ROBOT

A robot includes a plurality of joints including a first joint and a second joint, wherein each of the first joint and the second joint including a first support member, a second support member facing the first support member and configured to be displaceable relative to the first support member, an elastic member configured to connect the first support member and the second support member, and a torque sensor including a detection unit configured to detect a relative displacement amount between the first support member and the second support member, and wherein a number of the elastic members of the torque sensor in the first joint is different from a number of the elastic members of the torque sensor in the second joint.

BACKGROUND

Field of the Disclosure

The present disclosure relates to a robot.

Description of the Related Art

Robot apparatuses are used in production lines of various industrial products. These types of robot apparatuses are required to meet demands that operations should be performed highly accurately to assemble work, such as soft objects, light objects, and low-strength members.

Japanese Patent Application Laid-open No. H10-286789 discusses a configuration in which a torque detection device for detecting torque applied to a joint is disposed in each joint of a robot arm, as a method of detecting forces acting on a piece of work.

According to the configuration discussed in Japanese Patent Application Laid-open No. H10-286789, a same sensor is disposed in all joints. However, in a case of a multi-joint robot, operation environments of individual joints are different from each other in accordance with the ambient environment of a motor, a speed reducer, and the like. Consequently, if the same sensor is disposed in all the joints, the operation accuracy of the multi-joint robot may be decreased.

SUMMARY

Aspects of the present disclosure are directed to a technique for improving an operation accuracy of a robot.

According to an aspect of the present disclosure, a robot includes a plurality of joints including a first joint and a second joint, wherein each of the first joint and the second joint including a first support member, a second support member facing the first support member and configured to be displaceable relative to the first support member, an elastic member configured to connect the first support member and the second support member, and a torque sensor including a detection unit configured to detect a relative displacement amount between the first support member and the second support member, and wherein a number of the elastic members of the torque sensor in the first joint is different from a number of the elastic members of the torque sensor in the second joint.

DESCRIPTION OF THE EMBODIMENTS

Hereinbelow, embodiments of the present disclosure will be described with reference to the attached drawings. Note that each of the embodiments described below is merely one embodiment, and the present disclosure is not limited thereto. In addition, common configurations are described with reference to a plurality of drawings mutually, and redundant descriptions of components with the same symbols or numbers are omitted as appropriate. Different items with a same name can be distinguished by adding “first” or “second” at the head of each item, like “first item” or “second item”.

With reference toFIGS.1A and1B, an example configuration of a torque sensor600(hereinbelow, simply referred to as a sensor600) for detecting a torque according to a first embodiment.

The sensor600is provided in each of joints J1to J6. The sensor600includes detection units604for detecting torque applied to the sensor600and a structure614. The structure614can be a structure including a support member601, a support member602facing the support member601, elastic members603connecting the support members601and602. The structure614can be integrally formed as a unit or can be formed by combining separate members. The sensor600is not necessarily provided in each of all the joints J1to J6and can be provided in each of two or more joints among the joints J1to J6.

Each portion of the structure614is formed of a predetermined material, such as resin and metal (e.g., steel or stainless-steel), with an elastic (spring) coefficient satisfying a target torque detection range and a required resolution. A plurality of the elastic members603(twelve, in this example) is arranged around a rotation axis613. The sensor600with a desired elastic (spring) coefficient is formed by selecting the number of the elastic members603, a shape (thickness), and a material. The structure614can be produced using a three-dimensional (3D) printer. More specifically, the structure614can be produced by generating slice data, which is data for the 3D printer, from design data (e.g., computer-aided design (CAD) data) of the structure614and inputting the slice data into a conventional 3D printer.

Four detection units604are arranged at approximately 90 degree intervals. While, in the present embodiment, the number of the detection units604is four, but one or a plurality of the detection units604can be disposed as long as at least one detection unit604is provided.

FIG.1Bis a cross-section diagram illustrating the detection unit604disposed in the sensor600. A detection substrate610provided with a detection head611is bonded and fixed to a stay609(double-sided adhesive tape can also be used) for fixing the detection substrate610. The stay609is bonded and fixed to the support member601. A scale612reflecting light emitted from the detection head611is bonded and fixed to the support member602.

The detection substrate610has a function of an optical position sensor (encoder). The detection head611is configured of a reflection type optical sensor including a light-emitting element (not illustrated) and a light-receiving element (not illustrated). The scale612has a pattern surface facing the detection head611, and the pattern surface has a scale pattern (not illustrated in detail). The scale pattern has shades and reflection ratios in regular arrangements formed by using a predetermined pattern.

