Encoder

Abstract

An encoder according to the present disclosure is provided with a pedestal, a circuit board, a cover, a connector, and a grounding member. The pedestal is conductive. The circuit board is placed on the pedestal. The cover is insulating, is placed on the pedestal, and is of a size to cover the circuit board. The connector is used to connect or disconnect an external cable and is mounted to the cover. The grounding member is run between the connector and the pedestal. In the encoder according to the present disclosure, the grounding member has a structure that exhibits elasticity.

Description

Encoder

[0001] The present disclosure relates to encoders.

[0002] With the evolution of electronic components, many high-precision electronic components are mounted on circuit boards, and the effects of electromagnetic noise from components mounted around the circuit board and cables surrounding the circuit board can no longer be ignored. For this reason, various electromagnetic noise countermeasures have been proposed for individual components (see, for example, Patent Document 1). Encoders mounted on motors and other devices are no exception. Electromagnetic noise emitted from circuit boards that detect the rotational angle position of the motor can cause the encoders to malfunction, and in the worst case, can even cause them to fail.

[0003] Japanese Patent Application Laid-Open No. 2018-181404

[0004] In electronic components such as encoders that have circuit boards, noise countermeasures for the circuit boards are desired.

[0005] The encoder according to the present disclosure includes a conductive base, a circuit board mounted on the base, an insulating cover arranged on the base and covering the circuit board, a connector attached to the cover for connecting and disconnecting an external cable, and a ground member bridged between the connector and the base. The ground member has an elastic structure.

[0006] FIG. 1 is a perspective view showing the appearance of a motor unit including an encoder according to a first embodiment. FIG. 2 is an exploded perspective view of the encoder of FIG. 1. FIG. 3 is a perspective view showing the back side of the cover of FIG. 2. FIG. 4 is a perspective view showing an example of the earth member of FIG. 2. FIG. 5 is a cross-sectional view showing a state in which the earth member is attached to the cover of FIG. 2. FIG. 6 is a cross-sectional view showing a state in which a connector is attached to the cover of FIG. 2. FIG. 7 is a cross-sectional view showing a state in which the cover of FIG. 6 is attached to a base. FIG. 8 is a perspective view showing another example of the earth member of FIG. 2. FIG. 9 is a cross-sectional view showing a state before a connector is attached to the cover in an encoder according to a second embodiment. FIG. 10 is a cross-sectional view showing a state after a connector is attached to the cover in an encoder according to the second embodiment.

[0007] Encoders according to first and second embodiments will be described below with reference to the drawings. In the first embodiment, an example will be described in which an O-ring, which is a sealing member, is sandwiched between a cover and a base, and in the second embodiment, an example will be described in which an O-ring, which is a sealing member, is sandwiched between a cover and a connector. In the following description, components having substantially the same functions and configurations will be given the same reference numerals, and repeated description will be given only when necessary.

[0008] An encoder 2 according to the first embodiment will be described below with reference to Figures 1 to 8. As shown in Figure 1, the encoder 2 according to the first embodiment is attached to a motor housing 90 of the motor 9 so as to measure the rotational angle position and rotational speed of the drive shaft of the motor 9, or the displacement and displacement speed of a linear shaft driven by the motor 9. The encoder 2 according to the first embodiment constitutes a motor unit 1 together with the motor 9.

[0009] As shown in FIG. 2 , the encoder 2 according to the first embodiment includes a conductive base 20 (encoder flange) fixed to a motor housing 90 with conductive screws (not shown) or the like, a circuit board 22 installed on the base 20, an insulating cover 40 detachably attached to the base 20 and covering the circuit board 22, a connector 60 detachably attached to the cover 40, and a conductive earth member (conductive member) 80 bridged between the base 20 and the connector 60. The earth member 80 may be made of copper, which has high conductivity, or conductive silicone rubber or conductive plastic. In the first embodiment, the earth member 80 is referred to as an earth member because it is grounded, but it may also be referred to as a ground member for setting the encoder 2 at a ground potential. In the first embodiment, an O-ring 30 is disposed between the base 20 and the cover 40 as a sealing member. The O-ring 30 is sandwiched between the base 20 and the cover 40 and deformed when the cover 40 is attached to the base 20. In the first embodiment, the O-ring 30 serving as a sealing member is not a component of the encoder 2 , but may be one of the components of the encoder 2 .

