GB2160977A

GB2160977A - Linear scale device

Info

Publication number: GB2160977A
Application number: GB08512782A
Authority: GB
Inventors: Kenji Indo; Yoshihiko Ishimaru; Hiroshi Yamakawa
Original assignee: Sokkisha Co Ltd
Current assignee: Sokkisha Co Ltd
Priority date: 1984-05-29
Filing date: 1985-05-21
Publication date: 1986-01-02
Also published as: JPS60191908U; GB2160977B; DE3518920A1; GB8512782D0

Abstract

A linear scale is disclosed in which the detection head (11) is moved in relation to a reference scale (12) by a carriage (13). A flat output cable (14) is formed of a flexible printed cable which moves within the movement range of the detection head (11). This flat output cable (14) is housed inside a case (10) and is constructed to transmit a detection signal output in response to movement of the detection head (11, 41) to an external output connector (16) which is connected to an external apparatus. <IMAGE>

Description

SPECIFICATION Linear scale device The present invention relates to a linear scale for reading out graduations on the surface of a scale using a detection head and detecting the displacement of the detection head in relation to the scale.

Linear scales have been used as instruments for measuring position or length for machine tools and various different types of measuring instruments. Both magnetic type linear scales and optical type linear scales are known in the prior art. Optical scales have lines engraved in the surface of a glass or metal plate at a constant pitch. This glass or metal plate is the reference scale. The detection head comprising a photoelectric sensor reads out the graduation pattern engraved on the reference scale to detect the displacement (amount of movement) of the detection head in relation to the reference scale.

With the magnetic type of linear scale, a magnetic graduation pattern of sinusoidal or square waves of a constant length are provided on the surface of a rod-shaped magnetic material. This rod-shaped magnetic material constitutes the reference scale. A detection head, which is a magnetic flux response type reproduction head, reads out the magnetic graduations recorded on the reference scale to detect the displacement (amount of movement) of the magnetic head in relation to the reference scale.

Linear scales, whether of the optical or magnetic types, have a detection head which moves relative to a reference scale, output a detection signal (electrical signal) corresponding to the displacement of the detection head.

These detection signals are output to an external section via an output cable connected to the detection head.

When this kind of linear scale is attached to a machine tool, for example, it is necessary that space be provided on the machine tool for the movement of this output cable, which moves with the detection head to which it is connected. One problem that arises is that this output cable may touch parts of the machine tool and be damaged.

An object of the present invention is to provide a linear scale with which, when the device is attached to a machine tool, etc., the space required for the movement of the output cable connected to the detection head can be eliminated and the entire attachment space can be reduced. Another object of the invention is to provided a linear scale which can prevent the output cable connected to the detection head from touching parts of the machine and being damaged.

The linear scale of this invention comprises the following: a scale on the surface of which a graduation pattern is formed; a case equipped with a support which fixedly supports both ends of this scale; detecting means, which moves relative to the scale, detects the graduation pattern on the scale, and generates detection signals corresponding to the displacement of the detection means in relation to the scale; an external output connecter attached to one end of the case for outputting to the outside the detection signal output from the detecting means; carriage means which has a guide section parallel to the scale for guiding and moving the detecting means relative to the scale; and a flat output cable connected between the detecting means and the external output connector, for transmitting the detection signal output from the detecting means to the external output connector, and housed in said case so as to move flexibly in response to the movement and within the movement range of the detecting means and to maintain a state of contact between the detecting means and the external output connector.

The present invention can be better understood with reference to the following drawings in which: Figure 1 is a front cross section of the linear scale according to the first embodiment of the present invention; Figure 2 is a partial perspective of the above embodiment of the invention; Figure 3A is a partial front cross section of the above embodiment; Figure 3B is a partial side cross section of the above embodiment; Figure 4 is perspective of the linear scale device according to a second embodiment of the invention; and Figure 5 is a cross section of the detection head and its surrounding according to the second embodiment of the invention.

