Detection method, robot system, and program

Abstract

To provide a detection method, a robot system, and a program capable of detecting an overload state of a shaft.SOLUTION: A detection method includes: a first step of acquiring force F in a direction orthogonal to a third rotational axis acting on a shaft by a rotational operation of a first arm or a second arm; a second step of acquiring bending force F1 applied to a predetermined portion of the shaft on the basis of the force F acquired in the first step; a third step of comparing maximum bending force F0 allowable by the predetermined portion of the shaft with the bending force F1 acquired in the second step; and a fourth step of giving notification of an overloaded state of the shaft when a comparison result in the third step is F1≥F0.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a detection method, a robot system, and a program.

Background Art

[0002] A horizontally articulated robot including a support arm, a first arm rotatably connected to the support arm, a second arm rotatably connected to the first arm, and a shaft which is rotatably connected to the second arm and is vertically movable with respect to the second arm is known.

[0003] Further, this horizontally articulated robot includes a motor for rotating the first arm with respect to the support arm, a motor for rotating the second arm with respect to the first arm, a motor for rotating the third arm with respect to the second arm, and a motor for vertically moving the third arm with respect to the second arm.

[0004] In Patent Document 1, a torque limit value is set for each motor, and by restricting the output torque of each motor so as not to exceed the torque limit value, overload on each arm and each motor is prevented, and damage is prevented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the configuration described in Patent Document 1, the overload on the third arm, particularly the overload caused by the bending stress acting on the third arm due to the rotation of the first arm and the second arm, is not considered. As a result, if the rotation speeds of the first arm and the second arm are too high, there is a risk of overloading the third arm. On the other hand, if the rotation speeds of the first arm and the second arm are reduced so as not to cause an overload on the third arm, there is a risk of reducing the working efficiency. Therefore, it has been difficult to increase the working efficiency while preventing damage to the third arm.

Means for Solving the Problem

[0007] The detection method of the present invention is a detection method for detecting an overload state of a shaft in a robot having a base, a first arm rotatably connected to the base about a first rotation axis, a second arm rotatably connected to the first arm about a second rotation axis parallel to the first rotation axis, and a shaft rotatably connected to the second arm about a third rotation axis parallel to the first rotation axis and movable along the third rotation axis, comprising: a first step of obtaining a force F in a direction orthogonal to the third rotation axis acting on the shaft by a rotational operation of the first arm or the second arm; a second step of obtaining a bending stress F1 applied to a predetermined portion of the shaft based on the force F obtained in the first step; a third step of comparing a maximum bending stress F0 that the predetermined portion of the shaft can withstand with the bending stress F1 obtained in the second step; a fourth step of notifying an overload state of the shaft when the comparison result in the third step is F1≧F0.

[0008] The robot system of the present invention includes a base, a first arm rotatably connected to the base about a first rotation axis, a second arm rotatably connected to the first arm about a second rotation axis parallel to the first rotation axis, a shaft rotatably connected to the second arm about a third rotation axis parallel to the first rotation axis and movable along the third rotation axis, and a detection unit that detects a force or acceleration acting on the shaft. It is provided with a control device for controlling the operation of the robot. The control device Based on the detection value of the detection unit, a first acquisition unit that acquires a force F in a direction orthogonal to the third rotation axis acting on the shaft by the rotational movement of the first arm or the second arm. A second acquisition unit that acquires a bending stress F1 applied to a predetermined portion of the shaft based on the force F acquired by the first acquisition unit. A comparison unit that compares the maximum bending stress F0 that the predetermined portion of the shaft can withstand with the bending stress F1 acquired by the second acquisition unit. When the comparison result by the comparison unit is F1≧F0, it has a notification signal generation unit that generates a notification signal for notifying the overload state of the shaft.