The detection head611emits light from the light-emitting element to the scale612, and the light-receiving element receives the light reflected by the scale612. In this configuration, in a case where torque around the rotation axis613acts on the sensor600and the structure614deforms in an x-axis direction, a relative position between the detection head611and the scale612changes, and consequently a position of the light emitted onto the scale612moves on the scale612. In this state, in a case where the light emitted onto the scale612passes through the scale pattern on the scale612, the light amount detected by the light-receiving element of the detection head611changes. Based on the change of the light amount, a relative displacement amount between the scale612and the detection head611is detected.

The displacement amount detected by the detection head611is converted into a torque acted on the structure614by a torque-detection control unit implemented by a control routine executed by a control apparatus300.

In the present embodiment, as illustrated inFIG.1A, the two detection units604are arranged at opposing positions on a same diameter with the rotation axis613as a reference. In this case, calculation processing of an average value obtained by averaging torque detection values output from the corresponding detection heads611is performed. In this way, influences of other axial forces acting on directions other than the target torque detection direction can be reduced.

Further, a detection value related to the relative displacement is obtained from the detection units604arranged on line symmetry positions or point symmetry positions on a same diameter with the rotation axis613as a center. Accordingly, by averaging outputs of the plurality of detection units604, highly accurate and highly reliable relative displacement information or the torque detection value based on the relative displacement information can be obtained. As described above, since the torque detection value is obtained by the averaging, accuracy of the torque detection value increases with an increase in the number of the detection units604. On the other hand, the increase of the number of the detection units604increases the cost. Thus, the number of the detection units604suitable for the torque of each of the joints J1to J6needs to be determined efficiently.

Next, with reference toFIG.2, a robot apparatus100including the above-described sensors600will be described.

The robot apparatus100includes a robot arm (robot)200as a multi-joint robot, the control apparatus300for controlling the robot arm200, and a teaching pendant400. The teaching pendant400is a teaching device that transmits data of a plurality of teaching points to the control apparatus300and is used by an operator to designate an operation of the robot arm200.

While, in the present embodiment, the robot arm200is a 6-joint robot, the number of joints can be any number more than one. The robot arm200includes a plurality of servomotors201to206for rotationally driving the joints J1to J6around joint axes A1to A6, respectively. The robot arm200can move a leading end of the robot arm200to take any attitude at any three-dimensional position in three directions within a movable range. In general, the position and the attitude of the robot arm200can be expressed using a coordinate system. “To” indicates a coordinate system fixed to a base250of the robot arm200, and “Te” indicates a coordinate system fixed to a hand leading end portion of the robot arm200.

In the present embodiment, the servomotors201to206include electric motors211to216, respectively, and sensor units221to226, respectively, and the sensor units221to226are connected to the electric motors211to216, respectively. The sensor units221to226each include an angle sensor and the sensor600. The angle sensor detects a corresponding angle of the joints J1to J6, and the sensor600detects corresponding torque of the joints J1to J6. The servomotors201to206are connected to respective driving frames in the joints J1to J6.

The robot arm200further includes a servo control unit230serving as a drive control unit for controlling the electric motors211to216of the servomotors201to206. Based on input torque command values, the servo control unit230outputs current commands to the electric motors211to216to adjust torques of the joints J1to J6to be at the torque command values, whereby operations of the electric motors211to216are controlled. While, in the present embodiment, the servo control unit230configured of one control unit is described, the servo control unit230suitable for each of the electric motors211to216can be provided.

For example, a hand for grasping a work can be attached to the leading end of the robot arm200. Using the attached hand, the robot apparatus100can perform a job for manufacturing articles, for example, grasping a work and assembling the grasped work to a different work. In addition, a screwdriver can be attached to the leading end of the robot arm200so that the robot apparatus100can tighten screws. Accordingly, the robot apparatus100can primarily perform a job to process the work by using the leading end of the robot arm200. In the present embodiment, the process also includes a job of grasping and moving a work. Further, the robot arm200can work, even though a worker is present near the robot, in cooperation with the worker.

Next, a configuration of the control apparatus300will be schematically described with reference toFIG.3. The control apparatus300includes a calculation device301serving as a control unit. The calculation device301is configured of a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), or a Field-Programmable Gate Array (FPGA). The control apparatus300includes a Read Only Memory (ROM)302and a main storage device303, such as a Random Access Memory (RAM). The ROM302stores a program330, such as a Basic Input/Output System (BIOS), for operating the calculation device301. The main storage device303is a storage device for temporarily storing various kinds of data, such as a calculation processing result of the calculation device301. The control apparatus300includes an auxiliary storage device304serving as a storage unit, such as a Hard Disk Drive (HDD) and a Solid State Drive (SSD). The auxiliary storage device304stores a calculation processing result of the calculation device301, or data obtained from outside. In addition, the control apparatus300includes a recording disk drive305and various kinds of interfaces306to309.