[0010] Typically, each component of the encoder 2 is configured as follows. As shown in FIG. 2 , the base 20 is realized by a rectangular metal plate. Screw holes 29 are drilled in each of the four corners of the base 20. A plurality of conductive support posts 21 are erected on the surface of the base 20, and a circuit board 22 is held at the tips of the support posts 21. For example, the circuit board 22 is grounded via the support posts 21 and the base 20. The circuit board 22 and the connector 60 are electrically connected by an internal cable 23.

[0011] The cover 40 has a square box-shaped cover main body 40a large enough to cover the entire circuit board 22 placed on the base 20, and a rectangular annular cover edge 40b that protrudes outward from an end of the cover main body 40a. One side plate of the cover main body 40a has a rectangular socket 41 into which the connector 60 is inserted. Two short cylindrical protrusions 42 are provided, spaced apart from one another, on the left and right sides of the socket 41 on the cover main body 40a.

[0012] The cover edge portion 40b has four corners each having through-holes 49 extending vertically through the cover edge portion 40b for receiving screws. As shown in FIG. 3 , a narrow annular groove 45 for receiving an O-ring 30, a sealing member, is provided on the back surface of the cover edge portion 40b, surrounding the opening of the cover body portion 40a. Two recesses 44 are provided on the back surface of the cover edge portion 40b, outside the groove 45. The two recesses 44 are large enough to accommodate the elastic portion, base contact portion, and folded portion of the grounding member 80 (described below), and are provided at positions corresponding to the left and right sides of the insertion port 41 of the cover body portion 40a. A slit 43 is provided in the bottom surface of each recess 44, penetrating the cover edge portion 40b. The slit 43 has a width equal to or slightly larger than the width of the grounding member 80, allowing the connector contact portion 801 of the grounding member 80 to be inserted therethrough. The earth member 80, which will be described later, is inserted from the back side of the cover 40 into the recess 44 and then the slit 43, and is positioned and fixed to the cover main body 40a by fitting two circular through holes 81 provided in the earth member 80 onto two protrusions 42 of the cover main body 40a, respectively. The earth member 80 fixed to the cover 40 is positioned outside the O-ring 30, which is a sealing member. As a result, the O-ring 30 does not need to be larger than when the earth member 80 fixed to the cover 40 is positioned inside the O-ring 30, and the waterproof performance of the encoder can be improved.

[0013] 2, the connector 60 includes an insulating connector housing 61 having a connection port 62 to which a connector 72 of an external cable 70 is connected, and conductive contacts 63 housed in the connector housing 61 for ensuring electrical connection between the internal cable 23 wired from the circuit board 22 and the external cable 70 wired from an external device. Although not shown, the connector 60 also has a fastening structure for the cover 40. Any known fastening structure can be used as the fastening structure, such as a fitting structure or a screw fastening structure.

[0014] In the encoder 2 according to the first embodiment, the conductive base 20 is grounded. The grounding method is not limited. For example, the conductive base 20 may be grounded directly by a ground wire or the like, or may be grounded indirectly via another conductive member. As shown in FIGS. 1 and 2 , in the first embodiment, a motor housing 90 of a conductive motor 9 is grounded by a ground wire (not shown), and the base 20, which is fastened to the motor housing 90 of the motor 9 by conductive screws (not shown), is grounded via the motor housing 90.