[0009] The program of the present invention is a program for detecting an overload state of the shaft in a robot having a base, a first arm rotatably connected to the base about a first rotation axis, a second arm rotatably connected to the first arm about a second rotation axis parallel to the first rotation axis, a shaft rotatably connected to the second arm about a third rotation axis parallel to the first rotation axis and movable along the third rotation axis, and includes A first step of acquiring a force F in a direction orthogonal to the third rotation axis acting on the shaft by the rotational movement of the first arm or the second arm. A second step of acquiring a bending stress F1 applied to a predetermined portion of the shaft based on the force F acquired in the first step. A third step of comparing the maximum bending stress F0 that the predetermined part of the shaft can withstand with the bending stress F1 obtained in the second step; When the comparison result in the third step is F1≧F0, it is for executing a fourth step of notifying an overload state of the shaft.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0011] Hereinafter, the detection method, robot system, and program of the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0012] <First Embodiment> FIG. 1 is a schematic configuration diagram of a robot system according to a first embodiment of the present invention. FIG. 2 is a block diagram of the robot system shown in FIG. 1. FIG. 3 is a cross-sectional view of a shaft provided in the robot shown in FIG. 1. FIG. 4 is a side view of the lower end portion of the shaft provided in the robot shown in FIG. 1. FIG. 5 is a flowchart for explaining an example of the detection method of the present invention.

[0013] Note that the vertical direction in Fig. 1 coincides with the plumb direction. The upper side in Fig. 1 is also referred to as "upper", and the lower side as "lower". For the robot arm 72, the first arm 73, and the second arm 74, the right side in Fig. 1 is referred to as the "base end portion", and the left side as the "tip end portion".

[0014] Also, for convenience of explanation, in Figs. 1, 3, and 4, the X-axis, Y-axis, and Z-axis are illustrated as three orthogonal axes. On each axis, the tip end side of the arrow is defined as "+", and the opposite side as "-". Also, the +Z-axis direction in Figs. 1, 3, and 4, that is, the upper side, is also referred to as "upper", and the -Z-axis direction, that is, the lower side, is also referred to as "lower". Further, the Z-axis direction in Figs. 1, 3, and 4, that is, the vertical direction, is defined as the "plumb direction", and the X-axis direction and Y-axis direction, that is, the horizontal direction, are defined as the "horizontal direction".

[0015] Also, in this specification, "plumb" means not only the case where it coincides with the plumb, but also the case where it is inclined slightly with respect to the plumb, for example, within ±10°. Also, in this specification, "parallel" means not only the case where two objects coincide with being parallel, but also the case where they are inclined slightly from parallel, for example, within ±10°.

[0016] The robot system 1 shown in Fig. 1 executes the detection method of the present invention and includes a robot 7 and a control device 3 that controls the driving of each part of the robot 7.

[0017] The robot 7 in the present embodiment is a scalar robot and is used, for example, in various operations such as holding, transporting, assembling, processing, and inspecting workpieces such as electronic components. However, the uses and types of operations of the robot 7 are not limited to the above. Also, the robot 7 only needs to be provided with a spline shaft and may be a robot other than a scalar robot.

[0018] As shown in FIG. 1, the robot 7 has a base 71 and a robot arm 72 rotatably connected to the base 71. The robot arm 72 has a first arm 73 whose base end is connected to the base 71 and rotates about a first rotation axis J1 along the vertical direction with respect to the base 71, and a second arm 74 whose base end is connected to the tip of the first arm 73 and rotates about a second rotation axis J2 along the vertical direction with respect to the first arm 73.

[0019] A work head 75 is provided at the tip of the second arm 74. The work head 75 has a spline nut 751 and a ball screw nut 752 coaxially arranged at the tip of the second arm 74, and a spline shaft 753 inserted through the spline nut 751 and the ball screw nut 752. The spline shaft 753 is rotatable about a third rotation axis J3 which is its central axis and along the vertical direction with respect to the second arm 74, and is movable along the third rotation axis J3, that is, it is a shaft that can move up and down. This spline shaft 753 is also referred to as a third arm.

[0020] A detection unit 2 for detecting the force or acceleration acting on the spline shaft 753 is installed at the lower end 754 of the spline shaft 753 in the vertical direction. In this embodiment, the detection unit 2 has a force sensor 21 for detecting the force acting on the spline shaft 753.

[0021] In this embodiment, the force sensor 21 is a six-axis force sensor. The force sensor 21 detects the magnitude of the force on three detection axes perpendicular to each other and the magnitude of the torque about the three detection axes. That is, it detects the force components in the axial directions of the X-axis, Y-axis, and Z-axis perpendicular to each other, the force component in the direction Tx about the X-axis, the force component in the direction Ty about the Y-axis, and the force component in the direction Tz about the Z-axis. In this embodiment, the Z-axis direction is the vertical direction. Also, the force sensor 21 is not limited to a six-axis force sensor and may have other configurations.

