Robot

A robot includes a base, a robot arm having a first arm coupled to the base and rotating about a first axis, and a force detection unit provided in the base and detecting a force acting on the base or the robot arm, wherein the first arm is coupled to the base in a position shifted from a first center line passing through a center of the base and being parallel to the first axis, and a second center line passing through a center of the force detection unit and being parallel to the first axis is closer to the first axis than the first center line.

The present application is based on, and claims priority from JP Application Serial Number 2019-119690, filed Jun. 27, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a robot.

2. RELATED ART

Recently, in factories, due to labor cost rise and labor shortage, work manually performed in the past has been increasingly automated by various robots and robot peripherals. The various robots include e.g. bases, arms supported by the bases, and force sensors as shown in JP-A-2018-080941. In the robots, the arms are controlled based on detection results of the force sensors.

In the robot disclosed in JP-A-2018-080941, the force sensor is provided below the base. Accordingly, load of the base and the arm is applied onto the force sensor. During actuation of the robot, for example, when an external force is applied to the arm, the force is transmitted to the force sensor via the arm and the base. The force may be detected and the arm may be controlled based on the detection result.

However, when the arm is coupled to a position shifted from a center line of the base, in the configuration as shown in JP-A-2018-080941, i.e., the configuration in which the center axis of the force sensor and the center axis of the base coincide, torque under the arm's weight is constantly applied to the force sensor. The detection accuracy of the force sensor may be lower depending on the magnitude of the torque.

SUMMARY

The present disclosure can be implemented as follows.

A robot according to an application example includes a base, a robot arm having a first arm coupled to the base and rotating about a first axis, and a force detection unit provided in the base and detecting a force acting on the base or the robot arm, wherein the first arm is coupled to the base in a position shifted from a first center line passing through a center of the base and being parallel to the first axis, and a second center line passing through a center of the force detection unit and being parallel to the first axis is closer to the first axis than the first center line.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As below, a robot according to the present disclosure will be explained in detail based on preferred embodiments shown in the accompanying drawings.

First Embodiment

FIG. 1is the side view showing the first embodiment of the robot system including the robot according to the present disclosure.FIG. 2is the block diagram of the robot system shown inFIG. 1.FIG. 3is the side view of the force detection unit shown inFIG. 1.FIG. 4is the sectional view along line A-A inFIG. 3.FIG. 5is the schematic diagram of the robot shown inFIG. 1.

InFIGS. 1 and 3 to 7, for convenience of explanation, an x-axis, a y-axis, and a z-axis are shown as three axes orthogonal to one another. Hereinafter, directions parallel to the x-axis are also referred to as “x-axis directions”, directions parallel to the y-axis are also referred to as “y-axis directions”, and directions parallel to the z-axis are also referred to as “z-axis directions”. Further, hereinafter, the head sides of the respective arrows are referred to as “+(plus)” and tail sides are referred to as “− (minus)”, a direction parallel to the +x-axis direction is also referred to as “+x-axis direction”, a direction parallel to the −x-axis direction is also referred to as “−x-axis direction”, a direction parallel to the +y-axis direction is also referred to as “+y-axis direction”, a direction parallel to the −y-axis direction is also referred to as “−y-axis direction”, a direction parallel to the +z-axis direction is also referred to as “+z-axis direction”, and a direction parallel to the −z-axis direction is also referred to as “−z-axis direction”. Furthermore, a direction about the z-axis and a direction about an axis parallel to the z-axis are also referred to as “u-axis directions”.

Hereinafter, for convenience of explanation, the +z-axis direction inFIG. 1, i.e., the upside is also referred to as “upper” or “above” and the −z-axis direction, i.e., the downside is also referred to as “lower” or “below”. Further, regarding a robot arm20, a side of a base21inFIG. 1is referred to as “proximal end” and the opposite side, i.e., a side of an end effector7is referred to as “distal end”. Furthermore, the z-axis directions inFIG. 1, i.e., upward and downward directions are referred to as “vertical directions” and the x-axis directions and the y-axis directions, i.e., leftward and rightward directions are referred to as “horizontal directions”.