The ROM302, the main storage device303, the auxiliary storage device304, the recording disk drive305, and the various kinds of interfaces306to309are connected to the calculation device301via a bus310.

The teaching pendant400is connected to the interface306, and the calculation device301receives an input of data of teaching points from the teaching pendant400via the interface306and the bus310.

A monitor321is connected to the interface307to display various kinds of images thereon.

An external storage device322is connected to the interface308, and can be a rewritable non-volatile memory or an external HDD.

The servo control unit230is connected to the interface309, and the calculation device301outputs data of a target torque for each of the joints J1to J6to the servo control unit230at a predetermined time interval via the bus310and the interface309.

The recording disk drive305can read out various kinds of data, programs, or the like recorded in a recording disk (recording medium)331. A recording medium for recording the programs according to the present embodiment is not limited to the recording disk331, and examples of the recording medium include a non-volatile memory and an external HDD.

FIG.4is an enlarged view of each of the joints J1to J6including the sensor600.

The sensor600is connected to a speed reducer1101via a sensor attachment member1103, and the speed reducer1101is connected the servomotors201to206.

The structure614of the sensor600is elliptically deformed by the influence of a rotational vibration due to the servomotors201to206and the speed reducer1101connected to the servomotors201to206. When the structure614is elliptically deformed, the stay609is deformed, and consequently, the detection head611is displaced. As a result, the torque is erroneously detected. Such an influence increases with an increase in transmission efficiency of the deformation of the speed reducer1101to the sensor600.

In other words, the erroneous detection of torque easily occur with the speed reducer1101or the sensor attachment member1103having lower stiffness. Accordingly, in a case of using the speed reducer1101having low stiffness or the sensor attachment member1103having low stiffness, the number of the detection units604of the sensor600is increased, whereby erroneous detection of torque can be reduced in a case where the elliptical deformation occurs. In this way, a highly accurate torque detection can be performed in each of the joints J1to J6.

In this configuration, the servomotors201to206or the speed reducers1101each suitable for the corresponding joint of the joints J1to J6are used. For example, the servomotors201to206or the speed reducers1101having rated outputs different from each other are used among the joints J1to J6. Since the control apparatus300performs force control or position control based on the servomotors201to206of the joints J1to J6, the sensor600desirably covers the rated range of each of the servomotors201to206. On the other hand, if the rated range of each sensor600is set too large more than necessary, a required resolution may not be obtained. Thus, the operation accuracy of the robot arm200can be improved by making the stiffness of the sensor600mounted on each of the joints J1to J6suitable for the corresponding joint.

The distance between the speed reducer1101and the sensor600is a factor in increasing transmission efficiency of the deformation of the speed reducer1101to the sensor600. The distances between the speed reducer1101and the sensor600in the joints J1to J6are different from each other depending on the design of the robot arm200, and if the distance is short, the influence due to the deformation of the speed reducer1101on the sensor600becomes large.

In view of the foregoing, in the present embodiment, the number of the detection units604is adjusted based on the stiffness of the speed reducer1101, the stiffness of the torque sensor attachment member1103, and the difference in the distance between the speed reducer1101and the sensor600.

A robot arm with an operation accuracy improved can be provided by mounting the sensor600suitable for each of the joints J1to J6thereon.

For example, in a case where the distance between the speed reducer1101and the sensor600is short, the operation accuracy of the robot arm200can be maintained by increasing the number of the detection units604.

The sensor600mounted on each of the joints J1to J6of the robot arm200is required to have a high torque detection accuracy in addition to the above-described stiffness. With an increase in the number of the detection units604, the higher accuracy can be obtained by the averaging effect. However, by taking the balance of the cost and size in consideration, it is desirable to determine the number of the detection units604suitable for each of the joints J1to J6.

For example, in the torque sensor that is for a joint less affected by forces in other axial directions, disposing one detection unit604is sufficient, and in the torque sensor that is for a joint largely affected by the deformation of the speed reducer, disposing four or more of the detection units604is desirable.

Next, with reference toFIG.5, a description is given of the sensor600having a configuration different from the sensor600illustrated inFIG.1A, among the sensors600according to the present embodiment.

The sensor600inFIG.5is different from the sensor600inFIG.1Ain that the number of the detection units604is changed from four to two, and the number of the elastic members603is changed from twelve to eight.