[0022] As shown in FIG. 2, the force sensor 21 is electrically connected to the control device 3 and transmits to the control device 3 at any time a signal indicating the magnitude and direction of the detected force. Based on these signals, the control device 3 calculates the bending stress acting in the horizontal direction, that is, in an arbitrary direction on the x-y plane. This will be described in detail later.

[0023] An end effector 76 is attached to the lower end of the force sensor 21. The end effector 76 is detachable from the spline shaft 753, and an appropriate one suitable for the target work is selected as appropriate.

[0024] As shown in FIG. 4, in the present embodiment, the end effector 76 has a configuration including a hand 761, a tool 762, and a support portion 763 that supports these. The support portion 763 extends in the X-axis direction. The hand 761 and the tool 762 are supported at both ends of the support portion 763. The hand 761 and the tool 762 are located on opposite sides via the third rotation axis J3.

[0025] Further, since the hand 761 is heavier than the tool 762, the center of gravity G of the end effector 76 is shifted in the +X-axis direction from the third rotation axis J3.

[0026] Note that the end effector 76 is not limited to the illustrated configuration, and may have a configuration in which the center of gravity G overlaps with the third rotation axis J3.

[0027] The robot 7 has a first joint portion 4K that rotatably connects the base 71 and the first arm 73, and a motor unit 4 that rotates the first arm 73 around the first rotation axis J1 with respect to the base 71 is installed in the first joint portion 4K.

[0028] Further, the robot 7 has a second joint portion 6K that rotatably connects the first arm 73 and the second arm 74, and a motor unit 6 that rotates the second arm 74 around the second rotation axis J2 with respect to the first arm 73 is installed in the second joint portion 6K.

[0029] In addition, the robot 7 includes a first drive mechanism 791 that rotates the spline nut 751 to rotate the spline shaft 753 around the third rotation axis J3, and a second drive mechanism 792 that rotates the ball screw nut 752 to move the spline shaft 753 in the direction along the third rotation axis J3, that is, in the vertical direction. The second drive mechanism 792 is installed below the first drive mechanism 791. The first drive mechanism 791 has a motor 793, and the second drive mechanism 792 has a motor 794. As shown in FIG. 2, the motors 793 and 794 are electrically connected to the control device 3. The energization conditions such as the energization pattern, energization timing, and energization amount to the motors 793 and 794 are controlled by the control device 3.

[0030] The motor unit 4 includes a motor 41 and a power transmission mechanism (not shown) including, for example, a speed reducer. The motor unit 6 includes a motor 61 and a power transmission mechanism (not shown) including, for example, a speed reducer.

[0031] The motor 41 generates a driving force for rotating the first arm 73 with respect to the base 71. The motor 61 generates a driving force for rotating the second arm 74 with respect to the first arm 73. The motors 41 and 61 are not particularly limited, but are preferably servo motors such as AC servo motors and DC servo motors, for example.

[0032] As shown in FIG. 2, the motors 41 and 61 are electrically connected to the control device 3. Although not shown, the motors 41 and 61 each include a stator, a rotor that rotates inside the stator, and a case that houses them. The stator is arranged along the inner circumference of the case and has a winding such as a three-phase winding, for example. The stator generates a magnetic field by energizing the winding, for example, by applying three-phase alternating current. In the motors 41 and 61, the energization pattern, energization timing, energization amount, etc. to each winding provided in the stator are controlled by the control device 3.

[0033] In addition, motors 793, 794, 41, and 61 each incorporate a motor driver (not shown).

[0034] Note that motors 793 and 794 may be the same as motors 41 and 61, or they may be motors with different types and configurations.

[0035] The power transmission mechanisms provided in motor units 4 and 6 transmit the driving force of motors 41 and 61, which are power sources, to adjacent first arm 73 and second arm 74, and have, for example, at least one of a speed reducer, a pulley, an endless belt, etc. The speed reducer is not particularly limited, and a speed reducer such as an eccentric swing type, a planetary gear type, or a harmonic gear type can be used.

[0036] As shown in FIG. 2, control device 3 includes a control unit 31, a storage unit 32, and a communication unit 33. These units are connected to be communicable with each other via, for example, a bus.

[0037] Control unit 31 is composed of, for example, at least one CPU (Central Processing Unit), reads out and executes various programs such as operation programs stored in storage unit 32. The signal generated by control unit 31 is transmitted to each part of robot 7 via communication unit 33, and the signal from each part of robot 7 is received by control unit 31 via communication unit 33. Thereby, robot arm 72 can execute a predetermined operation under predetermined conditions.