A robot system100shown inFIGS. 1 and 2is an apparatus used for work of e.g. holding, transport, assembly, inspection, etc. of works including electronic components and electronic apparatuses. The robot system100includes a control apparatus1, a robot2, and the end effector7. Additionally, the robot system100includes a display device41, an input device42, etc.

The control apparatus1is placed in a position different from that of the robot2, i.e., outside of the robot2. Further, in the illustrated configuration, the robot2and the control apparatus1are electrically coupled (hereinafter, also simply referred to as “coupled”) by a cable200, however, not limited thereto the cable200may be omitted for wireless communication. That is, the robot2and the control apparatus1may be connected in wired communication or connected in wireless communication. Further, the control apparatus1may be provided inside of the base21of the robot2.

In the illustrated configuration, the robot2is a horizontal articulated robot, i.e., a SCARA robot.

As shown inFIG. 1, the robot2includes the base21, a first arm22, a second arm23, a third arm24as a working head, and a force detection unit5. The first arm22, the second arm23, and the third arm24form the robot arm20.

Further, the robot2includes a drive unit25that rotates the first arm22relative to the base21, a drive unit26that rotates the second arm23relative to the first arm22, a u-drive unit27that rotates a shaft241of the third arm24relative to the second arm23, a z-drive unit that moves the shaft241in the z-axis directions relative to the second arm23, and an angular velocity sensor29.

As described above, the robot2includes the base21rotatably supporting the robot arm20, and the robot arm20includes the first arm22and the second arm23located at the distal side of the first arm22with respect to the base21. Thereby, the movable range of the robot arm20may be increased.

As shown inFIGS. 1 and 2, the drive unit25is provided within a housing220of the first arm22, and has a motor251that generates a driving force, a reducer252that reduces the driving force of the motor251, and a position sensor253that detects the rotation angle of the rotation shaft of the motor251or the reducer252.

The drive unit26is provided within a housing230of the second arm23, and has a motor261that generates a driving force, a reducer262that reduces the driving force of the motor261, and a position sensor263that detects the rotation angle of the rotation shaft of the motor261or the reducer262.

The u-drive unit27is provided within the housing230of the second arm23, and has a motor271that generates a driving force, a reducer272that reduces the driving force of the motor271, and a position sensor273that detects the rotation angle of the rotation shaft of the motor271or the reducer272.

The z-drive unit28is provided within the housing230of the second arm23, and has a motor281that generates a driving force, a reducer282that reduces the driving force of the motor281, and a position sensor283that detects the rotation angle of the rotation shaft of the motor281or the reducer282.

As the motor251, the motor261, the motor271, and the motor281, e.g. servo motors such as AC servo motors or DC servo motors may be used.

As the reducer252, the reducer262, the reducer272, and the reducer282, e.g. planet-gear reducers, wave gearings, or the like may be used. As the position sensor253, the position sensor263, the position sensor273, and the position sensor283, e.g. angle sensors may be used.

The drive unit25, the drive unit26, the u-drive unit27, and the z-drive unit28are respectively coupled to corresponding motor drivers (not shown) and controlled by a robot control unit11of the control apparatus1via the motor drivers.

As shown inFIG. 1, the angular velocity sensor29is provided inside of the second arm23. Accordingly, the angular velocity of the second arm23may be detected. The control apparatus1performs control of the robot2based on information of the detected angular velocity.

The base21is fixed to e.g. a floor surface (not shown) by bolts or the like. The first arm22is coupled to the upper end portion of the base21. The first arm22is rotatable about a first axis O1along the vertical directions relative to the base21. When the drive unit25that rotates the first arm22is driven, the first arm22rotates about the first axis O1within the horizontal plane relative to the base21. The position sensor253may detect the amount of rotation of the first arm22relative to the base21.

The second arm23is coupled to the distal end portion of the first arm22. The second arm23is rotatable about a second axis O2along the vertical directions relative to the first arm22. The axial direction of the first axis O1and the axial direction of the second axis O2are the same. That is, the second axis O2is parallel to the first axis O1. When the drive unit26that rotates the second arm23is driven, the second arm23rotates about the second axis O2within the horizontal plane relative to the first arm22. The position sensor263may detect the amount of drive, specifically, the amount of rotation of the second arm23relative to the first arm22.

