JPS5914165B2 - Digital length measuring device signal detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection circuit for a digital length measuring device, and more particularly to an improved signal detection circuit that can obtain highly accurate digital signals by dividing a detection signal into multiple parts.

A digital length measuring device that electrically detects the length of the object to be measured and displays it digitally based on this detection signal is well known, and is attached to a digital micrometer, digital caliper, or machine tool to determine the processing position. Alternatively, it is widely used in digital scales for measuring coordinates, etc.

The detectors used in digital length measuring instruments are photoelectric, electromagnetic,
There are various types including a magnetic type detector, and FIG. 1 shows a schematic configuration of a photoelectric type detector. In the figure, lattice stripes 10a consisting of light transmitting parts and non-light transmitting parts are arranged on the surface of a main scale 10, and an index scale 12 is arranged near the main scale 10. The surface of the index scale 12 is also provided with lattice stripes 12a and 12b similar to the main scale 10, and both lattice stripes 1
2a and 12b are formed so that the pitch of the lattice fringes is smoothed by a 90 degree phase in order to discriminate the relative moving direction of both scales 10 and 12, respectively, and to perform signal division. Due to the relative movement of both scales 10 and 12, "bright" where the gratings match and "dark" where the gratings are shifted by n pitches and no light is transmitted appear periodically.
4 and is detected by photoelectric signals received by phototransistors 16a and 16b. Phototransistor 16a
, 16b are detected as a sine (sln) function signal and a cosine (cos) function signal, respectively, as shown in FIG. Therefore, by appropriately calculating and dividing the sine and cosine function signals, it is possible to measure the length of the object to be measured with the desired accuracy, and it is possible to provide an easy-to-read digital display based on the detected signal. It becomes possible. The period of the sine and cosine function signals is determined by the pitch P of 12 lattice stripes for each scale.
A pitch P of approximately m can be obtained, and by further signal-dividing this pitch P, an extremely highly accurate length measurement function can be obtained. Although a photoelectric type detector is illustrated in FIG. 1, the sine and cosine function signals shown in FIG. 2 can be detected in other electromagnetic or magnetic types as well in the conventional apparatus. As described above, the conventional device can perform highly accurate length measurement on the object to be measured without contact, but the detection signal of the detector is a sine or cosine function signal.
The detection signal draws a function curve that repeats increases and decreases in the length measurement direction, and as a result, there is a drawback that complicated signal processing is required to determine the length measurement force direction.

In other words, the sine and cosine function signals repeat increases and decreases for both force directions: the count increasing direction in which the main scale is moved in one force direction and the count decreasing force direction in which the main scale is moved in the opposite direction. , it is not possible to determine whether the count value is increasing or decreasing based on an increase or decrease in either one of the detection signals.In conventional devices, the above-mentioned increase or decrease can be determined by processing a combination of sine and cosine function signals. It was being done. Therefore, the conventional device has the disadvantage that signal processing becomes complicated and the number of signal divisions is restricted. Normally, in conventional devices, the number of signal divisions is limited to about 10 to 20, and as a result, when the checkered stripe pitch P is 20μ, it is possible to obtain only a minimum scale of about 1μ at most, and the minimum scale cannot be made smaller. Therefore, the grid pattern pitch P had to be made small, which led to drawbacks such as difficulty in scale processing. The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an improved signal detection circuit for a digital length measuring device that can easily increase the number of signal divisions with a simple configuration. be.

In order to achieve the above object, the present invention provides a function converter that converts a sine and cosine function signal corresponding to the length of a measured object obtained by a detector into a tangent (Tan) function signal, and and a multi-division AD converter that converts the tangent function signal into a digital signal divided by a desired number of divisions, and utilizes a single force directionality of increase or decrease corresponding to the scale relative movement direction of the fixed tangent function signal. This makes it possible to increase the number of effective divisions, improve measurement accuracy, and reduce the minimum scale. In the present invention, the function converter is preferably formed from a divider that divides a sine function signal and a cosine function signal, and the sine and cosine function signals are switched at a desired angular position by a signal switching circuit. It is preferable that the tangent function signal is always output as a tangent function signal in an angular range of 1 to 2 degrees, and the straight line part of the fixed tangent function signal is effectively utilized.

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

FIG. 3 shows a preferred embodiment of a signal detection circuit according to the present invention, in which the detection signals obtained from the conventional detector shown in FIG. 1 are applied to input terminals 20, 22.