The following is a description with reference to Figs. 1 to 3B of the first embodiment of the present invention. Fig. 1 is a front cross section of the linear scale which is provided with case 10, detection head 11, magnetic scale 12, carriage 13, flat output cable 14, amplifier 1 5 and external output connector 1 6. Magnetic scale 1 2 is formed of a rodshaped magnetic material and has magnetic grid-shaped graduations of constant-length magnetic sinusoidal or square waves formed on the surface.Magnetic scale 1 2 is supported at both ends by supports 1 7a, 1 7b and housed in case 1 0. Detection head 11, which comprises a reproduction head that is responsive to magnetic flux, is coaxial with magnetic scale 1 2. Detection head 11 is fastened to carriage 1 3 and moves relative to magnetic scale 12. Detection head 11 reads out the magnetic graduation pattern formed on magnetic scale 1 2 and converts the pattern into electrical signals (detection signals) for output.

Flat output cable 14 is attached at one end to carriage 1 3 and at the other end to amplifier 1 5. The end of flat output cable 14 attached to carriage 1 3 is attached to output line 20 of detection head 11 via connection plate 21, as shown in Fig. 2. This end of flat output cable 14 is held by a thin metal guide plate 22 attached to carriage 13, and is guided in a direction parallel to magnetic scale 1 2. Flat output cable 14 is a flexible printed cable having a plurality of conductive wires printed on a flexible base such as Polymid or Mylar (trademarks of Dupont). The detection signals output from detection head 11 are transmitted via this flat output cable 14 to amplifier 1 5.

After amplifying this detection signal, amplifier 1 5 outputs the signal to external output connector 16, which is connected to external output line 18, as shown in Fig. 1. The detection signal from amplifier 1 5 is supplied via external output line 18 to an external device such as a machine tool (not shown).

Carriage 13, as shown in Fig. 3A, is constructed to slide on bearings 31 along guide rail 30 which is placed parallel to magnetic scale 1 2. Carriage 1 3 sliding along guide rail 30 results in detection head 11, which is attached to carriage 13, moving relative to magnetic scale 12, as is shown in Fig. 3B (side cross section). Operation section 32 is attached to carriage 13, and, when operated from the outside, moves carriage 1 3 parallel to magnetic scale 1 2.

With a linear scale such as that described above, the linear scale is fastened to a prescribed location to on the machine tool for position detection by the positioning control section of the machine tool. When the table of the machine tool moves, for example, carriage 1 3 moves in a prescribed direction in response to the movement of the table. The movement of carriage 1 3 results in detection head 11 moving along magnetic scale 1 2.

Detection head 11 reads the magnetic graduation pattern recorded on magnetic scale 12, and, after conversion of the graduation pattern into electrical detection signals, it outputs the signals to output line 20 shown in Fig. 2.

The detection signal output from detection head 11 to output line 20 is transmitted by flat output cable 14 to amplifier 15, and, after amplification, is output to the positioning control section of the machine tool via external output connector 1 6 and external output line 1 8. The machine tool positioning control section detects the displacement (amount of movement) of detection head 11 based on the transmitted detection signal to determine the position of the machine tool table.

When detection head 11 moves in response to the movement of carriage 13, flat output cable 14 attached to carriage 1 3 also moves inside case 1 0. Flat output cable 14 is a flexible printed cable provided attached to guide plate 22 of carriage 1 3 parallel to the direction of movement of detection head 11.

Consequently, in response to the movement of detection head, cable 14 moves flexibly in case 10 in relation to the direction of movement of detection head 11. So, detection head 11 moves within a range corresponding to the length of magnetic scale 1 2 and the detection signal from detection head 11 is reliably sent to a amplifier 1 5 via flat cable 14. Since flat cable 14 moves inside case 10 within the movement range of detection head 11, when the linear scale is attached to a machine tool, etc., there is no possibility of cable 14 coming into contact with parts of the machine tool, which, accordingly, prevents the cable from being damaged.This decrease in the danger of damage means that the detection signal can be sent with great reliability to external output connector 1 6 via amplifier 1 5. The life of flat cable 14 is also greatly increased. It is also unnecessary to provide a special space for the movement of the cable, which simplifies the design of the linear scale attachment section of the machine tool.