[0015] The encoder 2 according to the first embodiment includes a conductive earth member 80 that is bridged between the connector 60 (contacts) and the base 20 in order to ground the external cable 70 connected to the connector 60 without passing through the internal cable 23 and the circuit board 22. The earth member 80 is attached to the cover 40 that is capable of contacting both the connector 60 and the base 20. In order to stably ground the external cable 70, it is necessary for the earth member 80 to be in reliable contact with the connector 60 and the base 20. On the other hand, in cases where an O-ring 30 is sandwiched between the cover 40 and the base 20 or between the cover 40 and the connector 60, the earth member 80 must not prevent the O-ring 30 from being completely crushed so as not to reduce the waterproof performance of the encoder 2. Therefore, the encoder 2 of the first embodiment has a structure (referred to as an elastic portion) that exhibits elasticity so that the earth member 80 that is stretched between the base 20 and the connector 60 can be in secure contact with the base 20 and the connector 60 while not hindering deformation of the O-ring 30 (crushing of the O-ring 30).

[0016] In the first embodiment, the direction in which the connector 60 is attached to the cover 40 is perpendicular to the direction in which the cover 40 is attached to the base 20. Therefore, the grounding member 80 is configured so that the connector contact portion 801 that comes into contact with the connector 60 and the base contact portion 804 that comes into contact with the base 20 are perpendicular to each other. Furthermore, since the O-ring 30 is sandwiched between the base 20 and the cover 40, the elastic portion of the grounding member 80 is configured to exert elasticity when the cover 40 is attached to the base 20.

[0017] FIG. 4 shows an example of the grounding member 80. As shown in FIG. 4, the grounding member 80 is realized by a metal plate bent into a substantially J-shape. Specifically, the metal plate is bent in the forward direction at three positions 80a, 80b, and 80c, which are spaced apart by a predetermined distance from one end to the other, at 45 degrees, 45 degrees, and 90 degrees, respectively. The portion from one end of the metal plate to a position between the one end of the metal plate and the first bent portion 80a is referred to as a connector contact portion 801. The portion from the position between the one end of the metal plate and the first bent portion 80a (connector contact portion 801) to the first bent portion 80a is referred to as a connection portion 802. The portion including the first bent portion 80a, the second bent portion 80b, and the portions therebetween is referred to as an elastic portion 803. The portion from the second bent portion 80b to the third bent portion 80c is referred to as a base contact portion 804. The portion from the third bent portion 80c to the other end of the metal plate is referred to as a folded portion 805. When a force F1 is applied perpendicular to the base contact portion 804 (the surface of the base 20) while the base contact portion 804 is in contact with the surface of the base 20, the bending angle of the bent portion 80a of the elastic portion 803 widens, and the entire grounding member 80 is deformed so as to bend. The deformed grounding member 80 attempts to return to its original shape. In this way, the two bent portions 80a and 80b between the connector contact portion 801 and the base contact portion 804 function as the elastic portion 803 that exerts elasticity when attaching the cover 40 to the base 20.

[0018] FIG. 5 shows the state in which the grounding member 80 is attached to the cover 40. As shown in FIG. 5( a), the grounding member 80 fixed to the cover 40 has its base contact portion 804 protruding toward the base 20 from a plane S1 that coincides with the back surface of the cover 40. As shown in FIG. 5( b), when the cover 40 is brought closer to the base 20 to attach the cover 40 to the base 20, the base contact portion 804 of the grounding member 80 first comes into contact with the surface of the base 20. From this state, the cover 40 can be pressed against the base 20 with a force that resists the restoring force of the grounding member 80, thereby deforming the grounding member 80 so that the bending angle of the bent portion 80a of the elastic portion 803 increases. When the grounding member 80 is deformed, the elastic portion 803, the base contact portion 804, and the folded portion 805 of the grounding member 80 are accommodated in the recess 44. 5(c), the back surface of the cover 40 can be brought into close contact with the surface of the base 20. The deformed grounding member 80 generates a restoring force Fr for returning to its pre-deformation shape, that is, a state in which the base contact portion 804 protrudes from the plane S1 coinciding with the back surface of the cover 40 toward the base 20. This restoring force Fr presses the base contact portion 804 of the grounding member 80 against the base 20, thereby realizing stable contact of the grounding member 80 with the base 20.

[0019] The effects of the configuration of the encoder 2 according to the first embodiment will be described below with reference to Figures 6 and 7. Figure 6 shows a state in which a connector 60 is attached to a cover 40 to which a grounding member 80 is attached, and an external cable 70 is connected to the connector 60. Figure 7 shows a state in which the cover 40 of Figure 6 is attached to a base 20.

[0020] 6 , when the connector 60 is attached to the cover 40 to which the grounding member 80 is fixed, the grounding member 80 can be brought into contact with the connector 60. Specifically, the connector contact portion 801 of the grounding member 80 can be brought into contact with the contact 63 of the connector 60. When the external cable 70 is attached to the connector 60, the grounding wire 73 of the external cable 70 is electrically connected to the grounding member 80 via the contact 63. Of course, the grounding wire 73 of the external cable 70 may be directly connected to the grounding member 80 via another conductive member.

[0021] As shown in FIG. 7 , the cover 40 shown in FIG. 6 is pressed against the base 20 to be attached to the base 20. As shown in FIG. 6 , the grounding member 80 protrudes toward the base 20 from the back surface of the cover 40. The grounding member 80 has an elastic portion 803 that exerts elasticity in the direction in which the cover 40 is pressed against the base 20. Therefore, by continuing to press the cover 40 against the base 20 with a force that resists the restoring force of the grounding member 80, the grounding member 80 can be deformed, and the back surface of the cover 40 can be closely attached to the surface of the base 20. When the back surface of the cover 40 is closely attached to the surface of the base 20, the grounding member 80 is not interposed between the back surface of the cover 40 and the surface of the base 20. Therefore, the grounding member 80 does not hinder the deformation of the O-ring 30, and the O-ring 30 sandwiched between the cover 40 and the base 20 can be completely crushed. Meanwhile, when the cover 40 is attached to the base 20, the deformed grounding member 80 generates a restoring force that attempts to return to its original shape before deformation. This restoring force presses the base contact portion 804 of the grounding member 80 against the base 20, thereby realizing stable contact of the grounding member 80 with the base 20.

[0022] According to the encoder 2 of the first embodiment, the earth member 80 spanning between the connector 60 and the base 20 has an elastic structure, and by deforming the earth member 80 together with the deformation of the O-ring 30, the cover 40 can be attached to the base 20 without hindering the deformation of the O-ring 30 sandwiched between the cover 40 and the base 20. Furthermore, with the cover 40 attached to the base 20, the earth member 80 generates a restoring force that presses the base contact portion 804 against the base 20, and therefore the earth member 80 can be brought into stable contact with the base 20.

[0023] As described above, the encoder 2 according to the first embodiment can maintain waterproof performance while stabilizing the electrical continuity between the connector 60 and the base 20 via the grounding member 80. As a result, the external cable 70 connected to the connector 60 can be stably grounded to the base 20 via the grounding member 80 without passing through the internal cable 23 and the circuit board 22, suppressing electromagnetic noise that would otherwise be radiated from the internal cable 23 to the circuit board 22 and preventing malfunctions and failures of the circuit board 22.

