JP2524390B2 - Linear displacement detector - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a linear displacement detector, and in particular, it is possible to easily perform calibration in a short time, and therefore, it is possible to improve the accuracy of the entire system including a machine tool and the detector. It relates to a displacement detector.

[Prior art]

An illumination system including a light source and a light-transmitting index scale in which a main scale having a periodic main lattice is fixed to one of the facing members and a corresponding periodic sub-lattice is formed on the other member. And a detection head including a light receiving element that photoelectrically converts light from the illumination system modulated by the main grating and the sub grating, and a detection signal that periodically changes according to relative displacement of both members. Photoelectric displacement detectors that generate the are widely used in the field of measuring the feed amount of a tool of a machine tool. FIG. 8 shows an example of a conventional reflection type photoelectric displacement detector, which includes a light emitting diode 10 as photoelectric and a collimator lens 12 which makes light emitted from the light emitting diode 10 into a parallel illumination light beam. A main scale 14 having a periodic main grating 16, and a light-transmissive index scale 18 having a corresponding periodic sub-lattice 20 disposed so as to be movable relative to the main scale 14, And a light receiving element 22 for photoelectrically converting a reflected light ray R from the parallel illumination system that has been reflected by the main grating 16 of the main scale 14 and has passed through the sub grating 20 of the index scale 18. A periodic displacement detection signal is generated according to the relative displacement of the scale 14 and the index scale 18. Here, the main scale 14 is housed in, for example, a frame body and is fixed to one member that moves relatively, for example, a bed of a machine tool, and the light emitting diode 10, the collimator lens 12, the index scale 18, and the light receiving element 22.
Is housed in the detection head 24 and fixed to the other member that moves relatively, for example, a tool. Such linear displacement detectors are rarely used in a completely stable state, and the difference in thermal expansion due to changes in the operating environment temperature (the line between the measurement target, which is the work or mounting machine, and the main scale). Difference in expansion coefficient, difference in heat capacity between measurement target and main scale, difference in temperature rise due to this),
The apparent accuracy changes due to unstable and uncontrollable error factors such as changes in the straightness of motion of the machine and thermal deformation of the mechanical structure. That is, due to the thermal expansion and the like due to the change of the operating environment temperature, not only the accuracy of the linear displacement detector itself changes due to the thermal expansion and contraction of the main scale, but also the accuracy of the movement of the machine tool or the like to be measured. Due to the change, the linear displacement detector has a composite error of both. In order to eliminate the above-mentioned complex error and improve the accuracy of the entire system including the linear displacement detector and the machine tool, the following method is used. One of them is a method of electrically correcting in the signal processing stage, for example, by providing the NC controller with a correcting function and using an error table preset corresponding to the absolute coordinates in the slot talk, as shown in FIG. As shown, the so-called pitch error correction, which improves the overall accuracy by adding or subtracting the correction value to or from the measured value, or the interval Y between two points is precisely measured in advance using a reference device, As shown in the formula, the so-called mechanical error correction, in which the measured value X obtained by the linear displacement detector is multiplied by the correction coefficient β obtained by the precise measurement to perform the linear correction, corresponds to this. Y = β · X (1) Further, there is also a method of correcting by operating the main scale of the linear displacement detector. For example, a method of correcting the main scale by bending it with an adjusting screw at a certain pitch, or a main scale There is also a method of linearly correcting by pulling or compressing the scale. For the correction, it is desirable that the stroke is divided into several sections and finely corrected by polygonal lines. However, since the design of the thermal object of the machine tool is progressing in recent years, the linear correction alone is sufficient for practical use. However, both methods require a reference device such as a check master or a laser length measuring device to obtain the accuracy of the entire system, and even if linear correction is performed, these must be used to obtain the correction value. Therefore, expensive precision equipment that can be used as a standard is required. Also, for example, it is necessary to place a calibration tool on the table of a machine tool, measure the distance between the calibration tools with a standard instrument, and also measure it with a linear displacement measurement instrument, and obtain the correction coefficient β from the ratio of the two. Will be very troublesome. Furthermore, since the error curve is constantly changing and is not the only absolute curve, it is necessary to periodically perform calibration work, but during the calibration work, both workers and machine tools are out of production, There is also the problem of cost-up, and even if the system accuracy changes due to environmental changes, calibration work may not be performed. Especially in small factories, the burden of calibration work is heavy, and only initial calibration is required at the time of shipment or installation.
After that, it was left uncalibrated, and in many cases the desired overall accuracy was not obtained. Further, in the case of the pitch error correction, it is necessary to obtain the correction data with a fine pitch in advance by using an expensive reference device such as a laser length measuring device or a chip exmaster, and the value of the correction data changes. However, there is also a problem that measured values are discontinuous.