[0038] In addition, the program of the present invention for executing the detection method of the present invention is stored in storage unit 32. By control unit 31 reading out and executing the program of the present invention, the detection method of the present invention can be executed.

[0039] The storage unit 32 stores various programs and the like executed by the control unit 31. Examples of the storage unit 32 include a configuration having a volatile memory such as a RAM (Random Access Memory), a non-volatile memory such as a ROM (Read Only Memory), a removable external storage device, and the like.

[0040] The communication unit 33 transmits and receives signals between the control device 3 and the robot 7 or external devices using an external interface such as a wired LAN (Local Area Network) or a wireless LAN. In this case, communication may be performed via a server (not shown), or communication may be performed via a network such as the Internet.

[0041] As shown in FIG. 2, the control unit 31 includes, as functional units, a first acquisition unit 311, a second acquisition unit 312, a comparison unit 313, and a notification signal generation unit 314.

[0042] The first acquisition unit 311 is a part that executes the first step, and based on the detection value of the detection unit 2, acquires the force F (N) acting on the spline shaft 753 by the rotational movement of the first arm 73 or the second arm 74. The force F (N) is a force acting in the horizontal direction and in the direction opposite to the direction in which the spline shaft 753 accelerates in the horizontal direction, and is a force acting in the direction of bending the spline shaft 753.

[0043] In the following description, a case where only the first arm 73 rotates in a state where the first arm 73 and the second arm 74 extend linearly will be described.

[0044] For example, when the spline shaft 753 accelerates in the direction of the arrow (F) in FIG. 3, due to the action of inertial force, the force sensor 21 outputs the component Fx (N) of the inertial force in the X-axis direction and the component Fy (N) of the inertial force in the Y-axis direction.

[0045] Based on the components Fx(N) and Fy(N), the first acquisition unit 311 calculates the force F(N), which is the synthesized component. Specifically, the following formula (1) is calculated.

[0046]

Equation

[0047] Thereby, the first acquisition unit 311 can acquire the force F(N). Note that the formula (1) is stored in the storage unit 32 in advance.

[0048] The second acquisition unit 312 is the part that executes the second step. Based on the force F acquired by the first acquisition unit 311, it acquires the bending stress F1 (N / mm 2 ) applied to a predetermined part of the spline shaft 753. In this embodiment, the predetermined part of the spline shaft 753 is the lower part of the part supported by the ball screw nut 752 among the spline shafts 753. However, it is not limited to this configuration, and other parts of the spline shaft 753 may also be used. Hereinafter, the predetermined part will be referred to as "part 200".

[0049] Specifically, the second acquisition unit 312 divides the value (L×F) obtained by multiplying the force F(N) acquired by the first acquisition unit 311 by the distance L(mm) between the center of gravity G of the end effector and the part 200 by the section modulus C(mm 3 ) of the cross section of the part 200 to calculate the bending stress F1 (N / mm 2 ). That is, the following formula (2) is calculated.

[0050] F1=(L×F) / C…(2)

[0051] Thereby, the second acquisition unit 312 can acquire the bending stress F1 (N / mm 2 ). Note that the formula (2), the distance L(mm) between the center of gravity G of the end effector 76 and the part 200, and the section modulus C(mm 3 ) are stored in the storage unit 32 in advance.

[0052] As shown in FIG. 4, the distance L (mm) is a value obtained by considering the displacement amount d of the position of the center of gravity G of the end effector 76 with respect to the third rotation axis J3. Since the position of the center of gravity G of the end effector 76 and the displacement amount d are known for each type of end effector to be mounted, the distance L can be obtained in advance. In this way, the second acquisition unit 312 acquires the bending stress F1 while further considering the displacement amount d of the position of the center of gravity G of the end effector 76 with respect to the third rotation axis J3. Thereby, the bending stress F1 can be accurately acquired regardless of the position of the center of gravity G of the end effector 76.

[0053] The comparison unit 313 is a part that executes the third step, and compares the maximum bending stress F0, which is a threshold value, with the bending stress F1 acquired by the second acquisition unit 312. The maximum bending stress F0 is the value of the maximum bending stress that the portion 200 of the spline shaft 753 can tolerate, and is stored in the storage unit 32 in advance. Note that the maximum bending stress F0 may be a value slightly lower than the design value of the bending stress. Hereinafter, a state where F1≧F0 is referred to as an overload state of the spline shaft 753.

