Displacement measuring device

Abstract

A displacement measuring device capable of use in a vacuum environment is provided. The displacement measuring device includes a scale and a detection head portion arranged to be displaceable relative to the scale and to face the scale with a predetermined gap. The detection head portion detects displacement or position relative to the scale. The scale is arranged in a vacuum. The detection head portion is housed in a housing holder separating an atmospheric environment side from a vacuum environment side. The housing holder includes a relay device for transmitting a detection signal between the detection head portion and the scale in the gap between the detection head portion and the scale.

Description

[0001] Cross-reference to related applications

[0002] This application is based on and claims the priority of Japanese Patent Application No. 2021-018626 (DAS code E73F), filed on February 8, 2021, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a displacement measuring device, and more particularly to a displacement measuring device that can be used in a vacuum environment. Background Technology

[0004] Encoders (displacement measuring devices) are widely used as position detectors for position control of machine components. If the machine component whose position needs to be controlled is installed in a vacuum environment, the encoder (displacement measuring device) is also used in a vacuum environment.

[0005] Reference List

[0006] Patent documents

[0007] Patent Document 1: JP 2020-193929 A

[0008] Patent Document 2: JP 2011-59055A

[0009] Patent Document 3: JP 5286584 B Summary of the Invention

[0010] However, the following problems exist when existing encoders (displacement measurement devices) are set up in a vacuum.

[0011] Since encoders may not have a vacuum-compatible structure, degassing can occur from the resin parts or adhesives used in the encoder, raising concerns that this gas may affect the vacuum level.

[0012] If all parts (materials) of the encoder were to be changed to be vacuum compatible, a redesign and empirical study would be required to achieve a level of measurement accuracy comparable to existing encoders, which would require considerable cost, labor, and time.

[0013] Therefore, a vacuum-compatible displacement measurement device is needed, with performance levels comparable to existing encoders, without increasing costs.

[0014] A displacement measuring device according to an exemplary embodiment of the present invention includes:

[0015] ruler; and

[0016] The detection head is configured to be displaceable relative to the scale and face the scale with a predetermined gap, and is configured to detect displacement or position relative to the scale, wherein...

[0017] The scale is set in a vacuum.

[0018] The detection head is positioned in the atmosphere.

[0019] The detection head is housed in a housing that separates the atmospheric environment side from the vacuum environment side, and

[0020] The housing retainer includes a relay device in the gap between the detection head portion and the scale for transmitting detection signals between the detection head portion and the scale.

[0021] In an exemplary embodiment of the present invention, preferably, the displacement measuring device is a photoelectric encoder, and the relay device is a light-transmitting window.

[0022] In an exemplary embodiment of the present invention, preferably, the detection head portion has a telecentric optical system.

[0023] In an exemplary embodiment of the present invention, preferably, the scale has a pseudo-random pattern.

[0024] In an exemplary embodiment of the present invention, preferably, the ruler is a glass ruler.

[0025] In an exemplary embodiment of the present invention, preferably, the displacement measuring device is an electrostatic capacitive encoder, and the relay device is a dielectric or a separate conductor.

[0026] In an exemplary embodiment of the present invention, preferably, the displacement measuring device is an electromagnetic induction encoder, and the relay device is a dielectric or conductor in addition to a magnetic material.

[0027] A method for installing a displacement measuring device according to an exemplary embodiment of the present invention, the method comprising:

[0028] Set the scale in a vacuum environment;

[0029] The detection head is housed within a housing that separates the atmospheric environment side from the vacuum environment side; and

[0030] The housing retainer assembly that houses the detection head is configured to face the scale with a predetermined gap. Attached Figure Description

[0031] Figure 1 This is an external perspective view of the displacement measuring device according to the first exemplary embodiment;

[0032] Figure 2 This is a schematic diagram showing a portion of a displacement measuring device;

[0033] Figure 3 This is an exploded perspective view of the housing retainer; and

[0034] Figure 4 This is a diagram showing the housing retainer as viewed from the bottom (base) side. Detailed Implementation

[0035] Exemplary embodiments of the invention are illustrated and described with reference to the accompanying drawings following the elements in the figures.

[0036] (First exemplary embodiment)

[0037] Figure 1 This is an external perspective view of the displacement measuring device 100 according to a first exemplary embodiment of the present invention.

[0038] The displacement measuring device 100 according to this embodiment can be used in a vacuum environment.

