale and the slider is measured with respect to the t-th point. Measurement devices include #% capacitance type displacement detectors (e.g., Japanese Patent Application No. 53-1.53588, etc.), optical displacement detectors (e.g., Japanese Patent Application No. 60-54022, etc.), and magnetic displacement detectors. (For example, Japanese Patent Application No. 52-62974) etc. are widely known, and are widely used as positioning devices for machine tools, optical instruments, precision measuring instruments, etc.

In many cases, these displacement detectors are not of the so-called absolute type, which has a mechanical absolute origin as a reference point, but rather have a reference point that is set arbitrarily, due to the ease of manufacturing the displacement detector. This is a so-called incremental method that counts the amount of relative displacement from .

Furthermore, even in precision measuring instruments such as digital calibers and digital indicators, an incremental method is used instead of an absolute method in many cases. Because these measuring instruments often need to be portable due to their uses, they are often powered by Z batteries. Therefore, in order to be able to use the displacement detector continuously for a long time, it is important to reduce the power consumption of the detection circuit.

[Problems to be solved by the invention] On the other hand, in the case of an incremental displacement detector,
Once the measurement reference point is set, it disappears when the power is turned off. Therefore, if it is necessary to measure a reference point once set as a common reference point, even if measurement is interrupted during that time, the displacement detection system will continue to perform measurements internally. The reference point must be saved and the power cannot be turned off. Therefore, it was necessary to devise ways to conserve power.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an incremental displacement detector that saves power.

[Means for Solving the Problems] Therefore, in the present invention, a scale having regularly arranged lattices, a lattice corresponding to the lattice of the scale, and a lattice corresponding to the lattice of the scale are arranged. A reference point that is arbitrarily set and includes a slider that is slidably disposed and a detection means that detects the amount of relative displacement between the scale and the slider based on the frequency of a reference clock built in a displacement detector. In an incremental type displacement detector that detects the amount of relative displacement between the scale and the slider described in 6if, means for detecting whether the scale and the slider are sliding relative to each other; Based on a signal from the detecting means, the frequency of the reference clock is switched to a lower frequency when the scale and the slider are not sliding relative to each other than when they are sliding; and a frequency switching means for switching to the original high frequency when the slider and the slider start sliding relative to each other. Further, the present invention provides that when the frequency switching means switches the frequency of the reference clock to a lower frequency, the bias current of the analog circuit used in the detection means is switched to a small current value, and
The present invention is characterized in that it includes bias current switching means for switching the bias current to the original high current value when switching the frequency of the reference clock to the original high frequency. Furthermore, in the case where the displacement detector is a capacitance type displacement detector, the capacitance type displacement detector is configured to detect relative displacement with the slider on the surface of the scale. A grid made up of a plurality of transmitting electrodes arranged in the direction of motion, and a receiving electrode in a strip-like relationship with the transmitting electrodes are provided, and the surface of the slider is arranged in the direction of the transmitting electrodes and the receiving electrodes. A grid consisting of a plurality of coupling electrodes is provided, which are arranged in a direction in which the slider moves, and which are opposed to each other. AC voltages having different phases are applied to each of the transmitting electrodes, and the receiving electrodes are connected to the receiving electrode. The present invention is characterized in that it is an electrostatic capacitor type displacement detector that detects the relative displacement between the scale and the mI slider by analyzing the phase of the measurement signal derived from the coupling electrode.

[Function] It always detects whether the scale and slider are sliding relative to each other, and when the scale and slider stop sliding relative to each other, the frequency of the reference clock is lowered, Alternatively, in conjunction with this, the bias current of the analog circuit used for the displacement detection means is reduced. In addition, when the scale and slider start sliding from a state where they have stopped relative to each other, the start of sliding is detected and the reference clock frequency is returned to the original high frequency, and the bias in the analog circuit is Return the current to its original high value.

[Example] As an example of the present invention, a capacitive displacement detector will be described in detail with reference to the drawings. However, the present invention is not limited thereby.

FIG. 5 shows the electrode structure of a capacitive displacement detector. The slider 54 is provided with transmitting electrodes 60 having a wt number at equal intervals and a band-shaped receiving electrode 62 that is parallel to the transmitting electrodes, and the scale 50 facing the slider 54 is provided with transmitting electrodes 60 and receiving electrodes. Coupling electrodes 64 and ground electrodes 66, which are arranged facing each other across the electrode 62, are arranged alternately and regularly along the sliding direction.