The third arm24is placed and supported in the distal end portion of the second arm23. The third arm24has the shaft241. The shaft241is rotatable about a third axis O3along the vertical directions relative to the second arm23and movable in the upward and downward directions. The shaft241is an arm at the most distal end of the robot arm20.

When the u-drive unit27that rotates the shaft241is driven, the shaft241forwardly and reversely rotates about the z-axis, that is, turns. The position sensor273may detect the amount of rotation of the shaft241relative to the second arm23.

When the z-drive unit28that moves the shaft241in the z-axis directions is driven, the shaft241moves in the upward and downward directions, i.e., the z-axis directions. The position sensor283may detect the amount of movement of the shaft241in the z-axis directions relative to the second arm23.

As described above, the robot arm20has the first arm22, the second arm23coupled to the first arm22at an opposite side to the base21and rotating about the second axis O2parallel to the first axis O1, and the third arm24supported by the second arm23and moving along an axial direction of the third axis O3in a position different from that of the second axis O2in parallel to the second axis O2. The movable range on the xy-plane may be sufficiently secured by the first arm22and the second arm23, and actuation in the z-axis directions may be performed by the third arm24.

Various end effectors are detachably coupled to the distal end portion of the shaft241. The end effectors are not particularly limited to, but include e.g. an end effector that grips an object to be transported, an end effector that processes a workpiece, an end effector used for an inspection, etc. In the embodiment, the end effector is detachably coupled. The end effector7will be described later in detail.

Note that the end effector7is not a component element of the robot2in the embodiment, however, a part or all of the end effector7may be a component element of the robot2. Further, the end effector7is not a component element of the robot arm20in the embodiment, however, a part or all of the end effector7may be a component element of the robot arm20.

As shown inFIG. 1, the end effector7has an attachment portion71attached to the shaft241, a motor72provided in the attachment portion71, and a screw limit gauge3detachably and coaxially attached to the rotation shaft of the motor72. The end effector7is detachably coupled to the distal end portion of the shaft241.

The motor72is not particularly limited, but e.g. a servo motor such as an AC servo motor or DC servo motor, stepping motor, or the like is used.

Further, the end effector7has an angle sensor (not shown) that detects the rotation angle of the rotation shaft of the motor72, and the angle sensor may detect the rotation angle of the rotation shaft of the motor72.

In the end effector7, compared to a case where a power transmission mechanism including a gear and a belt intervenes between the rotation shaft of the motor72and the screw limit gauge3, lowering of the rotation accuracy due to backlash may be suppressed.

In the embodiment, the end effector7is detachable from the robot arm20, however, not limited thereto, for example, the end effector7may be undetachable from the robot arm20.

Next, the force detection unit5will be explained.

As shown inFIGS. 1 and 3, the force detection unit5detects a force applied to the robot2, i.e., a force applied to the robot arm20and the base21. The force detection unit5is provided under the base21, i.e., at the −z-axis side and supports the base21from underneath. Accordingly, a load of the weights of the robot arm20and the base21is applied onto the force detection unit5.

Further, as shown inFIG. 3, the force detection unit5is a member in a cylindrical outer shape having a first plate51, a second plate52, a tubular portion53placed between the first plate51and the second plate52, and a plurality of, in the embodiment, four elements54. The four elements54are sandwiched between the first plate51and the second plate52. The number of the elements54is not limited to that, but may be three or less or five or more.

The first plate51and the second plate52have circular disc shapes and are sequentially placed from the +z-axis side. Note that the shapes of the first plate51and the second plate52in a plan view are not limited to the circular shapes, but may be any shapes.

The tubular portion53has a cylindrical shape in the embodiment and has a function of protecting the elements54.

The respective elements54are placed at equal intervals to form a circular shape. Thereby, forces applied to the respective elements54may be as uniform as possible and the forces may be accurately detected. Here, in this specification, a line passing through the center of a circle C on which the respective elements54are placed and being parallel to the z-axis, i.e., the first axis O1is referred to as “center line S5”. In the embodiment, the center of the force detection unit5is the center of the circle C on which the respective elements54are placed. However, when the respective elements54are not circularly placed, the geometric center of a figure with the respective elements54as vertices is referred to as the center of the force detection unit5.

