Balancer and Robot Systems

Abstract

This balancer (1) is provided with: a housing (2) which, by means of first bearings (21), is rotatably attached to a first member or a second member of a robot so as to be rotatable about a first attachment axis (X) parallel to a rotation axis, wherein said robot is provided with the first member and the second member, which is driven to rotate about the rotation axis with respect to the first member; a rod (3) which, by means of a second bearing (22), is attached at one end to the other of the first member and the second member so as to be rotatable about a second attachment axis (Y) parallel to the rotation axis; a force generating means (5) which generates force in the direction which draws the rod (3) into the housing (2) or the direction which pushes the rod out of the housing (2); and a sensor (6) which detects the positional relation between the housing (2) and the rod (3) in the direction perpendicular to the first attachment axis (X) and the second attachment axis (Y).

Description

[Technical field]

[0001] The present disclosure relates to a balancer and a robotic system. [Background technology]

[0002] A balancer is known that is disposed between a rotating body of a robot and a first arm that is driven to rotate relative to the rotating body about a horizontal first axis, and that compensates for the gravitational load acting on the first arm (see, for example, Patent Document 1). In a robot equipped with this balancer, a current value of a motor that rotates the first arm relative to the rotating body is monitored to detect a decrease in the force generated by the balancer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-195849 A Summary of the Invention [Problem to be solved by the invention]

[0004] The balancer is attached to the first arm and the rotating body by bearings so as to be rotatable about an axis parallel to the first axis. The force generated by the balancer is transmitted to the first arm and the rotating body via the bearings to generate an auxiliary torque for compensating for the gravity load.

[0005] As the operating time of the robot increases, damage and wear progresses to the bearings that support the force generated by the balancer, which could damage the balancer's mounting parts, the rotating body, or the first arm, so damage and wear to the bearings must be detected early.However, even if the bearings are damaged or worn, the motor current value does not fluctuate significantly, and it is not possible to detect a bearing abnormality based on the motor current value. Therefore, early detection of bearing damage or wear is desirable. [Means for solving the problem]

[0006] One aspect of the present disclosure is a balancer comprising: a housing rotatably attached to one of a first member or a second member by a first bearing so as to be rotatable about a first mounting axis parallel to the rotation axis of a robot having a first member and a second member driven to rotate about a rotation axis relative to the first member; a rod having one end rotatably attached to the other of the first member or the second member by a second bearing so as to be rotatable about a second mounting axis parallel to the rotation axis; force generating means for generating a force in a direction to pull the rod into the housing or in a direction to push the rod out of the housing; and a sensor for detecting at least one of a positional relationship between the first mounting axis and the housing and a positional relationship between the second mounting axis and the rod in a direction perpendicular to the first mounting axis and the second mounting axis. [Brief description of the drawings]

[0007] [Figure 1] 1 is an overall configuration diagram showing a robot system according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing a balancer according to an embodiment of the present disclosure. [Diagram 3] 3 is a partial vertical cross-sectional view illustrating a direction in which a housing of the balancer in FIG. 2 moves due to wear of a bearing that rotatably supports the housing and a first shaft. FIG. [Figure 4] 3 is a partial vertical cross-sectional view illustrating a movement direction of the rod due to wear of a bearing that rotatably supports the rod and a second shaft of the balancer in FIG. 2. FIG. [Diagram 5] 3 is a vertical cross-sectional view for explaining the difference between a distance detected by a sensor in the balancer of FIG. 2 and a distance in a normal state. FIG. [Figure 6] FIG. 3 is a vertical sectional view showing a modified example of the balancer in FIG. 2. [Figure 7] 3 is a vertical cross-sectional view showing a modified example of the arrangement of sensors in the balancer of FIG. 2. FIG. [Figure 8] 3 is a vertical sectional view showing a modified example of the sensor in the balancer of FIG. 2. [Figure 9] 3 is a vertical sectional view showing another modified example of the sensor in the balancer of FIG. 2. FIG. [Figure 10] 3 is a vertical cross-sectional view showing a modified example of the arrangement of sensors in the balancer of FIG. 2. FIG. [Figure 11] 3 is a partial vertical cross-sectional view showing an example of the arrangement of a sensor for detecting the distance between a housing and a first mounting axis, instead of the sensor in the balancer of FIG. 2. FIG. [Figure 12] 3 is a partial vertical cross-sectional view showing an example of the arrangement of a sensor that detects the distance between a rod and a second mounting axis, instead of the sensor in the balancer of FIG. 2. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A balancer 1 and a robot system 100 according to an embodiment of the present disclosure will be described below with reference to the drawings. As shown in FIG. 1, a robot system 100 according to this embodiment includes a robot 110 and a control device 120 that controls the robot 110.

