JPH0374770B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a photoelectric displacement detection device, and particularly to a photoelectric displacement detection device that can achieve a stable detection action and has improved frequency response characteristics.

[Prior art] Dial gauge micrometers with digital display, length measuring devices such as three-dimensional measuring machines, laser microphones that use laser beams to measure distances, table feeding devices for NC machine tools, etc. A mold displacement detection device is used, and a detection device with excellent measurement accuracy and durability has been put into practical use.

FIG. 1 shows the main parts of this type of displacement detection device, in which a main scale 10 made of glass or a thin stainless steel plate has a plurality of length measurement slits 10a and absolute value slits 10b aligned and arranged on its surface. A desired length measurement or position detection operation is performed along this main scale 10.

An index scale 12 and an absolute value scale 13 are provided near the main scale 10, and the index scale 12 and absolute value scale 13 have the length measuring slits 10a,
Index slits 12a, 12b, 13a corresponding to the absolute value slit 10b are provided, and the amount of slit movement is electrically detected by the relative movement of each scale 10, 12, 13, and this relative movement signal is Based on this, a length measurement or position detection function is achieved.

In order to photoelectrically convert the relative movement of each scale 10, 12, 13, each scale 10, 12, 13
In the figure, since it is a transmission type measurement device, light emitting devices 14a, 14b, and 14c are provided on the main scale 10 side, and a light emitting device 1 is provided on the index scale 12 side.
6a, 16b, and a light receiver 16c is provided on the absolute value scale 13 side, and these light emitting/receiving devices 14, 16
are the index slits 12a, 12b, 1
It is placed at a position corresponding to 3a. As is well known, both index slits 12a and 12b are arranged to be offset by half a pitch from each other, so that the light transmitted through both scales 10 and 12 is a sine wave signal on one side and a cosine wave signal on the other. The signal is detected as a wave signal, and it is possible to perform a desired division operation using both signals having different phases.

Further, the above-mentioned absolute value scale 13 can output the moving position of the main scale 10 as an absolute value signal in cooperation with absolute value slits 10b which are provided intermittently on the surface of the main scale 10 and indicate the absolute value. , it is possible to know where the absolute value scale 13 is located on the main scale 10.

As described above, according to the conventional device, photoelectric conversion of the amount of displacement is performed, and then the relative displacement signal detected in this manner is subjected to necessary processing by the circuit shown in FIG. be done.

FIG. 2 shows an example in which the displacement detection device is used as a length measuring device, in which the relative movement displacement signals of each light receiver 16 are amplified by preamplifiers 18a, 18b, and 18c, and then processed by a circuit. 20. The detection circuit 20 includes a waveform shaping circuit 22 and a dividing circuit 24, and as is well known, the dividing circuit 24 combines both the sine wave signal and the cosine wave signal into a measurement pitch smaller than the slit width of the scales 10 and 12. The division is done.

The output of the detection circuit 20 is supplied to a digital display 28 via a counter 26, where the measured length is digitally displayed and, if necessary, a printer 3.
0 records the measured length.

In addition, the three light emitters 14a, 14b,
14c are resistors 31a and 3 that respectively limit the current.
It is connected to a power source via 1b and 31c, and the desired light emitting action is performed.

At the above-mentioned displacement detection position, the amount of light from the light emitter 14 has a great effect on the characteristics of the photoelectric conversion section, and for this reason, a constant light emitting action with a stable amount of light is required. Therefore, in the conventional device, for example, in the case of the device shown in FIG. 2, the resistor 31 connected to each light emitter 14 is finely adjusted,
At the same time, the output of each detection signal supplied to each detection circuit 20 is initially adjusted by adjusting the preamplifier 18 as necessary.

However, even with the initial adjustment performed before the measurement, the conventional device has the disadvantage that if the power supply voltage itself fluctuates, the amount of light emitted changes, and errors often occur in the detected value. It was hot.

In addition, as a conventional detection device for table feed control of NC machines, a detection section is provided for each NC movement axis, and this is centrally controlled by a power supply, operation switch, display, etc. installed on the fixed side. is becoming common.

Figure 3 shows an example of this type of NC control device, in which the photoelectric displacement detection devices shown in Figures 1 and 2 are installed for each of X, Y, and Z of the NC machine. , a light emitter 1 is placed at the moving part in each axis direction.
4. The light receiver 16 and the preamplifier 18 are integrated into the movable housing 32.

The fixed housing 34 includes a power supply 36, a detection circuit 20, and indicators 38, 40, 4 for each axis.
2 is provided.

The movable housings 32 are provided individually for each of X, Y, and Z, and are attached to the respective NC feed axes. Therefore, according to such a split-type detection device, which is electrically connected,
The power supply, operation switch group, and display section can be commonly installed on the fixed side, which greatly contributes to miniaturization of the device.