[0054] The notification signal generation unit 314 is a part that executes the fourth step. When the comparison result by the comparison unit 313 is F1≧F0, the notification signal generation unit 314 generates a notification signal for notifying the overload state of the spline shaft 753. There are, for example, the following three patterns in the notification signal generated by the notification signal generation unit 314. Note that two or more of the following patterns 1, 2, and 3 may be combined.

[0055] (Pattern 1) The robot system 1 has a voice generation unit (not shown), such as a speaker, that notifies by voice, and the notification signal generated by the notification signal generation unit 314 is a drive signal for driving the voice generation unit.

[0056] (Pattern 2) The robot system 1 has a display unit (not shown), such as a liquid crystal display, for visual notification, and the notification signal generated by the notification signal generation unit 314 is a drive signal for driving the display unit.

[0057] (Pattern 3) Notification can be made by reducing the speed of the robot arm 72. In this case, the notification signal generated by the notification signal generation unit 314 is a drive signal for driving the motors 41 and 61.

[0058] In this way, in the robot system 1, the bending stress F1 acting on the spline shaft 753 is obtained by the rotational movement of the first arm 73 or the second arm 74. When the bending stress F1 reaches the maximum bending stress F0, the overload state of the spline shaft 753 can be notified. As a result, the overload state of the spline shaft 753 can be grasped. Therefore, for example, when the spline shaft 753 is not in an overload state, by operating the robot 7, the operating speed of the robot 7 can be effectively increased until the spline shaft 753 enters an overload state. When the spline shaft 753 enters an overload state, the robot 7 can be operated to eliminate the overload state. As a result, it is possible to prevent damage to the spline shaft 753 and improve the working efficiency by increasing the rotational speed of the first arm 73 and the second arm 74 as fast as possible.

[0059] In particular, the hollowness ratio of the cross section of the spline shaft 753 often varies depending on the model and type of the robot. Therefore, instead of simply judging whether it is in an overload state using only the force F, a configuration is adopted in which the bending stress F1 derived from the force F and other factors is used to judge whether it is in an overload state, so that a more appropriate judgment of the overload state considering the hollowness ratio of the cross section of the spline shaft 753 can be made.

[0060] As described above, the robot system 1 includes a robot 7 having a base 71, a first arm 73 rotatably connected to the base 71 about a first rotation axis J1, a second arm 74 rotatably connected to the first arm 73 about a second rotation axis J2 parallel to the first rotation axis J1, a spline shaft 753 which is a shaft rotatable about a third rotation axis J3 parallel to the first rotation axis J1 and movably connected to the second arm 74 along the third rotation axis J3, and a detection unit 2 that detects a force or acceleration acting on the spline shaft 753, and a control device 3 that controls the operation of the robot 7. Further, based on the detection value of the detection unit 2, the control device 3 includes a first acquisition unit 311 that acquires a force F in a direction orthogonal to the third rotation axis J3 acting on the spline shaft 753 by a rotational operation of the first arm 73 or the second arm 74, a second acquisition unit 312 that acquires a bending stress F1 applied to a part 200 which is a predetermined part of the spline shaft 753 based on the force F acquired by the first acquisition unit 311, a comparison unit 313 that compares a maximum bending stress F0 that the part 200 of the spline shaft 753 can withstand with the bending stress F1 acquired by the second acquisition unit 312, and a notification signal generation unit 314 that generates a notification signal for notifying an overload state of the spline shaft 753 when the comparison result by the comparison unit 313 is F1≧F0. Thereby, the overload state of the spline shaft 753 can be grasped. Therefore, it is possible to improve the working efficiency while preventing damage to the spline shaft 753.

[0061] In addition, in the present embodiment, the case where only the first arm 73 rotates when the first arm 73 and the second arm 74 extend linearly has been described. However, the present invention is not limited to this, and the force F and the bending stress F1 can be acquired even when the first arm 73 and the second arm 74 do not extend linearly. Further, in the present invention, when only the second arm 74 rotates, or when both the first arm 73 and the second arm 74 rotate in the same direction or in opposite directions, the force F and the bending stress F1 can be acquired.

[0062] Next, an example of the detection method of the present invention will be described with reference to the flowchart shown in FIG. 5.