AC voltages shifted one after another by the same amount of phase are applied to each transmitting electrode 60 . Charges corresponding to the phase of the applied AC voltage are induced in the capacitance formed by each transmitting electrode 60 and the coupling electrode 64. As a result, a composite charge consisting of charges that behave in accordance with each phase is induced in the coupling electrode 64. A signal based on these combined charges is transmitted to the receiving electrode 62 via the coupling electrode 64 and received. The amount of relative displacement between the scale 50 and the slider 54 is detected from the phase amount shifted with respect to the reference phase of the received signal. FIG. 1 is a block diagram of a circuit of a capacitive displacement detector according to an embodiment of the present invention. shows. The detector circuit mainly includes a source oscillator 10, a frequency divider l2, a frequency switch 14, a bias current switch 16, an analog circuit 20, and a digital circuit 30.
and a speed detection circuit 40, and is connected to the transmitting electrode 6o and the receiving electrode 62. The detailed configurations of the analog circuit 2o and the digital circuit 30 are shown in FIGS. 2 and 3, respectively.

The source oscillation MIO is a reference clock of the displacement detector, and has a frequency of f. The timing of all signal processing of the displacement detector and the generation of necessary signals are performed with reference to this reference clock. The frequency f of the source oscillator 10 is determined by the frequency divider 1
2 to f/n. The output of the source oscillator 10 and the output of the frequency divider l2 are each connected to a switching terminal in a frequency switching l4. Frequency switching l4
The output of is connected to a digital circuit 30. The detection signal detected from the receiving electrode 62 is waveform-shaped in the analog circuit 20 and then input to the digital circuit 30 . Further, the digital circuit 3o generates a drive signal corresponding to the AC voltage applied to the transmitting electrode 60. These drive signals are phase-shifted by a predetermined value and applied to the corresponding transmitting electrodes 60. The digital circuit 30 also sends a signal to the speed detection circuit 40 for monitoring the relative movement speed between the scale 50 and the slider 54.

Speed detection is performed by constantly monitoring the period of the output signal waveform of the analog circuit 20.

As shown in FIG. 3, the digital circuit 30 mainly includes a comparison oscillator 32, a phase comparator 34, a counter 36, and a transmitting electrode drive signal generator 38.

The comparison oscillator 32 receives the output signal (second
This provides a reference waveform for detecting the phase change in Figure 21(d)). The frequency is the same as the frequency when the slider 54 is at rest. When the slider 54 moves, the phase of the output signal 21(d) changes depending on its speed. The output signal 21(d) is compared in phase with the reference phase of the waveform of the comparison oscillator 32 in a phase comparison 34. The results are counted by a counter 36. The amount of phase shift, including positive and negative, is performed every cycle of the waveform of comparison oscillator 32, and the total count value of these phase comparisons represents the amount of displacement of slider 54.

The transmission electrode drive signal creation section 38 creates a drive signal to be applied to the transmission electrode 60. In principle, as mentioned above, it is a signal waveform of a pulse train as shown in an AC current whose phase is shifted by the same phase, and this combined waveform has a predetermined phase (
For example, the signal is shifted by 45 degrees) and applied to each transmitting electrode 60. The signal waveform shown in FIG. 4(a) is a signal generated from the reference clock output from the frequency switching 14, and is synchronously rectified in synchronization with a synchronization signal (not shown) generated from the reference clock. Then, Figure 4 (b
) is generated as a waveform signal.

The signal waveform in FIG. 4(a) is such that the displacement amount of the slider 54 and the displacement amount analyzed from the signal waveform 21(a) are accurate by canceling edge effects caused by the electrode shape of the transmitting electrode 60. It should be designed to be well proportioned. The reason why the drive signal applied to the transmitting electrode 60 is not a raw AC voltage waveform but a pulse train as shown in FIG. 4(a) is because the basic clock pulse based on the source oscillator 10 This is to enable digital generation and processing of necessary signals in the capacitive displacement detector.

As shown in FIG. 2, the analog circuit 20 mainly includes a demodulation circuit 22, a filter 24, and a waveform shaping 26.

The demodulation circuit 22 demodulates the signal waveform 21(a) detected from the receiving electrode 62 into a signal waveform 21(b). Demodulation in the demodulation circuit 22 is performed by synchronous rectification in synchronization with a synchronization signal (not shown) generated from a reference clock.

Here, the signal waveform 21(a) is a composite signal generated by shifting the pulse trains shown in FIG. 4(a) by a predetermined phase amount, and adding these pulse trains with a predetermined weight over each phase. It is. The predetermined weight is
This is an amount proportional to the value of the capacitance formed between the transmitting electrode 60 and the coupling electrode 64 corresponding to that phase.

After passing through the filter 24, the signal waveform 21(b) has its high frequency components removed and becomes a signal voltage 21(C), and then undergoes waveform shaping 2.
6 gives a signal waveform 21(d). The signal waveform 21(d) is then input to the digital circuit 30.