In the present embodiment, the sensor600is improved in resolution, by reducing the number of the elastic members603to reduce the stiffness of the sensor600. In this way, it is possible to provide the sensor600having a stiffness suitable for each of the joints J1to J6, and thus the operation accuracy of the robot arm200can be improved. Further, the thickness and the material of the elastic members603are standardized to use the elastic members603as a common component for the joints J1to J6, so that the sensor600having a stiffness suitable for each of the joints J1to J6can be easily provided. The stiffness of the sensor600can also be reduced by reducing the size of the sensor600.

As described above, the number of the elastic members603of each of the sensors600is increased with magnitude of the rated output of each of the servomotors201to206and the rated output of each of the speed reducers1101in the joints J1to J6. Further, in a case of using the servomotors201to206having a small rated output or the speed reducers1101having a small rated output in the joints J1to J6, the number of the elastic members603of each of the sensors600is reduced. In this way, the design time spent for the sensor600can be reduced, and the sensor600suitable for each of the joints J1to J6can be provided.

The size of the servomotors201to206mounted on the joints J1to J6of the robot arm200decreases in order of decreasing distance to the leading end of the robot arm200. Along with the size reduction of the servomotors201to206, the stiffness required for the sensor600becomes smaller. Thus, it is desirable to reduce the number of the elastic members603of the sensor600in accordance with the position of the sensor600in order of decreasing distance to the leading end of the robot arm200. More specifically, the joint on a side close to the base250desirably includes more elastic members603in the sensor600than the joint on a side close to the leading end of the robot arm200.

For example, as illustrated inFIG.6, the sensor600including twelve elastic members603is mounted on the joint J1of the robot arm200, and the sensor600including eight to twelve elastic members603is mounted on each of the joints J2and J3. For example, the sensor600including four to eight elastic members603is mounted on each of the joints J4and J5, and the sensor600including four elastic members603is mounted on the joint J6. The difference between the numbers of the elastic members603among the joints J1to J6is eight or less.

Alternatively, the sensor600including eight detection units604is mounted on the joint J1of the robot arm200, and the sensor600including four to eight elastic members603is mounted on each of the joints J2and J3. For example, the sensor600including two to four elastic members603is mounted on each of the joints J4and J5, and the sensor600including one elastic member603is mounted on the joint J6. The difference between the numbers of the elastic members603among the joints J1to J6is seven or less.

Adjusting the resolution and the accuracy of the joint J6of the robot arm200to be higher than the resolution and the accuracy of the other joints, i.e., the joint J1to J5, leads to highly accurate operation of the robot arm200on the work.

For example, a first joint described in claims is not limited to the joint J1, and can be any joint among the joints J1to J6. Similarly, an N-th joint described in claims can be any joint among the joints J1to J6.

Next, with reference toFIG.7, a configuration of each of the joints J1to J6of the robot arm200according to a second embodiment will be described. The present embodiment is different from the first embodiment in that the number of the elastic members603and the number of the detection units604are different from each other among the joints J1to J6.

In the present embodiment, the stiffness of the sensor600is increased by increasing the number of the elastic members603in the joint J6of the robot arm200. Accordingly, the robot arm200can be appropriately applied to even such a job that does not require high resolution and high accuracy to the joint J6, whereby the increase of cost can be suppressed or reduced.

Next, with reference toFIG.8, a configuration of each of the joints J1to J6of the robot arm200according to a third embodiment will be described. The present embodiment is different from the first and second embodiments in that the number of the elastic members603and the number of the detection units604are different from each other among the joints J1to J6.

More specifically, the number of the elastic members603and the number of the detection units604are alternately set among the joints J2to J5. Like the present embodiment, the stiffness of the joint desired to increase the resolution and accuracy can be reduced.

Next, with reference toFIG.9, a configuration of each of the joints J1to J6of the robot arm200according to a fourth embodiment will be described. In the present embodiment, the number of the elastic members603and the number of the detection units604are different from each other among the joints J1to J6in a manner different from the first to third embodiments.

More specifically, in the present embodiment, the number of the elastic members603and the number of the detection units604are increased in the order of the joints J1to J6. Accordingly, the present embodiment is applicable to the robot arm200that is required to have the joint J1having the highest resolution and accuracy among the joints J1to J6.

Not limited to the first to fourth embodiments, the number of the elastic members603and the number of the detection units604in each of the joints J1to J6can be set arbitrarily based on the desired performance.