[0063] First, in step S101, the robot arm 72 is driven based on a pre-specified operation program. That is, the control unit 31 reads and executes the operation program stored in the storage unit 32.

[0064] Next, in step S102, the force F is acquired. That is, the first acquisition unit 311 acquires the force F (N) acting on the spline shaft 753 due to the rotational movement of the first arm 73 or the second arm 74 based on the detection value of the detection unit 2. Specifically, the first acquisition unit 311 acquires the components Fx (N) and Fy (N) which are the output values of the force sensor 21, and calculates the above formula (1). Thereby, the force F (N) can be acquired. Note that the formula (1) is stored in the storage unit 32 in advance. Such step S102 is the first step.

[0065] Next, in step S103, the bending stress F1 is acquired. That is, the second acquisition unit 312 acquires the bending stress F1 (N / mm 2 ) applied to the portion 200 of the spline shaft 753 based on the force F acquired in step S102. Specifically, the second acquisition unit 312 calculates the above formula (2) using the force F (N) acquired by the first acquisition unit 311, the distance L (mm) between the center of gravity G of the end effector and the portion 200, and the section modulus C (mm 3 ). Thereby, the bending stress F1 (N / mm 2 ) can be calculated. This step is the second step.

[0066] Note that as described above, the second acquisition unit 312 further considers the deviation amount d of the center of gravity G of the end effector 76 with respect to the third rotation axis J3 to acquire the bending stress F1. Thereby, the bending stress F1 can be accurately acquired regardless of the position of the center of gravity G of the end effector 76.

[0067] Next, in step S104, it is determined whether F1 ≥ F0. That is, the comparison unit 313 compares the maximum bending stress F0 that the portion 200 of the spline shaft 753 can tolerate with the bending stress F1 obtained in step S103, and determines whether F1 ≥ F0. This step is the third step.

[0068] In step S104, if it is determined that F1 ≥ F0 (YES), the process proceeds to step S105. On the other hand, in step S104, if it is determined that F1 < F0 (NO), the process proceeds to step S106.

[0069] In step S105, the notification signal generation unit 314 generates a notification signal and executes notification based on this notification signal. That is, the notification signal generation unit 314 generates and outputs a notification signal for notifying the overload state of the spline shaft 753, and executes notification based on the notification signal. Examples of the type of the notification signal and the method of notification include the aforementioned patterns 1, 2, 3, and combinations thereof. This step is the fourth step.

[0070] Next, in step S106, the control unit 31 determines whether the execution of the operation program has been completed. In step S106, if it is determined that the execution of the operation program has been completed, the process ends. If it is determined that the execution of the operation program has not been completed, the process returns to step S102 and the subsequent steps are repeated.

[0071] As described above, the detection method of the present invention is a detection method for detecting an overload state of a spline shaft 753 in a robot 7 having a base 71, a first arm 73 rotatably connected to the base 71 around a first rotation axis J1, a second arm 74 rotatably connected to the first arm 73 around a second rotation axis J2 parallel to the first rotation axis J1, and a spline shaft 753 which is a shaft rotatably around a third rotation axis J3 parallel to the first rotation axis J1 and movably along the third rotation axis J3 and connected to the second arm 74. The detection method includes: a first step of obtaining a force F in a direction orthogonal to the third rotation axis J3 acting on the spline shaft 753 by a rotational operation of the first arm 73 or the second arm 74; a second step of obtaining a bending stress F1 applied to a site 200 which is an example of a predetermined site of the spline shaft 753 based on the force F obtained in the first step; a third step of comparing a maximum bending stress F0 that the site 200 of the spline shaft 753 can tolerate with the bending stress F1 obtained in the second step; and a fourth step of notifying an overload state of the spline shaft 753 when the comparison result in the third step is F1≧F0. Thereby, the overload state of the spline shaft 753 can be grasped. Therefore, it is possible to improve the working efficiency while preventing damage to the spline shaft 753.

[0072] In the second step, the bending stress F1 is calculated based on the force F and a section modulus C of a site 200 which is an example of a predetermined site of the spline shaft 753. Thereby, the bending stress F1 can be accurately obtained. In particular, since the section modulus of the spline shaft 753 often varies depending on the model and type of the robot, with the above configuration, the bending stress F1 can be accurately obtained for many models and types of robots.