However, in such split-type detection devices, the length of the cable 44 that connects the fixed housing 34 and the movable housing 32 varies depending on the device, and furthermore, as shown in FIG. X, Y,
When there are multiple types of movable side devices such as Z, a situation occurs where the cable length changes for each axis, and because of this, the voltage on the solid side is not constant due to the voltage drop within the cable 44. Even if there is a problem, there is a problem in that the amount of light from the light emitters provided on each movable side actually varies, and as a result, a non-negligible error is introduced into the measurement accuracy. As explained above, in the past, it was not always possible to obtain a stable supply current due to fluctuations in the power supply voltage or voltage drop to the light emitter, especially in a detection device that is divided into multiple detection sections. However, there was a problem in that the variation became large, which had a non-negligible negative effect on detection accuracy.

As an improved conventional device, it has been proposed to provide a voltage detector in the slider unit on the movable side and a device to control the power supply voltage, or to provide a separate constant power supply device in the slide unit. However, it is necessary to newly install cables, voltage detectors, and other complicated structures to guide the detection voltage, and there is also the problem that noise is mixed into the voltage detection and control lines. Further, the separate power supply device also had various problems such as having a negative effect on the sliding characteristics of the slider unit and increasing the size of the device.

In addition, in the installation structure of multiple detection units on the movable side described above, the actual voltage inside the movable side slider unit decreases by 4 to 6% due to cable loss compared to the power supply voltage on the fixed side, for example, 5 volts. , the amount of light from the light emitter also decreases by 10 to 15%, and if we take into account that the fixed side power supply voltage fluctuation is 5% up and down, the amount of emitted light may decrease by nearly 20%. It is clear that this significantly degrades the S/N ratio of the length measurement signal and has a large adverse effect on measurement accuracy.

Furthermore, according to the conventional device, length or position information can be output as an electrical signal that is photoelectrically converted by the relative movement between the main scale 10 and the index scale 12, and this can be used for a desired purpose. In recent years, in high-precision detection devices, a major problem has arisen in the response speed of the devices.

That is, in recent years, there has been a demand for a reduction in power consumption in detection devices, and power saving has become a major issue for devices, especially in battery-powered portable length measuring devices and the like. Generally, in a photoelectric conversion device, a light emitting device consumes a large amount of power, and it has been desired to reduce this power consumption.

Furthermore, according to the scale arrangement shown in FIG. 1, it has been a major requirement in assembling equipment or processing parts to increase the clearance between the scales that move relative to each other to some extent. Due to the various factors mentioned above, the amount of light received by the photoreceiver side of the detection device tends to decrease. Various improvements have been made to the detection circuit 20 connected to the device.

In normal cases, in order to obtain a detection signal that can be sufficiently processed even with a small amount of received light, a load resistor 46 having a relatively large resistance value R _L is installed at the emitter of the light receiver 16, as shown in FIG. is connected and the voltage Vo is extracted from the midpoint between the emitter and the load resistor 46, thereby obtaining a detected voltage having a voltage value that is easy to process in subsequent stages.

However, on the other hand, large resistance values
The load resistor 46 of R _L is connected to the light receiver 16.
When a phototransistor is used as a phototransistor, there is a problem in that its response frequency is severely restricted. That is, as shown in FIG. 4, the response frequency f of the phototransistor 16 is determined by the electric capacitance Cj of the phototransistor 16 and the resistance value R _L
Therefore, it is determined by f=1/(2πCjR _L ), and as is clear from the formula for the response frequency f, an increase in the load resistance value R _L due to the above-mentioned reason results in a decrease in the response frequency f, and in the conventional device, There is a trade-off between reducing power consumption and improving response frequency, and there has been a strong demand for a device that satisfies both.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to improve the frequency response characteristics without increasing power consumption, and to improve the frequency response characteristics regardless of fluctuations in power supply voltage or cable loss. The first object of the present invention is to provide an improved photoelectric displacement detection device that can increase detection speed by controlling the amount of light from a light emitter to be constant.

[Structure of the Invention] In order to achieve the above object, the present invention provides a photoelectric deflection detection device comprising a device main body, a deflection detection section, and a cable connecting the main body and the deflection detection section. The main body of the apparatus includes a detection power source that supplies power to the deflection detecting section via the cable, and a signal processing unit that calculates the displacement amount of the object to be measured based on the signal from the deflection detecting section. The deviation detection section includes an optical grating that moves together with the object to be measured, a light emitter group that irradiates detection light toward the optical grating, and a light emitting circuit that drives the light emitter group to emit light. and provided for each of the light emitters,
A photoreceiver group consisting of a plurality of phototransistors that receives reflected light or transmitted light from the optical grating, amplifies the received light signal from the phototransistor, and transmits the amplified received light signal to the device main body via the cable. a photoelectric deflection detection device, the light emitting circuit includes a group of current limiting resistors that are connected in series for each of the light emitters and that limits the current of each of the light emitters; A current control transistor group that is connected in series for each light emitting device and controls the current of each light emitting device, and a voltage across one of the resistors of the current limiting resistor group is monitored, and the current control transistor group is connected in series. and one shunt regulator that controls the current flowing through each of the light emitters to a constant value, and the light receiving circuit has a grounded base connected in cascade to the output terminal of each of the phototransistors. and a preamplifier that amplifies the light reception signal output from the common base type transistor and sends it to the main body of the device via the cable.