[0039] Note that the entire displacement measuring device 100 is not set in a vacuum, and the scale 200 is set in a vacuum environment, while the detection head portion 300 is set in an atmospheric environment. In other words, when assuming that one of two machine components moving relative to each other is in a vacuum environment, while the other machine component is in an atmospheric environment, the scale 200 is defined as said one machine component, and the detection head portion 300 is said another machine component.

[0040] This is because the detection head portion 300 is positioned in the atmospheric environment to be separated from the vacuum, since the detection head portion 300 contains gas-generating factors, such as resin components and adhesives.

[0041] The following description uses a reflective photoelectric encoder as an example to illustrate this embodiment.

[0042] The displacement measuring device 100 includes a scale 200, a detection head portion 300, and a housing retainer 400.

[0043] The scale 200 includes a scale substrate 210 having an elongated flat plate shape, and a scale pattern disposed along the positioning direction (longitudinal direction) of the scale substrate 210.

[0044] In this specification, the scale substrate 210 is a glass substrate. The scale 200 is set by, for example, being pressed down by a plurality of leaf springs 211.

[0045] The ruler pattern is formed by arranging bright and dark areas, i.e., reflective and translucent areas, in a predetermined manner. Multiple (two or more) tracks 221 and 222 are provided as the ruler pattern. In this specification, the ruler pattern has two tracks 221 and 222, and the first ruler pattern track 221 is a pseudo-random pattern.

[0046] When extracting a predetermined length portion, the pseudo-random pattern has only one pattern for that portion within the measurement range, and pattern matching can determine the position of that portion on scale 200. That is, the first scale pattern track 221 is used for absolute position measurement. Furthermore, the pseudo-random pattern is highly robust because if the reading range of the detection head portion 300 is set wide enough to have redundancy, some errors in the reading pattern can be corrected. However, the pseudo-random pattern is not highly responsive because pattern matching calculation processing takes some time.

[0047] The second scale pattern track 222 is a periodic pattern in which bright and dark areas repeat at predetermined intervals. The second scale pattern track 222 is a so-called incremental track, which has high responsiveness, but can lead to measurement errors if the pattern is erroneously detected due to changes in light intensity (signal intensity).

[0048] The detection head 300 reads the scale pattern of the scale 200 to detect displacement or position relative to the scale 200.

[0049] The detection head portion 300 is configured to be relatively displaceable in the positioning direction (longitudinal direction) of the scale 200 and to face the scale 200 with a predetermined gap.

[0050] Figure 2 This is a schematic diagram showing a portion of the displacement measuring device 100.

[0051] The detection head part 300 includes a light source part, a lens optical system (310 and 320), a receiving part 330, and a housing 340.

[0052] The light source section includes two light sources (LEDs), and the first light source for the first track 221 and the second light source for the second track 222 are arranged in parallel.

[0053] Note that in Figure 2 The light source is omitted. The direction of the light (detection signal) from the light source is changed by reflection by a mirror (partial mirror), etc., so that the light is introduced into the lens optical system.

[0054] As a lens optical system, a bilateral telecentric optical system is adopted.

[0055] The lens optical system includes an objective lens unit 310 and an imaging lens unit 320. The objective lens unit 310 illuminates the scale 200 with light from the light source portion. The imaging lens unit 320 converges the reflected light from the scale 200 toward the receiving portion 330.

[0056] The objective lens unit 310 and the imaging lens unit 320 each have a structure (lens array) in which the lens for the first track 221 and the lens for the second track 222 are arranged in parallel. Then, the light source part (not shown) is disposed at the focal point of the objective lens unit 310.

[0057] Therefore, the light emitted from the light source passes through the objective lens unit 310 and is applied as parallel light onto the scale 200. Consequently, the gap between the detection head portion 300 and the scale 200 can be relatively widened.

[0058] Furthermore, the tolerance for assembly errors during encoder installation can be increased. In other words, when installing the encoder, the gap between the detection head portion 300 and the scale 200 only needs to be within a certain allowable range, even if it widens slightly from a specific value. Additionally, the tolerance for variation in the gap between the detection head portion 300 and the scale 200 can be increased.

[0059] The receiving section 330 is equipped with a photodetector that performs photoelectric conversion. The photodetector is, for example, a photodetector array or a (one-dimensional or two-dimensional) CCD (CMOS) camera.

[0060] Figure 3 This is an exploded perspective view of the housing retainer 400.