Figs. 4 and 5 show a second embodiment of the invention. In this case the linear scale is an optical type having as the reference scale a scale 40 which is made of a glass plate, for example, instead of the magnetic plate of the first embodiment, and a detection head 41, which comprises a photoelectric sensor. Scale 40 has etched constant-pitch lines 42 of a graduation pattern formed on its surface.

Detection head 41 is attached to carriage 1 3 such that with the movement of carriage 1 3 detection head 41 moves relative to scale 40. Detection head 41 has a light emitter 43a, such as a light emitting diode, and a light receptor 43b such as a phototransistor, as shown in Fig. 5 (side cross section). Light emitter 43a and light receptor 43b are placed on either side of scale 40 in opposing directions.

The rest of the construction of this optical linear scale is the same as that of the magnetic scale shown in Fig. 1. Namely, scale 40 is fixedly supported by supports inside the case and flat output cable 1 4 is connected at one end to carriage 1 3 and at the other end to amplifier 1 5. The detection signal from detection head 41 is amplified and supplied to external output connector, which is connected to the external apparatus. Carriage 1 3 of the optical scale has the same structure as that shown in Fig. 3A.

When the light emitted from light emitter 43a of detection head 41 is interrupted by an engraved line 42 on scale 40, an electrical detection signal of the graduation pattern from light receptor 43b is output to flat output cable 14 via output line 44a.

This kind of optical linear scale is able to obtain the same operational effects as the magnetic linear scale of the first embodiment.

Namely, when detection head 41 moves, flat output cable 14 moves flexibly inside the case. Accordingly, the flat output cable is prevented from contacting parts of the machine tool to which the linear scale is attached, thereby preventing damage to the cable. There is also no need to specially provide space for the cable movement so the space required for attachment to the machine tool can be drastically reduced.

Claims

1. A linear scale device comprising: a scale on the surface of which a graduation pattern is formed; a case equipped with a support which fixedly supports both ends of said scale; detecting means, which moves relative to said scale, detects the graduation pattern on said scale, and generates detection signals corresponding to the displacement of said detection means in relation to said scale; an external output connector attached to one end of said case for outputting to the outside the detection signal output from said detecting means; carriage means which has a guide section parallel to said scale for guiding and moving said detecting means relative to said scale; and a flat output cable connected between said detecting means and said external output connector, for transmitting the detection signal output from said detecting means to said external output connector, and housed in said case so as to move flexibly in response to the movement and within the movement range of said detecting means and to maintain a state of contact between said detecting means and said external output connector.

2. A linear scale device according to claim 1, wherein a magnetic graduation pattern is recorded on a surface of said scale and said detecting means comprises a reproduction head responsive to magnetic flux for reading out the magnetic graduation pattern from said scale and outputting a detection signal in response to a displacement of said detecting means.

3. A linear scale device according to claim 1, wherein lines are engraved at equal intervals on a surface of said scale and said detecting means comprises a photoelectric sensor for detecting the engraved lines on said scale and outputting a detection signal corresponding to a displacement of said detecting means.

4. A linear scale device according to claim 1, wherein said flat output cable is a flexible printed cable constructed by printing conductive wires on a base of flexible material.

5. A linear scale device according to claim 2, wherein said scale is a rod-shaped magnetic medium and said detecting means comprises a reproduction head which moves coaxially with said scale and is responsive to magnetic flux.

6. A linear scale device according to claim 3, wherein said scale comprises a glass plate on a surface of which lines are engraved and said detecting means comprises a photoelectric sensor having a light emitting section and light receiving section placed opposing each other with said scale in between.

7. A linear scale device according to claim 4, wherein one end of said flat output cable is held parallel to the direction of movement of said detecting means by a guide plate, which is attached to said carriage means.

8. A linear scale device, substantially as hereinbefore described with reference to the accompanying drawings.