[0073] In the first step, the force F is obtained based on a detection value of a force sensor 21 provided at an end portion 754 which is a lower end portion in the vertical direction of the spline shaft 753. Thereby, the force F can be directly and accurately detected.

[0074] In the second step, the bending stress F1 is obtained by further considering the deviation amount d of the position of the center of gravity G of the end effector 76 with respect to the third rotation axis J3. As a result, the bending stress F1 can be accurately obtained regardless of the position of the center of gravity G of the end effector 76.

[0075] The program of the present invention is a program for detecting an overload state of a spline shaft 753 in a robot 7 having a base 71, a first arm 73 rotatably connected to the base 71 around a first rotation axis J1, a second arm 74 rotatably connected to the first arm 73 around a second rotation axis J2 parallel to the first rotation axis J1, and a spline shaft 753 which is a shaft rotatably around a third rotation axis J3 parallel to the first rotation axis J1 and movably along the third rotation axis J3 and connected to the second arm 74. The program includes: a first step of obtaining a force F in a direction orthogonal to the third rotation axis J3 acting on the spline shaft 753 by a rotational operation of the first arm 73 or the second arm 74; a second step of obtaining a bending stress F1 applied to a part 200 which is an example of a predetermined part of the spline shaft 753 based on the force F obtained in the first step; a third step of comparing the maximum bending stress F0 that the part 200 of the spline shaft 753 can withstand with the bending stress F1 obtained in the second step; and a fourth step of notifying an overload state of the spline shaft 753 when the comparison result in the third step is F1 ≧ F0. By executing such a program, the overload state of the spline shaft 753 can be grasped. Therefore, it is possible to improve the working efficiency while preventing damage to the spline shaft 753.

[0076] Note that, in the present embodiment, the program of the present invention is stored in the storage unit 32, but the present invention is not limited thereto, and it may be stored in other storage devices, storage media, etc.

[0077] <Second Embodiment> FIG. 6 is a block diagram of a robot system according to a second embodiment of the present invention.

[0078] Next, a second embodiment of the detection method, robot system, and program of the present invention will be described with reference to FIG. 6. The description will focus on the differences from the first embodiment described above, and the description of the same matters will be omitted.

[0079] As shown in FIG. 6, the detection unit 2 includes an acceleration sensor 22. The acceleration sensor 22 is provided at the lower end 754 in the vertical direction of the spline shaft 753 instead of the force sensor 21 shown in FIG. 1.

[0080] The acceleration sensor 22 detects the inertial force generated by the rotation of the first arm 73 and the second arm 74. In this embodiment, the acceleration sensor 22 includes six types in total: the acceleration in the direction along the X-axis, the acceleration in the direction along the Y-axis, the acceleration in the direction along the Z-axis, the angular velocity in the direction Tx around the axis of the X-axis, the angular velocity in the direction Ty around the axis of the Y-axis, and the angular velocity in the direction Tz around the axis of the Z-axis. That is, the acceleration sensor 22 is an IMU (Inertial Measurement Unit) that detects the acceleration in three mutually perpendicular axial directions and the angular velocity around the axis of the third rotation axis J3.

[0081] As shown in FIG. 6, the acceleration sensor 22 is electrically connected to the control device 3 and transmits a signal of the detected value indicating the detected inertial force to the control device 3 at any time. The first acquisition unit 311 calculates the force F acting in an arbitrary direction on the x-y plane using the acceleration in the direction along the X-axis and the acceleration in the direction along the Y-axis.

[0082] Let the weight of the end effector 76 be M (kg), and the acceleration in the direction along the X-axis be Ax (m / s 2 ), and the acceleration in the direction along the Y-axis be Ay (m / s 2 ). When this is the case, the component Fx of the force F in the direction along the X-axis direction can be obtained by the following formula (3), and the component Fy in the direction along the Y-axis direction can be obtained by the following formula (4).

[0083] Fx = Ax × M...(3) Fy = Ay × M...(4)

[0084] In the first acquisition unit 311, in the first step, by calculating the above formulas (3) and (4), the component Fx in the direction along the X-axis of the force F and the component Fy in the direction along the Y-axis of the force F can be obtained. Then, by substituting these values into the formula (1) described in the first embodiment, the first acquisition unit 311 can acquire the force F (N) obtained by synthesizing the component Fx and the component Fy. Note that the formulas (3) and (4) are stored in the storage unit 32 in advance.