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

FIG. 5 shows a three-axis split type device for an NC machine to which the displacement detection device according to the present invention is applied, and the same members as those in FIG.

A characteristic feature of the present invention is that the light emitting devices 14 are supplied with their light emitting current by a constant current circuit, and this constant current circuit is connected to each light emitting device 14.
Transistors 48a, 48b, connected in series to
48c and resistors 50a, 50b, and 50c, and an unstable power supply including fluctuations and voltage drops supplied from the fixed side is supplied to this light emitting circuit.

In order to stabilize the constant current light emitting circuit including the transistor 48, in the present invention, the light emitting circuit includes a constant voltage circuit, and this constant voltage circuit includes a shunt regulator 52. The shunt regulator 52 used in the example is
TI's TL431C is used, and a constant voltage is output to its constant voltage terminal R. shunt regulator 52
The cathode input terminal K is connected to the positive terminal of the power supply via a resistor 54, and the anode terminal A is connected to the negative terminal.

Further, in the present invention, the cathode input terminal K of the shunt regulator 52 is connected to the base of each transistor 48, and the constant voltage terminal R mentioned above is connected to the emitter of the transistor 48.

The photodetector 16 in FIG. 5 uses a phototransistor (for example, PT501), and as shown in FIG. 6, a transistor 56 whose collector is connected to the power supply and whose emitter is grounded as a base
It is characterized in that it is connected to a load resistor 46 via. That is, in the present invention, the photodetector 16 made of a phototransistor is connected to the load resistor 46 after its impedance is converted by the common-base transistor 56, and the common-base transistor 56 is cascade-connected with the phototransistor 16. has been done.

As is clear from the figure, phototransistor 1
The emitter of transistor 6 is connected to the emitter of transistor 56, the base of which is grounded, and the collector thereof is grounded via load resistor 46. A detected voltage is taken out from the midpoint between the collector of the common base transistor 56 and the load resistor 46.

The structure of the present invention is clear from the above description,
The effect will be explained below.

Due to the constant voltage action of the shunt regulator 52 described above, the supply current i flowing to the light emitting device, that is, the light emitting diode 14c, is determined by the voltage at the constant voltage terminal R of the shunt regulator 52, where the resistance value of the resistor 50c is r, and the voltage at the constant voltage terminal R of the shunt regulator 52 is If V _R is used, it can be obtained as i=V _R /r.

Therefore, by including a constant voltage circuit using the shunt regulator 52 in the light emitting circuit as in the present invention, the shunt regulator 52 can be controlled even by fluctuations in the cable flow or fluctuations in the power supply voltage itself. Since a constant voltage V _R is output to the constant voltage terminal R,
As a result, the supply current i for light emission is always maintained at a constant value.

Furthermore, even if the characteristic characteristics of each transistor 48 slightly fluctuate due to temperature changes or the like, the cathode input terminal K of the shunt regulator 52 changes in accordance with the fluctuations, so that the constant voltage terminal R
It is clear that the voltage V _R of remains constant,
In this embodiment, the shunt regulator 52
Since the cathode input terminal K of the transistor 48 is connected to the base of each transistor 48, even if the reference voltage of the constant voltage terminal R is connected only to a single light emitting circuit, that is, the light emitting circuit of the light emitter 14c, other current control transistors Desired constant current control is also given to the base inputs of 48a and 48b, making it possible to obtain a constant current common to all light emitters 14.

Of course, in the present invention, the shunt regulator 52 is connected to each light emitter 14a, 14b, 14c.
It is also possible to provide one for each.

In actual circuit configuration, the transistor 4
It is preferable to select resistors 8a, 48b, and 48c with approximately the same characteristics, and resistors 50a and 50
The resistance values of b and 50c are initially adjusted and set to the same value.

As described above, according to the present invention, the supply current of the light emitter is controlled using a constant voltage circuit including a shunt regulator, and it is possible to control the current supplied to the light emitting device by using a constant voltage circuit including a shunt regulator. Therefore, it is possible to always obtain a stable amount of light emitted even in the case of light emission, and good detection accuracy can be achieved.

In addition, in FIG. 5, due to the impedance conversion of the common base transistor 56, although the output side resistor 46 has a relatively large resistance value R _L as in the conventional case, its input impedance
hib can be set to a value sufficiently smaller than the resistance value _RL . Therefore, in the present invention, the response frequency f of the photodetector 16 made of a phototransistor is f=1/(2πCjhib), and the input Impedance hib is resistance value R _L
Since it is sufficiently smaller, the response frequency can be significantly improved.

In order to compare the conventional device shown in FIG. 4 and the embodiment of the present invention shown in FIG.
When using 5V, a phototransistor (PT501) as a photoreceiver, and a 5kΩ load resistor R _L , the response frequency of the conventional device is
25KHz, whereas in the present invention, if 2SA1048 is used as the cascade-connected transistor and the base common voltage is 2.5V, the response frequency will be 100KHz, and the response frequency can be expanded to four times the frequency width. did it.

By improving the response frequency, it becomes possible to sufficiently increase the relative movement speed of both scales. For example, each slit of the main scale and index scale has a light transmission length of 10 microns and a light transmission length of 10 microns. In terms of cut-off length, the limit of relative movement speed in conventional equipment is 500 mm per second, but according to the present invention, the speed can be increased to 2000 mm per second, which is equivalent to the automatic feed of high-speed NC machine tools in recent years. It is understood that it is possible to follow up sufficiently.

As shown in FIG. 5, by incorporating a constant voltage circuit including the shunt regulator into the housing 32 of the movable slider unit, a constant current can be supplied near each light emitting device. This is extremely suitable for a detection device in which the fixed side and movable side are separated.

It goes without saying that the present invention can also be applied to a hologram scale method without an index scale.

[Effects of the Invention] As explained above, according to the present invention, by connecting a constant current circuit to a light emitter and cascading a transistor whose base is grounded to a light receiver, fluctuations in power supply voltage and other fluctuation factors can be suppressed. This has the effect of eliminating fluctuations in the current supplied to the light emitting device due to this, improving frequency response characteristics without increasing power consumption, and increasing detection speed.

Furthermore, from the above, when the optical grating is used at a feed rate below a predetermined value, the slit width of the optical grating can be made denser than before, thereby simplifying the dividing circuit side.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the main parts of a slider section in a general photoelectric displacement detection device, Fig. 2 is a block diagram of a light receiving circuit, light emitting circuit, and signal processing circuit suitable for Fig. 1, and Fig. 3 is a conventional one. An explanatory diagram showing an example of a detection device for NC machines in which a fixed side and a movable side are separated. Fig. 4 is a circuit diagram showing a part of a conventional light receiver and detection circuit. Fig. 5 6 is an explanatory diagram showing a preferred embodiment of the displacement detection device according to the present invention used in an NC machine, and FIG. FIG. 10... Main scale, 12... Index scale, 13... Absolute value scale, 14...
Light emitter, 16... Light receiver, 18... Preamplifier,
20...detection circuit, 22...waveform shaping circuit, 24
... Divided circuit, 26 ... Counter, 28 ... Digital display, 30 ... Printer, 32 ... Movable side housing, 34 ... Fixed side case, 36 ... Power supply, 3
8, 40, 41...display unit, 44...cable,
44...Resistor, 48...Transistor, 50...
Resistor, 52... Shunt regulator, 54...
Resistor, 56...transistor.

Claims (1)

[Scope of Claims] 1. A photoelectric deflection detection device comprising: a main body; a deflection detecting section; and a cable connecting the main body and the deflection detecting section; a detection power source that supplies power to the deviation detection unit via the deviation detection unit; and a signal processing circuit that calculates the displacement amount of the object to be measured based on the signal from the deviation detection unit, and the deviation The detection unit includes: an optical grating that moves together with the object to be measured; a group of light emitters that irradiates detection light toward the optical grating; a light emitting circuit that drives the group of light emitters to emit light; and a light emitting circuit provided for each of the light emitters. a photoreceiver group consisting of a plurality of phototransistors that receive reflected light or transmitted light from the optical grating; amplify the received light signal from the phototransistor; In a photoelectric deflection detection device, the light emitting circuit includes a current limiting resistor group connected in series for each of the light emitters and limiting the current of each of the light emitters. , a group of current control transistors that are connected in series to each of the light emitting devices and control the current of each of the light emitting devices; and a group of current control transistors that monitors the voltage across one of the resistors of the group of current limiting resistors; a shunt regulator that collectively controls the current flowing through each of the light emitters to maintain a constant value, and the light receiving circuit is cascade-connected to the output terminal of each of the phototransistors. A photoelectronic device comprising: a plurality of base-grounded transistors; and a preamplifier that amplifies the received light signal output from the base-grounded transistor and sends it to the main body of the device via the cable. Mold deviation detection device.