[0024] While the grounding member 80 has been described with reference to Fig. 4, the shape of the grounding member 80 is not limited to that shown in Fig. 4, as long as the connector contact portion 801 and the base contact portion 804 are perpendicular to each other and the grounding member 80 has a structure that exhibits elasticity in the direction in which the cover 40 is attached to the base 20. Fig. 8 shows another example of the grounding member 80. As shown in Fig. 8, the grounding member 85 is realized by a metal plate that is bent so as to have a folded portion. The metal plate is bent at two positions, spaced a predetermined distance apart, from one end to the other, at 45 degrees forward and 135 degrees backward, respectively. The portion from one end of the metal plate to the position between one end of the metal plate and the first bent portion 85a is called a connector contact portion 851, the portion from the position between one end of the metal plate and the first bent portion 85a to the first bent portion 85a is called a connection portion 852, the portion between the first bent portion 85a and the second bent portion 85b and therebetween is called an elastic portion 853, and the portion from the second bent portion 85b to the other end of the metal plate is called a base contact portion 854. When a force F2 is applied in a direction perpendicular to the base contact portion 854 (the surface of the base 20) with the base contact portion 854 in contact with the surface of the base 20, the bending angle of the first bent portion 85a and the bending angle of the second bent portion 85b of the elastic portion 853 increase, and the grounding member 85 is deformed so that the first bent portion 85a approaches the base contact portion 854, that is, so that the elastic portion 853 contracts. In this way, the two bent portions 85 a and 85 b between the connector contact portion 851 and the base contact portion 854 function as elastic portions 853 that exert elasticity when the cover 40 is attached to the base 20 .

[0025] An encoder 2' according to the second embodiment will be described below with reference to Figures 9 and 10. The encoder 2' according to the second embodiment differs from the encoder 2 according to the first embodiment in the position where the O-ring 30, which is a sealing member, is sandwiched. Therefore, the second embodiment will be described mainly with reference to the differences from the encoder 2 according to the first embodiment.

[0026] As shown in Figure 9, one side plate of the cover main body 40a' has a rectangular socket into which the connector 60 is inserted. Recesses 44' are provided on both the left and right sides of the socket of the cover main body 40a'. These recesses 44' correspond to the recesses 44 provided on the back surface of the cover edge portion 40b of the encoder 2 according to the first embodiment, and are large enough to accommodate the connector contact portion 805' of the grounding member 80'. One side plate of the cover main body 40a' has a narrow, annular groove 45' that surrounds the socket. An O-ring 30', which serves as a sealing member, is fitted into this groove 45'.

[0027] The grounding member 80′ is configured so that a connector contact portion 805′ that comes into contact with the connector 60 and a base contact portion 806′ that comes into contact with the base 20 are perpendicular to each other. In addition, since an O-ring 30′ is sandwiched between the cover 40′ and the connector 60, the elastic portion of the grounding member 80′ is configured to exert elasticity when the connector 60 is attached to the cover 40′.

[0028] The grounding member 80' according to the second embodiment is obtained by bending one end of a metal plate in the opposite direction by 90 degrees in the grounding member 80 of the encoder 2 according to the first embodiment described with reference to Figure 4. The portion of the metal plate from one end to the first bent portion 80d' is referred to as a base contact portion 806', the portion of the metal plate from one end to the second bent portion 80a', the third bent portion 80b', and the portions between them are referred to as an elastic portion 803', and the portion of the metal plate from one end to the fourth bent portion 80c' to the other end of the metal plate. The grounding member 80' is molded integrally with the cover 40', and when the cover 40' is attached to the base 20, the base contact portion 806' of the grounding member 80' comes into contact with the base 20.

[0029] As shown in FIG. 9 , the connector contact portion 805′ of the grounding member 80′ protrudes toward the connector 60 from the surface of the cover 40′. However, the grounding member 80′ has an elastic portion that exerts elasticity in the direction in which the connector 60 is pressed against the cover 40′. Therefore, by continuing to press the connector 60 against the cover 40′ with a force that resists the restoring force of the grounding member 80′, the grounding member 80′ can be deformed, and the surface of the connector 60 can be brought into close contact with the surface of the cover 40′. When the surface of the connector 60 is brought into close contact with the surface of the cover 40′, the grounding member 80′ is not interposed between the surfaces of the cover 40′ and the connector 60. Therefore, the grounding member 80′ does not hinder the deformation of the O-ring 30′, and the O-ring 30′ sandwiched between the cover 40′ and the connector 60 can be completely crushed. Meanwhile, when the connector 60 is attached to the cover 40′, the deformed grounding member 80′ generates a restoring force that attempts to return to its original shape before deformation. This restoring force presses the connector contact portion 805 ′ of the grounding member 80 ′ against the connector 60 , thereby realizing stable contact of the grounding member 80 ′ with the connector 60 .