[0009] The robot 110 is, for example, a vertical six-axis articulated robot. The robot 110 includes a base 111 placed on a floor surface F, a rotating body (first member) 112 rotatable relative to the base 111 about a first axis A extending vertically, a first arm (second member) 113 rotatable relative to the rotating body 112 about a horizontal second axis (rotation axis) B, and a balancer 1.

[0010] As shown in FIG. 2, the balancer 1 includes a housing 2, a rod 3, a movable plate (movable member) 4, a compression coil spring (force generating means) 5, and a sensor 6. The housing 2 comprises a cylindrical main body 7, flat front and rear end plates (end plates) 8 and 9 which close both axial ends of the main body 7, and a bearing 12 arranged on the front end plate 8 and supporting the rod 3 so that it can move longitudinally.

[0011] A pair of mounting parts 10 are provided on the outer circumferential surface of the main body 7 at axially opposite positions on either side of the axis. Each mounting part 10 is formed in a cylindrical shape extending in opposite directions on the same straight line radially outward from the outer circumferential surface of the main body 7, and has an inner hole 11 with a circular cross section.

[0012] A through hole 13 is provided in the center of the front end plate 8, penetrating in the plate thickness direction, and a bearing 12 is disposed in this through hole 13. The rod 3 is inserted and supported by the bearing 12 so as to be movable in the axial direction of the main body 7. A mounting bracket 14 is fixed to one end of the rod 3 disposed outside the housing 2. The mounting bracket 14 is provided with a through hole 15 that penetrates in a direction perpendicular to the longitudinal axis C of the rod 3.

[0013] A movable plate 4 is fixed to the other end of the rod 3 disposed inside the housing 2 by fastening a male thread 3a formed on the rod 3 to a nut 16. The movable plate 4 is formed in a disk shape with an outer diameter slightly smaller than the inner diameter of the main body 7.

[0014] In this embodiment, the compression coil spring 5 is disposed in a compressed state between the front end plate 8 through which the rod 3 passes and the movable plate 4. As a result, the rod 3 is constantly subjected to the force generated by the compression coil spring 5 in a direction in which the rod 3 is drawn into the housing 2. Furthermore, when the rod 3 is moved in a direction in which it is drawn out of the housing 2, the amount of compression of the compression coil spring 5 increases, and the force drawing the rod 3 into the housing 2 increases.

[0015] The sensor 6 is, for example, a non-contact distance sensor such as a laser displacement meter, which is fixed to the outside of the rear end plate 9 of the housing 2, irradiates laser light through a through hole 17 provided in the rear end plate 9 toward the end of the rod 3, and detects the reflected light at the end of the rod 3. In the figure, reference numeral 18 denotes a bracket for attaching the sensor 6 to the rear end plate 9 of the housing 2.

[0016] This makes it possible to measure the distance from the tip of the sensor 6 to the end of the rod 3. Measuring the distance from the tip of the sensor 6 fixed to the housing 2 to the end of the rod 3 means detecting the positional relationship between the rod 3 and the housing 2.

[0017] The balancer 1 configured in this manner is attached between the rotating body 112 and the first arm 113 by a pair of a first shaft 19 fixed to the rotating body 112 and a second shaft 20 fixed to the first arm 113. The first shaft 19 and the second shaft 20 are each arranged parallel to the second axis B and spaced apart from each other.

[0018] The first shaft 19 fixed to the rotating body 112 is inserted into the inner hole 11 of the mounting portion 10 provided in the housing 2 of the balancer 1, and supports the housing 2 rotatably around the first mounting axis X by a bearing, such as a sliding bearing (first bearing) 21, arranged between the outer surface of the first shaft 19 and the inner surface of the inner hole 11. The second shaft 20 fixed to the first arm 113 is inserted into a through hole 15 provided in the mounting bracket 14 of the rod 3, and supports the rod 3 rotatably around the second mounting axis Y by a bearing, such as a rolling bearing (second bearing) 22, arranged between the outer surface of the second shaft 20 and the inner surface of the through hole 15.