The speed detection circuit 40 includes a scale 50 and a slider 5.
When the relative movement speed with respect to 4 is zero, that is, the slider 54 can be considered to be relatively stationary, the frequency switching l
At the same time as the output of 4 is switched to a lower frequency f, the bias current of the operational amplifier in the analog circuit 20 is switched to a lower value by the bias current switch 16. Also,
When the slider 54 starts relative sliding again, the speed detection circuit 40 detects the speed and switches the frequency switch 14 to the frequency f ffll+ and the bias current switch 16 to the high bias current value OII1.

As described above, a characteristic feature of the present invention is that the frequency of the reference clock and the bias current value of the analog circuit are switched by detecting whether or not the slider 54 is stationary relative to the scale 50. The digital circuit 30 of this embodiment is composed of CMOS, and it is well known that the current consumption of CMOS decreases when the driving frequency is lowered. On the other hand, when the frequency of the reference clock is lowered, the period of the waveform of the drive signal applied to the transmitting electrode 60 also becomes longer (FIG. 4(a)). As a result, the receiving electrode 62
Similarly, the period of the detected signal becomes longer. and,
As a general property of operational amplifiers, when the frequency of the signal to be handled becomes lower, faithful amplification characteristics are exhibited even when a lower bias current is passed. Sometimes, when the target is stationary, there is no problem even if it is lowered. In this manner, by switching the frequency of the reference clock to a lower frequency when the slider 54 is relatively stationary, the digital circuit 30 and the analog circuit 2
By suppressing the current consumption at zero, the current consumption of the power source of the displacement detector can be significantly reduced.

Note that when the slider 54 begins to slide, it must return to its original frequency and bias current, but if you confirm that the acceleration of the slide is below a certain level, the slider 54 It is possible to restore the large amount of displacement without miscounting.

Although a capacitive displacement detector has been described as an embodiment of the present invention, the present invention is not limited to this, but can also be applied to photoelectric or magnetic incremental displacement detectors.

Further, it goes without saying that the displacement detector according to the present invention includes a displacement meter that detects not only linear displacement but also rotational displacement.

[Effects] As described above, according to the present invention, it is possible to provide an incremental displacement detector that saves power.

Since portability is required, it is possible to use an incremental displacement detector driven by a battery for a long period of time. In addition, in the displacement detection device with reduced current consumption according to the present invention, it is even more convenient to back up the current of the displacement detector with a secondary battery such as a supercapacitor when the displacement detector is at rest. This effectively shows the absolute displacement detector and the electrode structure of the detector.

50...Scale, 54...Slider 60,.
- Transmission electrode, 62-...Reception electrode, 64...Coupling electrode.

FIG. 1 shows a block diagram of a circuit of a capacitive displacement detector according to an embodiment of the present invention. FIG. 2 shows a block diagram of the analog circuit 20 in FIG. 1 and signal waveforms at each part. FIG. 3 shows the digital circuit 30 in FIG.
The block diagram is shown below. FIG. 4 shows a part (a) of the drive signal fε to the transmitting electrode 60 in FIG. 1, and a corresponding signal waveform (b) when the drive signal is demodulated.

Claims (3)

[Claims] (1) a scale having regularly arranged gratings; a slider having gratings corresponding to the gratings of the scale arranged so as to be slidable relative to the scale in the direction in which the gratings are arranged; a detection means for detecting the relative displacement amount between the scale and the slider based on the frequency of a reference clock built into the displacement detector, and detecting the relative displacement amount between the scale and the slider from an arbitrarily set reference point. In an incremental type displacement detector for detecting, the reference clock is determined based on a means for detecting whether the scale and the slider are sliding relative to each other, and a signal from the detecting means. when the scale and the slider are not sliding relative to each other, the frequency is switched to a lower frequency than when the scale and the slider are sliding relative to each other, and the scale and the slider have started sliding relative to each other. Sometimes switching back to a higher frequency,
A displacement detector comprising frequency switching means. (2) In claim (1), when the frequency switching means switches the frequency of the reference clock to a lower frequency, the bias current of the analog circuit used in the detection means is switched to a small current value, and the 2. The displacement detector according to claim 1, further comprising bias current switching means for switching the bias current to the original high current value when switching the frequency of the reference clock to the original high frequency. (3) In claim (1) or claim (2), the displacement detector described in claim (1) or claim (2) is a capacitive displacement detector, and the capacitance The type displacement detector is provided with a grid on the surface of the scale, consisting of a plurality of transmitting electrodes arranged in the direction of relative movement with the slider, and a receiving electrode in a band-like relationship with the transmitting electrodes. a lattice consisting of a plurality of coupling electrodes is provided on the surface of the slider, facing across the transmitting electrode and the receiving electrode, and arranged in the moving direction of the slider, each transmitting electrode having: , a capacitive displacement detector to which alternating current voltages having different phases are sequentially applied, and the receiving electrode analyzes the phase of the measurement signal derived from the coupling electrode to detect the relative displacement between the scale and the slider. The displacement detector according to claim (1) or claim (2), characterized in that: