JPH08219754A - Length measuring apparatus - Google Patents

Abstract

PURPOSE: To obtain a small-sized inexpensive length measuring apparatus which can output three-phase U, V, W signals. CONSTITUTION: An AB signal outputted from a scale circuit 1 is subjected to pulsation and counted by means of a counter 3. When a decoder 4 detects a predetermined count of the counter the decoder 4 outputs three-phase U, V, W signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a length measuring device for measuring a displacement amount such as a movement amount between two objects, and is particularly suitable for application to a linear motor scale.

[0002]

2. Description of the Related Art In a machine tool or the like, it is extremely important to accurately measure the amount of movement of a tool with respect to a workpiece, and various measuring devices have been commercialized for this purpose. As one of them, an optical scale using moire fringes obtained by superposing two optical gratings has been conventionally known. As shown in FIGS. 4 (a) and 4 (b), this optical scale includes a main scale 101 in which a grid is provided on one surface of glass so that a light-transmitting portion and a non-light-transmitting portion are arranged at a predetermined pitch. An index scale 102 is provided on one surface of which a light-transmitting portion and a non-light-transmitting portion are arranged at a predetermined pitch, and the index scale 102 is opposed to the main scale 101 with a minute interval. The index scale 102 is tilted by a small angle with respect to the lattice of the scale 101.
The grid is arranged.

The lattices provided on the main scale 101 and the index scale 102 are formed by scribed lines having the same pitch formed by vacuum-depositing chromium (Cr) on one surface of glass and etching it. When the main scale 101 and the index scale 102 are arranged so as to face each other with a minute gap, moire fringes as shown in FIG. 6 occur. The cycle of this moire fringe is W
Therefore, a dark portion or a bright portion is generated every cycle W. The dark part or the bright part moves from the top to the bottom or from the bottom to the top according to the direction in which the index scale 102 moves left and right relatively to the main scale 101.

In this case, when the pitch of the gratings of the main scale 101 and the index scale 102 is P and the mutual inclination angle is θ [rad], the cycle W of the moire fringes is expressed as W = P / θ, and the moire fringes are shown. The period W of the
Is a cycle that is expanded by 1 / θ times. Therefore, when the grating moves P, the moire fringes move W, and by reading the expanded change in W, the amount of movement of the grating can be accurately measured.

Therefore, as shown in FIG. 5A, the light emitting element 103 and the light receiving element 105 are provided in the head main body 106 provided with the index scale 102 in order to optically detect the change of the moire fringes. . That is, as shown in FIG. 2B, a light emitting element (light source) 103 is provided on the opposite side of the main scale 101, and the light from the light emitting element 103 that transmits the moire fringes is received by the light receiving element (photoelectric conversion element) 10.
The light is received at 5, and the change in the moire fringes is optically detected.

In this case, while moving the index scale 102 relative to the main scale 101,
When the change in the current flowing through the photoelectric conversion element 105 is read,
As shown in FIG. 7, it changes like a sine wave. Therefore, as shown in FIG. 6, when the two photoelectric conversion elements 107 and 108 are provided with a shift of 90 ° from one cycle W,
As shown in FIG. 7, the current flowing in the B-phase photoelectric conversion element 108 has a sin wave, whereas the current flowing in the B-phase photoelectric conversion element 108 has a cosine wave.

In this case, depending on the relative movement directions of the main scale 101 and the index scale 102, A
Since the phase of the current flowing in the B-phase photoelectric conversion element 108 with respect to the current flowing in the phase photoelectric conversion element 107 is 90 ° advanced or 90 ° delayed, two photoelectric conversion elements arranged with a 90 ° shift are provided. And the relative movement direction can be detected by detecting the phase between the two. In addition, one period P of these two A-phase signals and B-phase signals is equal to the pitch P of the grating and the index scale 102.
Corresponds to the movement, and the moving distance of the index scale 102 can be measured by shaping the waveforms of the A-phase signal and the B-phase signal and counting them by the counter.

By the way, in some machine tools and the like, a tool is moved with respect to a workpiece by a linear motor. In this case, a three-phase motor magnetic pole sensor signal (U,
V, W) are generally required. An example of the structure of the scale of the conventional length measuring apparatus in this case is shown in FIG. In the scale 200 shown in this figure, the origin engraving line 201 detects the origin because the detection of moire fringes described above is basically incremental and the coordinates change when measurement is not continuously performed. Then, it is a marking line provided to reproduce the original coordinate system.

Further, 202 is an AB signal marking line for outputting two signals of A phase and B phase, and 203 is a UVW signal marking line for obtaining a three-phase UVW signal which is a motor magnetic pole sensor signal. is there. In this way, the origin signal, the AB signal, and the UVW signal are obtained from the sensor 204 by detecting the information of each marking line provided on the scale 200 by the optical sensor 204 as shown in FIG. There is. According to this configuration, a three-phase UVW signal, which is a motor magnetic pole sensor signal, can be obtained. However, since the marking line for the UVW signal is required, the outer shape of the scale 200 becomes large and each linear motor type is different. In many cases, the magnetic pole pitches are different, and there is a drawback in that a scale original plate corresponding to the magnetic pole pitch is required.

FIG. 9 shows an example of the structure of a scale of another conventional length measuring apparatus. The scale 210 is provided with an origin marking line 201 and an AB signal marking line 202,
A UVW signal sensor line 206 for obtaining a three-phase UVW signal which is a motor magnetic pole sensor signal is separately provided. The origin signal and the AB signal are obtained from the sensor 205, and the UV is emitted from the sensor 207.
The W signal is obtained. According to this configuration, a three-phase UVW signal can be obtained without increasing the scale outer shape. Further, by changing the pitch of the UVW signal sensor line, it is possible to deal with linear motors having different magnetic pole pitches.