[0019] As a result, when the first arm 113 is rotated about the second axis B with respect to the rotating body 112, the second shaft 20 fixed to the first arm 113 moves about the second axis B, and as a result, the distance between the first mounting axis X and the second mounting axis Y changes, and the compression amount of the compression coil spring 5 inside the housing 2 changes. In the state of FIG. 1 in which the first arm 113 is arranged in the vertical direction, the gravity load torque acting on the first arm 113 is the smallest, and as the first arm 113 tilts forward or backward and the inclination angle with respect to the vertical direction increases, the gravity load torque acting on the first arm 113 increases.

[0020] On the other hand, in the balancer 1, the compression amount of the compression coil spring 5 is larger when the first arm 113 is inclined forward or backward with respect to the vertical direction than when the first arm 113 is disposed in the vertical direction. Moreover, the distance between the second axis B and the plane including the first mounting axis X and the second mounting axis Y is larger when the first arm 113 is inclined forward or backward with respect to the vertical direction than when the first arm 113 is disposed in the vertical direction.

[0021] As a result, the auxiliary torque generated by the balancer 1 can be changed in a pattern that is large when the gravity load torque acting on the first arm 113 is large and is small when the gravity load torque acting on the first arm 113 is small, thereby reducing the load on the motor over the entire operating range of the first arm 113.

[0022] The control device 120 includes at least one processor, at least one memory, and a display (notification unit) 121. Under normal conditions, the control device 120 stores the distance detected by the sensor 6 when the first arm 113 is at a predetermined angle, for example, 0°, relative to the rotating body 112, i.e., when the first arm 113 is positioned vertically as shown in FIG. 1.

[0023] Here, the normal state refers to a time when the sliding bearing 21 and the rolling bearing 22 supporting the balancer 1 are not deteriorated, such as when the robot 110 is shipped or immediately after the first and second bearings 21, 22 supporting the balancer 1 are replaced. The distance to be stored may be a distance actually detected by the sensor 6, or a design value may be stored.

[0024] Furthermore, the processor of the control device 120 manually or periodically as necessary, or while the first arm 113 is positioned vertically while the robot 110 is in operation, calculates the difference between the distance detected by the sensor 6 and the normal distance stored in the memory. The processor of the control device 120 then determines whether or not the absolute value Δ of the calculated difference exceeds a predetermined threshold, and when it determines that the absolute value Δ of the difference exceeds the threshold, notifies the display 121 that an abnormal state has occurred in the balancer 1.

[0025] The operation of the balancer 1 and the robot system 100 according to this embodiment configured as described above will be described below. According to the balancer 1 of this embodiment, the elastic force of the compression coil spring 5 acts in a direction that always draws the rod 3 into the housing 2. Therefore, in order to support the housing 2 pulled forward by the compression coil spring 5, the slide bearing 21 provided on the first shaft 19 side receives a load due to the elastic force of the compression coil spring 5 only on the rear side of the first shaft 19. Also, in order to support the rod 3 pulled backward by the compression coil spring 5, the rolling bearing 22 provided on the second shaft 20 side receives a load due to the elastic force of the compression coil spring 5 only on the front side of the second shaft 20.

[0026] Then, when the robot 110 operates for a long time with the uneven load constantly acting as described above, if the sliding bearing 21 wears out, the housing 2 moves forward relative to the first shaft 19, as shown by the arrow P in Fig. 3. If the rolling bearing 22 wears out, the rod 3 moves backward relative to the second shaft 20, as shown by the arrow Q in Fig. 4. It is assumed that wear has occurred in the bearings 21, 22 in the hatched portions in Figs. 3 and 4.

[0027] As a result, in either case where the sliding bearing 21 is worn or where the rolling bearing 22 is worn, the distance detected by the sensor 6 becomes smaller than the stored normal distance, as shown by the dotted line in Figure 5. According to the robot system 100 of this embodiment, when the absolute value Δ of the difference between the distance detected by the sensor 6 and the normal distance exceeds a predetermined threshold, an abnormal state is notified on the display 121. This has the advantage that measures such as replacing the bearings 21, 22 can be taken before the wear of the sliding bearing 21 and the rolling bearing 22 supporting the balancer 1 progresses further and adversely affects other parts.