Next, with reference toFIG.10, a description will be given of a case where the number of joints of the robot arm200according to a fifth embodiment is three (i.e., joint A, joint B, and joint C). The joint A is a joint disposed on the side close to the base250, and the joint C is a joint disposed on the side close to the leading end of the robot arm200.

In the present embodiment, the stiffness of the joints A to C are different from each other. For example, in a case of a table at the top inFIG.10, the stiffness is decreased in the order from the joint A, joint B, to joint C. On the other hand, in a case of a table at the bottom inFIG.10, the stiffness is increased in the order from the joint A, joint B, to joint C.

As shown in other tables, the stiffness of the joint A, joint B, and joint C can be arranged arbitrarily.

In the present embodiment, the case where the number of joints is three (i.e., joints A to C) is described, but the number of joints can be two, or four or more.

Next, with reference toFIGS.11to16, the sensor600according to a sixth embodiment will be described.

The sensor600according to the present embodiment is different from the sensor according to the first embodiment in that the sensor600is a distributed torque sensor800(hereinbelow, simply referred to as a distributed sensor800) in which sensor units804each including a detection unit is formed separately, and thus the elastic members603are distributed.

The distributed sensor800includes a plurality of the sensor units804. The plurality of the sensor units804is desirably arranged to face each other.

FIG.12illustrates a configuration of the sensor unit804. Similar to the detection unit604according to the first embodiment, the sensor unit804includes a detection substrate910, a detection head911, and a scale912.

While, in the present embodiment, a stay906supports the scale912, the stay906can also support the detection head911. The sensor unit804includes the support member601, the support member602, and a pair of elastic members903, and the displacement of the elastic members903is detected by the detection head911and the scale912.

When the distributed sensor800is mounted on each of the joints J1to J6of the robot arm200, for example, a link member801and a link member802illustrated inFIG.13can be used.

The link members801and802includes positioning portions1001and1002, respectively, to fit with the sensor unit804.

FIG.14is a top view illustrating the distributed sensor800in which eight sensor units804are disposed. The distributed sensor800suitable for each of the joints J1to J6can be easily disposed, by adjusting the number of the sensor units804in the distributed sensor800based on the desired stiffness and the resolution. While the sensor units804each have a shape with a concave portion at the center, not all the sensor units804need to have a same shape. Alternatively, the sensor units804with different shapes among joints J1to J6can be used. A distance from a rotation axis813to each of the sensor units804does not need to be equal, and the distance can be changed in accordance with the passage of each wiring line. With the similar reason, the sensor units804can be shifted from each other to a Z direction, i.e., not need to be arranged on the same plane.

FIG.15illustrates a block elastic body900that is a unit with the detection unit removed from the sensor unit804. The block elastic body900has a configuration unable to detect torque, different from the above-described sensor unit804.

The sensor unit804and the block elastic body900can be fixed to the link members801or802with, for example, screws, and thus can be easily detached and also replaced.

FIG.16is a top view illustrating the distributed sensor800including two block elastic bodies900and six sensor units804. The distributed sensor800includes the block elastic bodies900as non-detection units that do not detect torque. In this way, the stiffness and resolution can be adjusted without changing the number of the positioning portion1001of the link member801and the positioning portion1002of the link member802, in accordance with adjustment of the number of the sensor units804. Accordingly, it is possible to easily arrange the distributed sensor800suitable for each of the joints J1to J6while maintaining the operation accuracy of the robot arm200. For example, it is also possible to reduce the weight of the leading end of the robot arm200by changing the thicknesses or heights of the sensor units804or the elastic members903of the block elastic bodies900in the joint J6.

The embodiments described above can be appropriately modified and changed without departing from the spirit and scope of the technological thought.

For example, a plurality of the embodiments can be combined. Further, a part of the items of at least one embodiment can be eliminated or replaced.

Further, a new item can be added to at least one embodiment. The disclosed contents of the present specification include not only the contents explicitly described in the present specification, but also all the contents understandable from the present specification and/or the drawings attached to the present specification.

Further, the disclosed contents of the present specification include a complementary set of the individual concept described in the present specification. More specifically, if, for example, there is a description of “A is more than B” in the present specification, and even if there is no description of “A is not more than B”, it should be understood that the present specification also discloses that “A is not more than B”. It is because if “A is more than B” is described, the case of “A is not more than B” is taken in consideration, as a premise.

According to the present disclosure, it is possible to provide an advantageous technique for improving the operation accuracy of the robot.

This application claims the benefit of priority from Japanese Patent Application No. 2021-210671, filed Dec. 24, 2021, which is hereby incorporated by reference herein in its entirety.