The input signal to the terminal 20 is the A-phase, ie, the sine function signal (Slnθ) obtained from the phototransistor 16a, and the B-phase, ie, the cosine function signal (COSθ), obtained from the phototransistor 16b is supplied to the terminal 22. Ru. These A-phase and B-phase signals are supplied to the manual control circuit 24 and also to each switch of the switching circuit 26. The switching circuit 26 switches and combines the A-phase and B-phase signals in a desired combination according to the angle range of the detection signal, and includes eight switches SWl to SW8.
has. The A-phase signal at terminal 20 is connected to switches SWl and SW.
3 and is also supplied via an inverter 28 to switches SW5 and SW7. Similarly, B of terminal 22
The phase signals are supplied directly to switches SW2 and SW4 and via inverter 30 to switches SW6 and SW8. The switch group of the switching circuit 26 is controlled by on/off control signals 24-1 to 24-4 from the input control circuit 24, and controls the output signals from the switching circuit 26 to a desired combination in a desired angular range. The output of the switching circuit 26 is sent to the function converter 3 as a stop string function signal and a cosine function signal.
2 input terminals X and Y, and a function conversion is performed.

In the illustrated embodiment X, the function converter 32 consists of a divider that performs a division by one, so that a fixed tangent function signal is output.

As described above, in the illustrated embodiment, the sine and cosine function signals input as the A phase and B phase are converted into the fixed tangent function signals shown in FIG.
As is clear from the figure, the tangent function signal has better linearity and either increases or decreases in response to the direction of relative movement of the scale compared to the stop and cosine function signals in the conventional device shown in Figure 2. A specified unidirectionality is obtained, and as a result, it becomes possible to perform the signal division operation with a sufficiently large number of divisions compared to the conventional method using a simple processing circuit.

That is, according to the tangent function signal according to the present invention, the detection signal always has an increasing characteristic when the main scale moves in one direction, while it always has a decreasing characteristic when the main scale moves in the other direction. Therefore, it is possible to easily determine whether the count is increasing or decreasing by simply detecting an increase or decrease in the contact signal. However, as shown in FIG. 4, the sinusoidal signal has angles θ and ? It has the characteristic that it becomes discontinuous at π, and the error increases in the vicinity of these points. Therefore, in the illustrated embodiment, the switching circuit 26 selects only the tangent function signal in the angle range of 13 to 3. It is set to switch the combination of A-phase and B-phase signals for output. That is, the human control circuit 24 is
Four types of on/off control signals in one cycle angle range of ~2π. 24-1 to 24-4 to each switch SWl to SW8
As a result, the tangent function signal which is the output of the function converter 32 is a signal having unidirectionality that is switched every three times, and this tangent function The signal is shown in FIG.

As is clear from the above table and FIG. 5, according to the present invention, signal detection can be performed as four repeated tangent function signals having unidirectionality with respect to one pitch P of the detector, This detection signal is converted into an AD with a tangent function conversion function.
By converting using a converter, it is possible to obtain a count signal with less division distortion even if the number of signal divisions is increased.

The aforementioned switching of the switching circuit 26 at a predetermined angle is obtained from the A-phase and B-phase signals supplied to the input control circuit 24, an example of which is shown in the waveform of FIG. That is,
The solid line in Figure 6 is the A-phase (Slnθ) signal, and the chain line is the B-phase signal.
Indicates the phase (COSθ) signal, switching angle and ? At π, the values of both signals A and B have the same polarity and the same value, and similarly at switching angles 1π and 1π, they have different polarity and the same value, so both signals A and B are compared in the input control circuit 24. By doing so, the switching circuit 26
It becomes possible to output desired on/off control signals 241 to 24-4 to the terminals.