[Problems to be achieved by the invention]

The present invention has been made to solve the above-mentioned conventional problems, and uses a member having desired expansion and contraction characteristics,
By using the drive mechanism of the device, it is possible to easily calibrate the error due to expansion and contraction of the main scale in a short time, thus providing a linear displacement detector that can improve the accuracy of the entire system. The purpose is to do.

[Means for achieving the object]

The present invention has a main scale fixed to one member that relatively moves and a detection head that is fixed to the other member that relatively moves, and displacement detection obtained by a displacement detection sensor of the detection head. In a linear displacement detector that electrically measures the relative displacement between both members by a signal, the expansion and contraction characteristics are different from the main scale mounted in an expandable and contractable state substantially parallel to the main scale, and the desired expansion and contraction characteristics are obtained. A calibration gauge having the calibration gauge and a calibration sensor attached to the detection head for detecting a variation in the spacing at a predetermined position on the calibration gauge are provided, and the variation in the spacing detected by the calibration sensor. The calibration gauge is used to correct the measurement value based on the displacement detection signal in accordance with the amount, thereby achieving the above object. Further, in the same linear displacement detector according to the present invention, the main scale is fixed directly or indirectly, and the expansion and contraction characteristics are different from those of the main scale. At least two calibration marks arranged at intervals, and a calibration sensor attached to the detection head for detecting a change in the interval between the calibration marks are provided, and the calibration sensor detects the calibration marks. The above object is also achieved by using a member to which the main scale is directly or indirectly fixed by correcting the measurement value by the displacement detection signal according to the amount of change in the interval.

[Action and effect]

In the linear displacement detector as described above, the present invention can be expanded and contracted substantially parallel to the main scale 14 (the frame body 15 in which the main scale 14 is housed), as in the example shown in FIG. 1 or 5. A calibration gauge 30 having a desired expansion and contraction characteristic different from that of the main scale is attached, or the main scale 14 (the frame 15 accommodating the same) is fixed as in the example shown in FIG.
At least two calibration marks 44 are provided at predetermined intervals in the longitudinal direction of the main scale on a member having a desired expansion / contraction characteristic different from that of the main scale (for example, the bed 40 of the machine tool).
Meanwhile, the calibration gauge 30 is attached to the detection head 24.
A calibration sensor 32 is attached to detect a change in the interval between the predetermined positions (sensor mark 30A) or the interval between the calibration marks 44, and the amount of change in the interval detected by the calibration sensor 32. The measured value by the displacement detection signal is corrected according to the above. Therefore, it is quick and easy without using an expensive and precise reference device such as a check master or a laser measuring device, or arranging a calibration tool on the bed or table of the machine tool for each calibration work. It is possible to calibrate the system and improve the system accuracy. The calibration cycle needs to be determined by looking at the fluctuation state of the system accuracy, but the shorter the cycle, the higher the system accuracy.