[0030] According to the encoder 2 of the second embodiment, the earth member 80' bridged between the connector 60 and the base 20 has an elastic structure, which causes the earth member 80' to deform together with the O-ring 30', and allows the connector 60 to be attached to the cover 40' without interfering with the deformation of the O-ring 30' sandwiched between the cover 40' and the connector 60. Furthermore, with the connector 60 attached to the cover 40', the earth member 80' generates a restoring force that presses the connector contact portion 805' against the connector 60, allowing the earth member 80' to come into stable contact with the connector 60.

[0031] As described above, the encoder 2' according to the second embodiment can stabilize the electrical continuity between the connector 60 and the base 20 via the grounding member 80' while maintaining waterproof performance. As a result, the external cable 70 connected to the connector 60 can be stably grounded to the base 20 via the grounding member 80' without passing through the internal cable 23 and the circuit board 22, thereby suppressing electromagnetic noise that would otherwise be radiated from the internal cable 23 to the circuit board 22 and preventing malfunctions and failures of the circuit board 22.

[0032] In the first embodiment, the grounding member 80 has a structure 803 that exerts elasticity when the cover 40 is attached to the base 20, while in the second embodiment, the grounding member 80' has a structure 803' that exerts elasticity when the connector 60 is attached to the cover 40'. Naturally, there may be cases where a sealing member is sandwiched between the cover and the base, and further where a sealing member is sandwiched between the cover and the connector. In such cases, a grounding member having a shape that combines the grounding members of the first and second embodiments may be used. That is, the grounding member is configured to have both a first structure that exerts elasticity when the cover is attached to the base, and a second structure that exerts elasticity when the connector is attached to the cover. In this way, the grounding member has an elastic structure, and its restoring force presses it against at least one of the base and the connector.

[0033] The following supplementary notes are further disclosed regarding this embodiment and its modified examples. (Supplementary Note 1) The encoder 2 includes a conductive base 20, a circuit board 22 installed on the base 20, an insulating cover 40 arranged on the base 20 and covering the circuit board 22, a connector 60 attached to the cover 40 for connecting and disconnecting an external cable 70, and a grounding member 80 bridged between the connector 60 and the base 20. The grounding member 80 has an elastic structure 803 (803'). (Supplementary Note 2) The grounding member 80 of Supplementary Note 1 has an elastic structure 803 that is elastic when the cover 40 is attached to the base 20, and is pressed against the base 20 by its restoring force. (Supplementary Note 3) The grounding member 80' of Supplementary Note 1 has an elastic structure 803' that is elastic when the connector 60 is attached to the cover 40', and is pressed against the connector 60 by its restoring force. (Supplementary Note 4) The earthing member 80 of Supplementary Note 1 has a first structure 803 that exhibits elasticity when the cover 40 is attached to the base 20, and a second structure 803' that exhibits elasticity when the connector 60 is attached to the cover 40', and is pressed against the base 20 by the restoring force of the first structure 803, and is pressed against the connector 60 by the restoring force of the second structure 803'. (Supplementary Note 5) The encoder 2 of Supplementary Note 2 further includes a sealing member 30 that deforms between the base 20 and the cover 40. The earthing member 80 is deformed together with the deformation of the sealing member 30, and is pressed against the base 20 by the restoring force. (Supplementary Note 6) The encoder 2 of Supplementary Note 3 further includes a sealing member 30' that deforms between the connector 60 and the cover 40'. The earthing member 80' is deformed together with the deformation of the sealing member 30', and is pressed against the connector 60 by the restoring force. (Supplementary Note 7) The encoder 2 of Supplementary Note 4 further includes a first sealing member 30 that deforms between the base 20 and the cover 40, and a second sealing member 30' that deforms between the connector 60 and the cover 40'. The grounding member 80 is deformed together with the deformation of the first sealing member 30 and is pressed against the base 20 by its restoring force, and is deformed together with the deformation of the second sealing member 30' and is pressed against the connector 60 by its restoring force.(Supplementary Note 8) In the encoder 2 of Supplementary Note 5 or Supplementary Note 6, the grounding member 80 (80') is arranged outside the sealing member 30 (30'). (Supplementary Note 9) In the encoder 2 of any one of Supplementary Notes 1 to 8, the grounding member 80 has a connector contact portion 801 that contacts the connector 60, a base contact portion 804 that contacts the base 20, and an elastic portion 803 that is interposed between the connector contact portion 801 and the base contact portion 804. (Supplementary Note 10) In the encoder 2 of Supplementary Note 9, the elastic portion 803 has two bent portions 80a, 80b. (Supplementary Note 11) In the encoder 2 described in Supplementary Note 9, the two bent portions 80a, 80b are bent in the same direction. (Supplementary Note 12) In the encoder 2 described in Supplementary Note 9, the two bent portions 85a, 85b are bent in opposite directions.