[0028] That is, although it is difficult to detect early wear of the bearings 21, 22 from the motor current value, it is possible to detect and deal with an abnormal state by detecting the positional relationship between the rod 3 and the housing 2, which changes due to wear. In particular, when the bearings 21, 22 that respectively support the rod 3 and the housing 2 wear simultaneously, the abnormal state can be detected at an earlier stage by the total value of the wear amounts of both the bearings 21, 22.

[0029] In this embodiment, the balancer 1 is exemplified as one in which the compression coil spring 5 generates a force in a direction that draws the rod 3 into the housing 2. Alternatively, as shown in Fig. 6, the compression coil spring 5 may be disposed between the movable plate 4 and the rear end plate 9, and the balancer 1 may generate a force in a direction that pushes the rod 3 out of the housing 2 by the compression coil spring 5.

[0030] In this case, a through hole 23 may be provided in the front end plate 8, and the distance to the movable plate 4 may be detected by a sensor 6, such as a laser displacement meter, fixed to the front end plate 8. Then, the distance or the design value detected by the sensor 6 under normal conditions may be stored, and it may be determined as necessary or periodically whether the absolute value Δ of the difference between the distance detected by the sensor and the distance under normal conditions exceeds a threshold value.

[0031] In this embodiment, a laser displacement meter fixed to the rear end plate 9 is used as the sensor 6, and detects the reflected light of the laser light at the end face of the rod 3. Alternatively, as shown in Fig. 7, the distance to the movable plate 4 (or the nut 16) fixed to the rod 3 may be detected.

[0032] In this embodiment, the normal distance is stored and it is determined whether the absolute value Δ of the difference between the normal distance and the detected distance exceeds a threshold value. This makes it possible to arbitrarily set the angle of first arm 113 with respect to rotating body 112 when detecting the distance.

[0033] Alternatively, when detecting the distance at the stroke end of the rod 3, a distance obtained by subtracting the threshold from the normal distance may be stored as a new threshold, and it may be determined whether the detected distance is equal to or less than the new threshold. The distance corresponding to the new threshold is usually outside the stroke end, and is a distance that cannot be reached in the normal operating state of the robot 110. This makes it possible to detect an abnormal state when the detected distance is equal to or less than the threshold, without setting the angle of the first arm 113 relative to the rotating body 112 when detecting the distance.

[0034] As a sensor, instead of a distance sensor 6 such as a laser displacement meter, a contact switch such as a limit switch (switch) 24 or a non-contact switch such as a proximity sensor may be used as shown in Fig. 8. Even in this case, by arranging the limit switch 24 at a position where it operates when the rod 3 reaches a position beyond the stroke end, it is possible to detect an abnormal state at the time when the limit switch 24 operates.

[0035] 9, an optical sensor may be used in place of the distance sensor 6 such as a laser displacement meter, in which a light emitter 25 and a light receiver 26 are arranged opposite to each other on the main body 7 of the housing 2, and the optical axis L of the light emitted from the light emitter 25 is arranged at a position beyond the stroke end of the rod 3. When the positional relationship between the housing 2 and the rod 3 changes due to wear of the bearings 21, 22, the rod 3 (or the movable plate 4 or the nut 16) blocks the optical axis L, and it can be detected that the absolute value Δ of the difference exceeds a threshold value.

[0036] Also, instead of using the sensor 6 to detect the distance between the rear end plate 9 and the rod 3, the sensor 6 may detect the distance between the front end plate 8 and the mounting bracket 14 as shown in Fig. 10. Since there is no need to place the sensor 6 inside the housing 2, this can be applied to cases where the balancer 1 is a spring balancer having a built-in compression coil spring 5, as well as a gas balancer filled with gas.

[0037] Furthermore, in this embodiment, the positional relationship between the housing 2 and the rod 3 is detected by the sensor 6, and whether or not an abnormal state exists is determined based on the total displacement of the housing 2 relative to the first shaft 19 and the displacement of the rod 3 relative to the second shaft 20. Alternatively, as shown in Fig. 11, the sensor 6 may detect the distance between the first mounting axis X in the axial direction of the housing 2 (direction perpendicular to both the first mounting axis X and the second mounting axis Y) and the outer surface of the mounting portion 10 (housing 2). Also, as shown in Fig. 12, the sensor 6 may detect the distance between the second mounting axis Y in the axial direction of the rod 3 (direction perpendicular to both the first mounting axis X and the second mounting axis Y) and the end face of the mounting bracket 14 (rod 3). Also, the distances in Figs. 11 and 12 may be detected separately.