The tangent function signal output from the function converter 32 described above is supplied to the multi-division AD converter 34, divided by a desired number of divisions, and output as a digital signal. Multi-division AD converter 3
4 is an up/down counter 3 that can set the desired number of divisions.
6, and the up-down counter 36 is preset or reset to a desired division number by a preset signal or a reset signal from the input control circuit 24. The count value of the up-down counter 36 is converted to a tangent function converter 38.
After being converted into a tangent function signal, this signal is converted into an analog signal by a DA converter 40 and then sent to a comparator 4.
It is supplied to the inverting input terminal of No. 2. Since the non-inverting input terminal of the comparator 42 is supplied with the tangent function signal of the function converter 32 described above, the comparator 42 compares both input signals and sends the output directly to an AND gate 44 and then to an AND gate 46. Invert and supply. Since both AND gates 44 and 46 are supplied with a clock signal from a clock circuit 48, an up signal is supplied from the AND gate 44 and a down signal is supplied from the AND gate 46 to the up/down counter 36 according to the clock cycle. be done. Therefore,
If the tangent function signal obtained from the function converter 32 is larger than the comparison signal of the DA converter 40 through analog comparison in the comparator 42, the up-down counter 36 performs up-counting, and in the opposite case, down-counting. As a result, the multi-division AD converter 34 can perform multi-division digital conversion of the fixed function signal, which is a human-powered analog signal, into a desired number of divisions. Multi-division AD
Both outputs of the converter 34 are supplied to a damper circuit 50 and supplied to a display section 52 after the up-down count signal's increasing and decreasing oscillations are removed.

The damper circuit 50 includes two flip-flops 54, 56 and AND gates 58, 60, with an up count signal being supplied to an up counting AND gate 58 and a down count signal being supplied to a down counting AND gate 60. The up-count signal is further applied to the set input of the up-counting flip-flop 54 and the set input of the down-counting flip-flop 54, and the down-counting signal is also applied to the set input of the down-counting flip-flop 56 and the up-setting input of the up-counting flip-flop 54. has been done. Therefore,
If only one up-count signal or one down-count signal is input, which flip-flop 54,
56 is also only switched to the set state, and the AND gate 58,
No output is obtained from the AND gates 58 and 60, and an up-count signal or a down-count signal is output from the AND gates 58 and 60 only when two or more inputs are continuously supplied. By the damper circuit 50, it is possible to reliably prevent the occurrence of an increase/decrease oscillation in which up count signals and down count signals are alternately output one by one when there is no change in the input tangent function signal. . The up count signal and down count signal obtained as described above are counted by the display counter 62 of the display section 52, and the count value is digitally displayed by the digital display 64.

As described above, according to the present invention, the number of divisions can be increased by converting the detection signal into a fixed tangent function signal having unidirectionality.
It is possible to obtain a division number of about 00 to 200, and it is possible to obtain a significantly finer minimum scale compared to conventional signal detection circuits using sine and cosine function signals, and as a result, the configuration of the signal detector is simplified. It is also possible to do so. In the illustrated embodiment, an angular range of 13 to 3 is selected to utilize the straight line portion of the tangent function signal, but this angular range can be arbitrarily selected.

As explained above, according to the present invention, it is possible to significantly increase the number of signal divisions by simply adding a simple function unit using a conventional detector for detecting stop string and cosine function signals. It becomes possible to obtain a highly accurate digital sensor with a simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main parts of a photoelectric detector in a conventional digital length measuring device, Fig. 2 is a waveform diagram showing sine and cosine signals obtained from the conventional device of Fig. 1, and Fig. 3 is A circuit diagram showing a preferred embodiment of the signal detection circuit according to the present invention, FIG. 4 is a waveform diagram showing a fixed contact function signal in the present invention, and FIG. 5 shows switching in a predetermined angle range in the embodiment of FIG. FIG. 6 is a waveform diagram showing the combined tangent function signal, and FIG. 6 is a waveform diagram showing on/off control of the switching circuit by the input control circuit in FIG. 26...Switching circuit, 32...Function converter, 34...Multi-division AD converter, 52...
...Display section.

Claims (1)

[Claims] 1 includes a main scale having length measurement grid stripes arranged in alignment, and an index scale having a pair of gate grid stripes that are moved relative to the main scale and have a phase pitch different by 90° in the direction of movement; In a signal detection circuit of a digital length measuring device, which receives the amount of relative displacement as transmitted light or reflected light from the main scale, and detects the length of the object to be measured as a sine or cosine function signal,
A signal switching circuit that switches and outputs sine and cosine function signals in a predetermined combination, a function converter that converts the predetermined combination of sine and cosine function signals output from the signal switching circuit into a tangent function signal, and an output from the function converter. The tangent function signal to be −
An input control circuit that controls the signal switching timing of the signal switching circuit so that the tangent function signal becomes a tangent function signal in the angular range of π/4 to π/4, and a tangent function signal output from the function converter is divided by a desired number of divisions. A signal detection circuit for a digital length measuring device, comprising: a multi-division AD converter for converting into a digital signal.