As the respective elements54, elements formed using e.g. piezoelectric materials such as quartz crystal and outputting electric charge by application of external force may be employed. The control apparatus1may convert the electric charge according to an amount thereof into an external force applied to the end effector7. Such a piezoelectric material can adjust a direction to generate electric charge when an external force is applied according to the direction in which the element is placed.

In the embodiment, as shown inFIG. 4, the respective elements54may detect forces Fz of components in the vertical directions and forces Fu about the z-axis, i.e., in u-axis directions. That is, the force detection unit5detects the forces Fz in the axial direction of the third axis O3. Thereby, the work of moving the shaft241along the z-axis directions may be performed more accurately.

In the robot2, the control apparatus1is coupled via the cable200.

As shown inFIG. 2, the control apparatus1includes the robot control unit11, a motor control unit12(end effector control unit), a display control unit13, a memory unit14, and a receiving unit15, and respectively controls driving of the respective parts of the robot system100including the robot2, the motor72of the end effector7, and the display device41.

Further, the control apparatus1is configured to be respectively communicable among the robot control unit11, the motor control unit12, the display control unit13, the memory unit14, and the receiving unit15. That is, the robot control unit11, the motor control unit12, the display control unit13, the memory unit14, and the receiving unit15are coupled to one another in wired or wireless communication.

The robot control unit11controls driving of the robot2, i.e., driving of the robot arm20etc. The robot control unit11is a computer in which programs of OS etc. are installed. The robot control unit11has e.g. a CPU as a processor, a RAM, and a ROM in which the programs are stored. Further, the function of the robot control unit11may be realized by e.g. execution of various programs using the CPU.

The motor control unit12controls driving of the motor72. The motor control unit12is a computer in which programs of OS etc. are installed. The motor control unit12has e.g. a CPU as a processor, a RAM, and a ROM in which the programs are stored. Further, the function of the motor control unit12may be realized by e.g. execution of various programs using the CPU.

The display control unit13has a function of displaying various screens such as windows, characters, etc. on the display device41. That is, the display control unit13controls driving of the display device41. The function of the display control unit13may be realized by e.g. a GPU or the like.

The memory unit14has a function of storing various kinds of information including data and programs. The memory unit14stores control programs etc. The function of the memory unit14may be realized by the so-called external memory device such as a ROM.

The receiving unit15has a function of receiving input from the input device42. The function of the receiving unit15may be realized using e.g. an interface circuit. Note that, for example, when a touch panel is used, the receiving unit15has a function as an input sensing unit that senses contact of a user's finger with the touch panel or the like.

The display device41includes a monitor (not shown) formed using e.g. a liquid crystal display, EL display, or the like, and has a function of displaying various images including various screens such as windows, characters, etc.

The input device42includes e.g. a mouse, keyboard, etc. Therefore, the user operates the input device42, and thereby, may give instructions of various kinds of processing etc. to the control apparatus1.

Specifically, the user may give instructions to the control apparatus1by an operation of clicking the various screens such as windows displayed on the display device41with the mouse of the input device42and an operation of inputting characters, numerals, etc. with the keyboard of the input device42.

Note that, in the embodiment, in place of the display device41and the input device42, a display input device serving as both the display device41and the input device42may be provided. As the display input device, e.g. a touch panel such as an electrostatic touch panel or pressure-sensitive touch panel may be used. Or, the input device42may recognize sound including voice.

In the robot2, the robot arm20, the base21, and the force detection unit5have the following position relationship. As below, a position relationship among the first axis O1, a center line S2, a center line S21(first center line) of the base21, the center line S5(second center line) of the force detection unit5will be explained usingFIG. 5.

As described above, the first axis O1is a rotation axis of the first arm22coupled to the base21. Further, the first axis O1is parallel to the z-axis.

The center line S2passes through a center of gravity G of the robot2and is parallel to the z-axis, i.e., the first axis O1. The position of the center of gravity G of the robot2is displaced according to the posture of the robot arm20, and the center line S2is displaced within an area A2shown inFIG. 5. The area A2is a space having widths in the x-axis directions and the y-axis directions.