[0038] Since the degree of wear of the bearings 21, 22 differs depending on the types of bearings 21, 22 they support or the differences in the loads on each bearing 21, 22, it is possible to detect each bearing 21, 22 separately and determine whether or not an abnormal state exists using different threshold values. For example, the amount of wear of the rolling bearing 22 is likely to be greater than that of the plain bearing 21, and in the example of Fig. 1, the amount of wear of the two plain bearings 21 is sufficiently smaller than that of a single rolling bearing 22. Therefore, by detecting the variation in distance for each bearing 21, 22 and determining whether or not an abnormal state exists using different threshold values, wear of the bearings 21, 22 can be found individually and measures can be taken at an early stage.

[0039] In addition, in this embodiment, a vertical six-axis articulated robot is exemplified, but the type of robot 110 may be arbitrary. In addition, the housing 2 is rotatably supported on the rotating body 112, and the rod 3 is rotatably supported on the first arm 113, but the reverse may be true. In addition, the support position of the housing 2 on the rotating body 112 is set to a midpoint in the axial direction of the housing 2, but the present invention may be applied to a balancer 1 that is supported behind the rear end plate 9. [Explanation of symbols]

[0040] 1. Balancer 2. Housing 3. Rod 4 Movable plate (movable part) 5 Compression coil spring (force generating means) 6 Distance Sensors 7 Main body 8 Front end plate (end plate) 9 Rear end plate (end plate) 21 Plain bearing (first bearing) 22 Rolling bearing (second bearing) 24 Limit switch (switch, sensor) 25 Light emitter (sensor) 26 Receiver (sensor) 100 Robot System 110 Robot 112 Rotating body (first member) 113 First arm (second member) 121 Display (notification unit) B Second axis (rotation axis) X First mounting axis Y Second mounting axis

Claims

1. a housing attached to one of a first member or a second member of a robot, the second member being rotationally driven about a rotation axis relative to the first member, by a first bearing so as to be rotatable about a first attachment axis parallel to the rotation axis; a rod having one end attached to the other of the first member or the second member by a second bearing so as to be rotatable about a second attachment axis parallel to the rotation axis; a force generating means for generating a force in a direction to draw the rod into the housing or in a direction to push the rod out of the housing; a sensor that detects at least one of a positional relationship between the first mounting axis and the housing and a positional relationship between the second mounting axis and the rod in a direction perpendicular to the first mounting axis and the second mounting axis.

2. the housing includes a cylindrical main body and an end plate that closes one axial end of the main body, a movable member fixed to the other end of the rod disposed within the body portion; 2. The balancer according to claim 1, wherein said force generating means is a compression coil spring disposed between said end plate and said movable member.

3. 3. The balancer according to claim 1, wherein the sensor is a distance sensor that detects a distance.

4. 3. The balancer according to claim 1, wherein the sensor is a switch that detects when the positional relationship reaches a predetermined state.

5. A robot comprising the balancer according to any one of claims 1 to 4; and an alarm unit that notifies the occurrence of an abnormal condition when a difference between the positional relationship detected by the sensor and the positional relationship under normal conditions exceeds a predetermined threshold value when the first member and the second member are disposed in a specific relative position.

6. a housing attached to one of a first member or a second member of a robot, the second member being rotationally driven about a rotation axis relative to the first member, by a first bearing so as to be rotatable about a first attachment axis parallel to the rotation axis; a rod having one end attached to the other of the first member or the second member by a second bearing so as to be rotatable about a second attachment axis parallel to the rotation axis; a force generating means for generating a force in a direction to draw the rod into the housing or in a direction to push the rod out of the housing; a balancer including a sensor that detects a positional relationship between the housing and the rod in a direction perpendicular to the first mounting axis and the second mounting axis; and means for detecting damage and wear of the first bearing and the second bearing based on the positional relationship.

7. The housing comprises a cylindrical main body and an end plate closing one axial end of the main body, a movable member fixed to the other end of the rod disposed within the body portion; 7. The robot system according to claim 6, wherein the force generating means is a compression coil spring disposed between the end plate and the movable member.

8. A robot system as described in claim 6 or claim 7, wherein the sensor is a distance sensor that detects distance.

9. A robot system as described in claim 6 or claim 7, wherein the sensor is a switch that detects when the positional relationship reaches a predetermined state.

Images