[0061] The housing retainer 400 houses the detection head portion 300 and separates the atmospheric environment side from the vacuum environment side.

[0062] The housing retainer 400 includes a retainer frame portion 410 and a retainer base portion 450.

[0063] The retainer frame portion 410 has a cylindrical shape and securely holds the detection head portion 300 within the cylindrical hole 420. The retainer frame portion 410 has a low-height quadrangular prism shape that includes the cylindrical hole 420.

[0064] For ease of explanation, when the assumption is based on Figure 3 When defining the up / down direction of the housing retainer 400, the upper end face of the retainer frame portion 410 is the open side connected to the atmospheric environment.

[0065] The lower end face of the retainer frame portion 410 is a sealed side that is hermetically sealed by the retainer base portion 450.

[0066] A flat flange portion 411 is provided on the upper end face of the retainer frame portion 410. For example, the flange portion 411 is used to connect to a conduit for leading out wiring. The conduit is used to lead out the signal line 350 of the detection head portion 300.

[0067] The flange portion 411 is provided with a shallow groove 412 surrounding the cylindrical hole 420, and an O-ring (sealant or filler) 413 is inserted into the shallow groove 412.

[0068] On the upper end face of the retainer frame portion 410, the detector retainer plate (detector retainer portion) 421 is configured to protrude into the cylindrical hole 420.

[0069] Two detector holding plates 421 are positioned diagonally opposite each other in the cylindrical hole 420.

[0070] The detection head portion 300 is inserted into the cylindrical hole 420 from below the retainer frame portion 410, and then the detection head portion 300 is fixed to the detector retainer plate 421 with a fixing screw 422.

[0071] The retainer base portion 450 is securely attached to the lower end face of the retainer frame portion 410 by retaining screws 452. An O-ring (sealant or filler) 451 is inserted between the retainer base portion 450 and the retainer frame portion 410. Each retaining screw 452 is provided with a hole for venting.

[0072] On the upper surface side of the holder base portion 450, there is a recessed portion corresponding to the detection head portion 300.

[0073] The holder base portion 450 includes a window portion (relay device) 460 for transmitting light between the detection head portion 300 and the scale 200.

[0074] Figure 4 This is a view of the housing retainer 400 as viewed from the bottom (bottom) side.

[0075] The holder base portion 450 is provided with a hole, and the glass plate 461 is attached to the hole to form a window portion 460, which transmits light while maintaining airtightness.

[0076] The glass plate 461 may be fitted with an anti-reflective film.

[0077] Light from the detection head portion 300 is applied to the scale 200 through the window portion 460, and the reflected light from the scale 200 passes through the window portion 460 and returns to the detection head portion 300.

[0078] By utilizing the displacement measuring device 100 according to this embodiment, which has this structure, the following effects can be obtained.

[0079] (1) In this embodiment, the scale 200 is set in a vacuum environment, while the detection head portion 300 is separated from the vacuum and set in an atmospheric environment. Therefore, if gas is generated from the detection head portion 300, the gas from the detection head portion 300 will not affect the vacuum level.

[0080] (2) In order to have the structure described in (1), there is a problem that the gap between the detection head portion 300 and the scale 200 needs to be widened.

[0081] In this respect, in this embodiment, a bilateral telecentric optical system is used as the optical system of the detection head portion 300. Therefore, since parallel light is applied from the detection head portion 300 to the scale 200, the impact of widening or changing gap between the detection head portion 300 and the scale 200 on the accuracy of reading the pattern on the scale 200 can be reduced.

[0082] (3) If the gap between the detection head portion 300 and the scale 200 is widened, and if the window portion 460 is located between the detection head portion 300 and the scale 200, it is worrying that the accuracy of the detection head portion 300 in reading the pattern will be affected to some extent.

[0083] In this respect, in this embodiment, the scale 200 has two tracks 221 and 222 with different types of patterns. Specifically, one is an absolute pseudo-random pattern to ensure robustness, and the other is an incremental pattern to ensure responsiveness. Therefore, the vacuum-compatible displacement measuring device 100 according to this embodiment can maintain the same performance as existing encoders.

[0084] (Revise)

[0085] In the exemplary embodiments described above, the photoelectric encoder is described as an example, but an electrostatic capacitive encoder or an electromagnetic induction encoder can be used as the detection principle of the encoder.