[0034] Although the embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the invention or the concept and spirit of the present invention derived from the content of the claims and their equivalents. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0035] 1...motor unit, 2...encoder, 20...base, 21...support, 22...circuit board, 23...internal cable, 29...screw hole, 30...sealing member (O-ring), 40...cover, 41...socket, 42...protrusion, 43...slit, 44...depression, 45...groove, 49...through hole, 50...screw, 60...connector, 61...connector housing, 62...connection port, 63...contact, 70...external cable, 72...connector, 73...earth wire, 80...earth member, 81...through hole

Claims

1. An encoder comprising: a conductive base; a circuit board placed on the base; an insulating cover placed on the base and covering the circuit board; a connector attached to the cover for connecting and disconnecting an external cable; and an earth member bridged between the connector and the base, the earth member having an elastic structure.

2. The encoder according to claim 1, wherein the earth member has a structure that exerts elasticity when the cover is attached to the base, and is pressed against the base by its restoring force.

3. The encoder according to claim 1, wherein the earth member has a structure that exerts elasticity when the connector is attached to the cover, and is pressed against the connector by its restoring force.

4. The encoder according to claim 1, wherein the earth member has a first structure that exerts elasticity when the cover is attached to the base, and a second structure that exerts elasticity when the connector is attached to the cover, and is pressed against the base by the restoring force of the first structure, and is pressed against the connector by the restoring force of the second structure.

5. The encoder according to claim 2, further comprising a sealing member which is deformed between the base and the cover, wherein the earth member is deformed together with the deformation of the sealing member and is pressed against the base by its restoring force.

6. The encoder according to claim 3, further comprising a sealing member which is deformed between the connector and the cover, wherein the earth member is deformed together with the deformation of the sealing member and is pressed against the connector by its restoring force.

7. The encoder according to claim 4, further comprising: a first sealing member which deforms between the base and the cover; and a second sealing member which deforms between the connector and the cover, wherein the earth member is deformed together with the deformation of the first sealing member and is pressed against the base by its restoring force, and is deformed together with the deformation of the second sealing member and is pressed against the connector by its restoring force.

8. The encoder according to claim 5 or 6, wherein the earth member is disposed outside the sealing member.

9. An encoder as described in any one of claims 1 to 8, wherein the earth member has a connector contact portion that contacts the connector, a base contact portion that contacts the base, and an elastic portion interposed between the connector contact portion and the base contact portion.

10. The encoder according to claim 9, wherein the elastic portion has two bent portions.

11. The encoder according to claim 10, wherein the two bent portions are bent in the same direction.

12. The encoder according to claim 10, wherein the two bent portions are bent in opposite directions to each other.