[0011]

However, according to the length measuring apparatus shown in FIG. 9, two types of position sensors are required, so that the mounting space becomes large and
There was a problem that the cost increased. Therefore, in the present invention, the installation space does not increase and the three-phase U
It is an object of the present invention to provide an inexpensive length measuring device that can obtain a VW signal.

[0012]

In order to achieve the above object, a length measuring apparatus according to the present invention includes a scale circuit that outputs a signal that periodically changes according to a deviation amount, and a scale circuit that outputs the signal. Counter to pulse the signal to count
A decoder that outputs a three-phase signal by detecting that the count value of the counter has reached each of a plurality of predetermined values is provided. Further, in the above length measuring device, the decoder may be provided with setting means for setting a plurality of arbitrary predetermined values.

[0013]

According to the present invention, a three-phase UVW signal can be obtained without providing a marking line for obtaining a three-phase UVW signal which is a linear motor magnetic pole sensor signal. The outer shape can be made small. Further, the same scale as the conventional increment type scale can be used, and the scale can be manufactured at low cost. Furthermore, by allowing the predetermined value of the decoder to be set arbitrarily, it becomes possible to easily cope with a change in the magnetic pole pitch of the linear motor.

[0014]

1 is a block diagram showing the configuration of an embodiment of the length measuring apparatus of the present invention. In this figure, 1 is the same as in FIG.
And a scale circuit for outputting an AB signal composed of two signals of A phase and B phase, a battery for backing up the scale circuit 1 and the counter 3, and a pulse-shaped AB having a waveform shaped waveform. A counter for counting signals 4 is a decoder for decoding the count value of the counter 3 to output a three-phase UVW signal.

In the length measuring device thus constructed,
The deviation amount to be measured can be measured by the same method as the conventional method using the AB signal output from the scale circuit 1 according to the deviation. In this case, the battery 2 that backs up the scale circuit 1 allows the scale circuit 1 that basically performs the incremental detection to operate as an absolute scale.

AB output from the scale circuit 1
The signal is waveform-shaped into a pulse shape and counted by the counter 3. Since this count value is proportional to the deviation amount, that is, the movement amount of the rotor of the linear motor, the decoder 4 can decode this count value to create a three-phase UVW signal. Further, the counter 3 shown in FIG. 2 will be described in detail with reference to FIG.
The counter 3 counts the pulse-shaped AB signal after the waveform shaping inputted to the counter 3, and the counted values are a at time t1, b at time t2, c at time t3, d at time t4, and e at time t5. , F at time t6, g at time t7, h at time t8, and i at time t9.

Then, as shown in FIG. 2, the decoder 4 detects the count value a and raises the U-phase signal, and detects the count value d and lowers the U-phase signal. Further, the decoder 4 detects the count value c to raise the V-phase signal, detects the count value f to lower the V-phase signal, and detects the count value e to detect W.
The phase signal is raised, the count value h is detected, and the W-phase signal is lowered. Similarly thereafter, the decoder 4 detects the count value of the counter 3 and creates and outputs the UVW signal as shown in FIG. As a result, a three-phase UVW signal can be obtained without providing a special marking line or the like for obtaining the UVW signal on the scale. Also, no special sensor is needed to obtain the UVW signal. The battery 2 also backs up the count value of the counter 3 so that accurate UVW signals of three phases can be obtained without phase shift.

Next, a modified example of the length measuring apparatus of the present invention is shown in FIG. 3, in which only the configuration of the portion for obtaining the UVW signal is shown. In this modification, unlike the configuration shown in FIG. 1, the setting means 5 is provided in the decoder 4. By doing so, the detection value of the count value for obtaining the UVW signal can be arbitrarily set, so that even if the magnetic pole pitch of the linear motor is changed, the setting value can be simply changed by the setting means 5. Will be able to deal with. A rotary switch or the like that outputs a digital signal can be used as the setting means 5.

[0019]

As described above, according to the present invention, a three-phase UVW signal can be obtained without providing a marking line or the like for obtaining a three-phase UVW signal which is a linear motor magnetic pole sensor signal. The external shape of the scale of the long device can be made small. In addition, the same scale as the conventional increment type scale can be used, and the scale can be manufactured at low cost. Furthermore, by allowing the predetermined value of the decoder to be set arbitrarily, it becomes possible to easily cope with a change in the magnetic pole pitch of the linear motor.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a length measuring apparatus of the present invention.

FIG. 2 is a waveform diagram for explaining that the length measuring device of the present invention can generate a UVW signal.

FIG. 3 is a block diagram showing a configuration of a modified example of the length measuring apparatus of the present invention.

FIG. 4 is a diagram schematically showing a scale of a conventional optical scale.

FIG. 5 is a diagram showing a principle structure of a conventional optical scale.

FIG. 6 is a diagram for explaining moire fringes generated on an optical scale.

FIG. 7 is a diagram showing a relationship between a relative position of a main scale and an index scale and an output current.

FIG. 8 is a diagram showing an example of a scale for obtaining a conventional UVW signal.

FIG. 9 is a diagram showing another example of a scale for obtaining a conventional UVW signal.

[Explanation of symbols]

 1 scale circuit 2 battery 3 counter 4 decoder 5 setting means

Claims (2)

[Claims] 1. A scale circuit that outputs a signal that periodically changes according to the amount of deviation, a counter that pulse-counts the signal output from the scale circuit, and a count value of the counter that is a plurality of predetermined values. A length measuring apparatus comprising: a decoder that outputs a three-phase signal by detecting that each of the values has been reached. 2. The length measuring apparatus according to claim 1, wherein the decoder is provided with setting means for setting a plurality of arbitrary predetermined values.