As below, the explanation will be made on the assumption that the center of gravity G of the robot2refers to a center of gravity when the robot arm20is located in a home position. As shown inFIG. 1, the home position refers to a state in which the first arm22and the second arm23extend along the y-axis at rest. In other words, the home position refers to a state in which the third axis O3is farthest from the first axis O1and a pipe8shown inFIG. 1appears as a linear shape as seen from the z-axis directions.

The center line S21of the base21is a line passing through the center of the base21and being parallel to the first axis O1. In the embodiment, the center of the base21refers to a center of gravity in a projected shape formed by projection of the base21from the z-axis directions. That is, the center refers to the geometric center of the projected shape formed by projection of the base21from the z-axis directions.

As described above, the center line S5of the force detection unit5refers to a line passing through the center of the circle on which the respective elements54are placed and being parallel to the z-axis, i.e., the first axis O1.

In the present disclosure, as shown inFIG. 5, the center line S5is located closer to the first axis O1than the center line S21. That is, the center line S5is closer to the first axis O1than the center line S21. Thereby, the following advantages are obtained.

As described above, in the robot2, the robot arm20is coupled to the position shifted from the center line S21of the base21. That is, the center line S21of the base21and the first axis O1are located in different positions. Accordingly, the center of gravity G of the robot2is located in a position shifted from the center line S21of the base21. Therefore, in the force detection unit5, inertial moment shown by an arrow inFIG. 5is generated due to the weight of the robot2itself. As a result, a force is constantly applied to the force detection unit5by the influence of the inertial moment.

In a case where the force constantly applied to the force detection unit5is a force F1, when an external force is not applied to the third arm24, the force detection unit5detects the force F1. When an external force in the direction of the arrow inFIG. 5is applied to the third arm24, a force F2is applied to the force detection unit5by the influence thereof. At the time, the force detection unit5detects a force F3as a force (F1-F2). Then, the control apparatus1controls the robot arm20based on a difference between the force F3and the force F1detected by the force detection unit5, i.e., an amount of change of the force detected by the force detection unit5.

When the force F1is larger than the force F2, the amount of change is smaller. Accordingly, for example, when the force F2is smaller, the accurate detection of the force F2may be difficult.

Accordingly, as described above, in the present disclosure, the force detection unit5is placed so that the center line S5may be closer to the first axis O1than the center line S21. Thereby, the distance between the center of gravity G of the robot2and the center line S5of the force detection unit5may be made smaller than that in related art. Therefore, the force F1constantly applied to the force detection unit5by the influence of the inertial moment as shown by the arrow inFIG. 5may be made smaller. Thus, even when the amount of change of the force detected by the force detection unit5is larger relative to the force F1and the force F2is smaller, the force F2may be accurately detected. According to the present disclosure, the detection accuracy of the force detection unit5may be improved in this way.

In the embodiment, the first axis O1and the center line S5as the second center line overlap as seen from the axial direction of the first axis O1. That is, the first axis O1and the center line S5coincide. Thereby, the inertial moment about the first axis O1generated when the first arm22rotates may be detected more accurately.

When a separation distance between the center line S21and the third axis O3is L1, a separation distance between the center line S21and the center line S5is L2, a separation distance between the center line S5and the center line S2is L3, a separation distance between the center line S21and the first axis O1is L4, and a height from the force detection unit5to the center of gravity G is L5, L1to L5preferably satisfy the following relationships.

In the robot2, L2/L1preferably satisfies 0.01≤L2/L1≤0.8 and more preferably satisfies 0.05≤L2/L1≤0.6. Thereby, the detection accuracy of the force detection unit5may be effectively improved. When L2/L1is too small, the center of gravity G shifts in a direction away from the force detection unit5, the force F1constantly applied to the force detection unit5tends to be too large, and the detection accuracy may be lower. On the other hand, when L2/L1is too large, it is harder to place the base21on the force detection unit5with balance.

Further, in the robot2, L2/L3preferably satisfies 0.1≤L2/L3≤6.0 and more preferably satisfies 0.2≤L2/L3≤4.0. Thereby, the detection accuracy of the force detection unit5may be effectively improved. When L2/L3is too small, the center of gravity G shifts in a direction away from the force detection unit5, the force F1constantly applied to the force detection unit5tends to be too large, and the detection accuracy may be lower. On the other hand, when L2/L3is too large, it is harder to place the base21on the force detection unit5with balance.