[0086] An electrostatic capacitive encoder has a transmitting terminal and a receiving terminal on the detection head side, and a coupling terminal on the scale side. The capacitance between the terminals (transmitting and receiving terminals) on the detection head side and the coupling terminal on the scale side varies according to the relative displacement between the detection head and the scale.

[0087] In this case, the relay device provided to the holder base portion 450 can be a dielectric.

[0088] For example, the holder base portion 450 may be provided with a hole, and the hole may be provided with a thin dielectric plate.

[0089] Since the potential (electric field) distribution of the transmitting terminal appears directly on the scale 200 side through the dielectric, only one dielectric plate is needed.

[0090] On the other hand, conductors can be used as relays, but in this case the conductors need to be divided into small pieces.

[0091] For example, if the wide conductor plate is located between the terminals (transmitting and receiving terminals) on the detection head side and the coupling terminals on the scale side, the potential distribution of the transmitting terminals cannot be transmitted to the scale, and the transmitting and receiving terminals cannot be coupled together to a conductor that serves as a relay device.

[0092] In other words, when a conductor is used as a relay device, the relay conductor used for the transmitting terminal is required to be separate from the relay conductor used for the receiving terminal, and the relay conductor used for the transmitting terminal is separated from the transmitting terminal by the same spacing.

[0093] The electromagnetic induction encoder has a transmitting coil (excitation coil) and a receiving coil (detection coil) on the detection head side, and a coupling coil on the scale side. The electromagnetic coupling (electromotive force current generated by the electromagnetic coupling) between the coils (transmitting coil and receiving coil) on the detection head side and the coupling coil on the scale side varies according to the relative displacement between the detection head and the scale.

[0094] In this case, in addition to magnetic materials, the relay device provided to the holder base portion 450 can be a dielectric or a conductor.

[0095] Note that the present invention is not limited to the exemplary embodiments described above, and appropriate modifications may be made without departing from the scope.

[0096] In the above exemplary embodiment, a bilateral telecentric optical system is used, but a single-sided telecentric optical system in which only the object side is a telecentric optical system can also be used.

[0097] List of reference numerals

[0098] 100 Displacement Measurement Equipment

[0099] 200 rulers

[0100] 210 scale substrate

[0101] Orbits 221 and 222

[0102] 300 Detection Head Section

[0103] 310 objective lens units

[0104] 320 Imaging Lens Unit

[0105] 330 Receiving Section

[0106] 340 casing

[0107] 400 Housing Retainer

[0108] 410 Retainer frame section

[0109] 411 Flange portion

[0110] 412 Shallow trough

[0111] 413 O-ring

[0112] 420 Cylindrical Hole

[0113] 421 Detector Holding Plate

[0114] 450 Retainer base section

[0115] 452 Fixing Screw

[0116] 460 window section

[0117] 461 Glass Plate

Claims

1. A displacement measuring device, comprising: A ruler, which has a ruler pattern along the positioning direction; as well as The detection head is configured to be displaceable relative to the scale along the positioning direction and face the scale with a predetermined gap, and is configured to detect displacement or position relative to the scale, wherein... The scale is set in a vacuum. The detection head is positioned in the atmosphere. The detection head is housed in a housing that separates the atmospheric environment side from the vacuum environment side, and The housing retainer includes a relay device disposed in a predetermined gap between the detection head portion and the scale, the relay device transmitting detection signals between the detection head portion and the scale.

2. The displacement measuring device according to claim 1, wherein, The displacement measuring device is a photoelectric encoder, and The relay device is a light-transmitting window.

3. The displacement measuring device according to claim 2, wherein, The detection head portion has a telecentric optical system.

4. The displacement measuring device according to claim 2, wherein, The scale has a pseudo-random pattern.

5. The displacement measuring device according to claim 1, wherein, The ruler is a glass ruler.

6. The displacement measuring device according to claim 1, wherein, The displacement measuring device is an electrostatic capacitive encoder, and The relay device is a dielectric or a separate conductor.

7. The displacement measuring device according to claim 1, wherein, The displacement measuring device is an electromagnetic induction encoder, and Apart from magnetic materials, the relay device is a dielectric or a conductor.

8. A method for installing the displacement measuring device according to claim 1, the method comprising: Set the scale in a vacuum environment; The detection head is housed in a housing retainer that separates the atmospheric environment side from the vacuum environment side; as well as The housing retainer assembly that houses the detection head is configured to face the scale with a predetermined gap.

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