Embodiments of the present invention will be described in detail below with reference to the drawings. In the first embodiment of the present invention, as shown in FIGS. 1 and 2, a frame 15 accommodating a main scale 14 (not shown) fixed to one member that moves relatively, and the other that moves relatively In a linear displacement measuring instrument for electrically measuring the relative displacement between both members by a displacement detection signal obtained by a displacement detection sensor of the detection head 24. , A gap between the calibration gauge 30 attached to the frame body 15 substantially parallel to the main scale in a stretchable state, and a sensor mark 30A arranged at a predetermined position on the calibration gauge 30. Of the mark 30A detected by the calibration sensor 36, and a calibration sensor 32 attached to the detection head 24 for detecting a change in
The measured value by the displacement detection signal is linearly corrected according to the amount of change in the interval. The frame body 15 is made of, for example, aluminum, and the main scale 14 made of, for example, glass is fixed therein. In this case, since the glass and aluminum have different linear expansion coefficients, an error due to the difference becomes a problem, but this embodiment corrects them. The calibration gauge 30 is made of, for example, iron, or the same material as the machine tool main body, or the same material as the work, and can be expanded and contracted substantially parallel to the main scale by a fixing screw 34 provided at the center thereof. It is attached to the frame body 15 in such a state. A leaf spring 36 is interposed between the calibration gauge 30 and the frame 15 as shown in FIG. As the calibration sensor 32, for example, a magnetic sensor can be used. The operation of the first embodiment will be described below. In this embodiment, the output signal obtained from the calibration sensor 32 is, for example, as shown in FIG. 3 (A). By pulsing the output signal, a signal as shown in FIG. 3 (B) is obtained. Is obtained. Therefore, for example, when the dimension between the marks 30A on the calibration gauge 30 is 500 mm, the measured value of the linear displacement detector is set to zero on the left side as shown in FIG. 3 (C). On the right side, when the value is 500.045 on the right side, the correction coefficient β for forcibly adjusting the measured value to 500 is obtained as shown in the following equation. 500.045 × β = 500 (2) This β = 0.99991 can be automatically obtained, and after calibration, the measured value is multiplied by β to obtain the displayed value. The correction according to the present embodiment as described above is a linear correction as shown by the solid line A in FIG. 4, and is particularly effective when the total error of the system is linear. However, by providing three or more marks 30A on the calibration gauge 30 and measuring the distance between the marks, the broken line B in FIG.
It is also possible to perform correction by the polygonal line as shown in. Next, a second embodiment of this embodiment will be described in detail with reference to FIG. The second embodiment is the same as the first embodiment, except that the calibration gauge 30 is fixed not to the frame 15 but to the side surface of the bed 40 of the machine tool. In the figure, 42 is a fixing screw for attaching the frame body 15 to the bed 40. The rest of the configuration and operation are the same as in the first embodiment, so description will be omitted. In both the first and second embodiments, since the calibration gauge 30 is provided in the linear displacement measuring device, it can be easily attached to the machine tool. Next, a third embodiment of the present invention will be described in detail with reference to FIGS. 6 and 7. In this embodiment, in the linear displacement measuring device similar to the first embodiment, the main scale longitudinal direction is set on the side surface of the bed 40 of the machine tool to which the frame 15 accommodating the main scale 14 (not shown) is fixed. Two calibration marks at predetermined intervals
44 is arranged. The other machines and functions are the same as those in the first embodiment, and thus the description thereof will be omitted. According to this embodiment, it is possible to correct the system error based on the expansion and contraction of the machine tool having a large heat capacity. Further, in the present embodiment, since the calibration mark 44 is directly attached to the bed 40 of the machine tool, a separate calibration gauge is unnecessary. Further, in this embodiment, since the calibration mark 44 is attached to the side surface of the bed 40 of the machine tool, it is not necessary to process it on the upper surface, and the attachment of the calibration mark 44 is relatively easy. In the embodiment, the present invention is applied to the reflection type photoelectric linear displacement detector, but the applicable range of the present invention is not limited to this, and the transmission type linear displacement detector, magnetic type, etc. It is obvious that the present invention can be applied to other types of linear displacement detectors as well.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a first embodiment of a linear displacement measuring device according to the present invention, FIG. 2 is a plan view showing a state in which a detection head is also removed, and FIG. 3 is a first embodiment. FIG. 4 is a diagram for explaining the calibration method in the example, FIG. 4 is a diagram showing the same correction method, FIG. 5 is a perspective view showing a second embodiment of the present invention, and FIG. 6 is a diagram showing the present invention. 3 is a perspective view showing a third embodiment, FIG. 7 is a side view of the same, FIG. 8 is a sectional view showing an example of the configuration of a conventional reflection type photoelectric displacement detector, and FIG. 9 is a conventional NC device. It is a diagram showing a method of pitch error correction used. 14 ... Main scale, 15 ... Frame, 24 ... Detection head, 30 ...
Calibration gauge, 30A… mark for sensor, 32… calibration sensor, 40… bed, 44… calibration mark.

Claims (2)

(57) [Claims] 1. Displacement obtained by a displacement detecting sensor of a main scale fixed to one member that relatively moves, and a detection head fixed to the other member that relatively moves. In a linear displacement detector that electrically measures the relative displacement between both members by a detection signal, the expansion and contraction characteristics are different from those of the main scale, which is mounted substantially parallel to the main scale and is expandable and contractible. A calibration gauge having characteristics and a calibration sensor attached to the detection head for detecting a change in the spacing at a predetermined position on the calibration gauge, and the spacing detected by the calibration sensor. A linear displacement detector, which corrects a measurement value based on the displacement detection signal in accordance with the change amount of 2. A displacement obtained by a displacement detection sensor of the detection head, comprising a main scale fixed to one of the relative moving members and a detection head fixed to the other of the relative moving members. In a linear displacement detector that electrically measures relative displacement between both members by a detection signal, the main scale is fixed directly or indirectly, the member having different expansion and contraction characteristics from the main scale, and a desired expansion and contraction characteristic At least two calibration marks arranged at a predetermined interval in the longitudinal direction of the main scale, and a calibration sensor attached to the detection head for detecting a change in the intervals between the calibration marks. A linear displacement detector, which corrects a measurement value based on the displacement detection signal according to the amount of change in the interval detected by the calibration sensor.