Note that, in the embodiment, L2=L4and the preferable numerical range of L4/L3is the same as the above described numerical range of L2/L3.

Furthermore, in the robot2, L2/L5preferably satisfies 0.05 L2/L53.0 and more preferably satisfies 0.1≤L2/L5≤1.0. Thereby, the detection accuracy of the force detection unit5may be effectively improved. When L2/L5is too small, the force F1constantly applied to the force detection unit5tends to be too large, and the detection accuracy may be lower. On the other hand, when L2/L5is too large, it is harder to place the base21on the force detection unit5with balance.

As described above, the robot2includes the base21, the robot arm20having the first arm22coupled to the base21and rotating about the first axis O1, and the force detection unit5provided in the base21and detecting the force acting on the base21or the robot arm20. Further, the first arm22is coupled to the base21in the position shifted from the center line S21as the first center line passing through the center of the base21and being parallel to the first axis O1. The center line S5as the second center line passing through the center of the force detection unit5and being parallel to the first axis O1is closer to the first axis O1than the center line S21as the first center line. Thereby, the distance between the center of gravity G of the robot2and the center line S5of the force detection unit5may be made smaller than that in related art. Therefore, the force F1constantly applied to the force detection unit5by the influence of the inertial moment as shown by the arrow inFIG. 5may be made smaller. Thus, even when the amount of change of the force detected by the force detection unit5is larger relative to the force F1and the external force F2is smaller, the external force F2may be accurately detected. According to the present disclosure, the detection accuracy of the force detection unit5may be improved in this way.

Second Embodiment

FIG. 6is the schematic diagram of the second embodiment of the robot according to the present disclosure.

As below, the second embodiment of the robot according to the present disclosure will be explained with reference toFIG. 6, and the explanation will be made with a focus on the differences from the above described embodiment and the explanation of the same items will be omitted.

As shown inFIG. 6, in the embodiment, the center line S5is located between the first axis O1and the center line S21as seen from the x-axis directions. That is, in a plan view of a plane containing the first axis O1and the center line S21as the first center line, the center line S5as the second center line is located between the first axis O1and the center line S21as the first center line. Thereby, the effects of the present disclosure may be obtained and the force detection unit5may be placed closer to the center portion of the base21than that of the first embodiment and the force detection unit5may support the base21more stably.

Note that, in the embodiment, the first axis O1, the center line S5, and the center line S21are located on the same plane, however, not limited thereto, these are not necessarily located on the same plane.

Third Embodiment

FIG. 7is the schematic diagram of the third embodiment of the robot according to the present disclosure.

As below, the third embodiment of the robot according to the present disclosure will be explained with reference toFIG. 7, and the explanation will be made with a focus on the differences from the above described embodiments and the explanation of the same items will be omitted.

As shown inFIG. 7, in the embodiment, the center line S5is located between the center line S2and the first axis O1as seen from the x-axis directions. That is, in the plan view of the plane containing the first axis O1and the center line S21as the first center line, the center line S5as the second center line passes through the center of gravity G of the robot2and is located between the center line S2as the line parallel to the first axis O1and the first axis O1. Thereby, the effects of the present disclosure may be obtained and the force F1constantly applied to the force detection unit5by the influence of the inertial moment as shown by an arrow inFIG. 7may be made smaller because the center line S5is closer to the center line S2than those in the above described respective embodiments.

Note that, in the embodiment, the first axis O1, the center line S5, and the center line S21are located on the same plane, however, not limited thereto, these are not necessarily located on the same plane.

As above, the robot according to the present disclosure is explained based on the illustrated embodiments, however, the present disclosure is not limited to those. The configurations of the respective parts may be replaced by arbitrary configurations having the same functions. Further, another arbitrary configuration may be added. Furthermore, the features of the respective embodiments may be combined.

In the above described embodiments, the number of rotation axes of the robot arm is three, however, the number is not limited to that in the present disclosure. The number of rotation axes of the robot arm may be e.g. two, four, or more. That is, in the above described embodiments, the number of arms is three, however, the number is not limited to that in the present disclosure. The number of arms may be e.g. two, four, or more.