[0085] Since the method for acquiring the bending stress F1 acquired by the second acquisition unit 312, the comparison method of the comparison unit 313, and the generation of the notification signal by the notification signal generation unit 314 and the method of notification are the same as those in the first embodiment, the description thereof is omitted.

[0086] As described above, in this embodiment, in the first step, based on the detection value of the acceleration sensor 22 provided at the lower end portion 754 in the vertical direction of the spline shaft 753 and the weight M of the end effector 76 attached to the spline shaft 753, the force F is acquired. Thereby, the force F can be accurately detected.

[0087] When the end effector 76 is configured to grip a workpiece, it is preferable to perform the above calculation including the gripped workpiece in the weight of the end effector 76.

[0088] <Third Embodiment> FIG. 7 is a block diagram of a robot system according to the third embodiment of the present invention.

[0089] Hereinafter, the third embodiment of the detection method, the robot system, and the program of the present invention will be described with reference to FIG. 7. The description will focus on the differences from the first embodiment described above, and the description of the same matters will be omitted.

[0090] As shown in FIG. 7, the detection unit 2 has an acceleration calculation unit 23 instead of the force sensor 21. The acceleration calculation unit 23 is composed of, for example, at least one CPU (Central Processing Unit), and reads and executes various programs such as an operation program stored in a storage unit (not shown). The acceleration calculation unit 23 may be configured to be implemented as one of the program functions executed by the control device 3.

[0091] By executing the program, the acceleration calculation unit 23 calculates the acceleration Ax (m / s 2 ) in the direction along the X-axis and the acceleration Ay (m / s 2 ) in the direction along the Y-axis of the spline shaft 753. When the weight of the end effector 76 is M (kg), the rotating arm length is R (mm), the angular velocity is W (rad / s), and the angular acceleration is WA (rad / s 2 ), the component Fx of the force F in the direction along the X-axis can be obtained by the following formula (5), and the component Fy in the direction along the Y-axis can be obtained by the following formula (6).

[0092] Fx = R × W × W × M... (5) Fy = R × WA × M... (6)

[0093] In the first step, the first acquisition unit 311 can obtain the component Fx of the force F in the direction along the X-axis and the component Fy of the force F in the direction along the Y-axis by calculating the above formulas (5) and (6). Then, by substituting these values into the formula (1) described in the first embodiment, the first acquisition unit 311 can obtain the force F (N) obtained by synthesizing the component Fx and the component Fy. Note that the formulas (5) and (6) are stored in the storage unit 32 in advance.

[0094] Since the method for obtaining the bending stress F1 acquired by the second acquisition unit 312, the comparison method of the comparison unit 313, and the generation of the notification signal by the notification signal generation unit 314 and the method of notification are the same as those in the first embodiment, the description thereof is omitted.

[0095] Thus, in this embodiment, in the first step, the force F is obtained based on the acceleration calculated by the acceleration calculation unit 23 and the weight M of the end effector 76 attached to the spline shaft 753. Thereby, even in a configuration without using a sensor, the force F can be detected.

[0096] As described above, the detection method, the robot system, and the program of the present invention have been described based on the illustrated embodiments. However, the present invention is not limited to these, and the configurations of the respective parts in the detection method, the robot system, and the program can be replaced with any configurations having the same functions and steps. Further, any other arbitrary components and steps may be added to the detection method, the robot system, and the program.

[0097] Also, the detection method, the robot system, and the program of the present invention may be a combination of the features of the respective embodiments.

Explanation of Reference Numerals

[0098] 1... Robot system, 2... Detection unit, 3... Control device, 4... Motor unit, 4K... First joint part, 6... Motor unit, 6K... Second joint part, 7... Robot, 21... Force sensor, 22... Acceleration sensor, 23... Acceleration calculation unit, 31... Control part, 32... Memory part, 33... Communication part, 41... Motor, 61... Motor, 71... Base, 72... Robot arm, 73... First arm, 74... Second arm, 75... Working head, 76... End effector, 200... Part, 311... First acquisition part, 312... Second acquisition part, 313... Comparison part, 314... Notification signal generation part, 751... Spline nut, 752... Ball screw nut, 753... Spline shaft, 754... End part, 761... Hand, 762... Tool, 763... Support part, 791... First drive mechanism, 792... Second drive mechanism, 793... Motor, 794... Motor, d... Deviation amount, F... Force, Fx... Component, Fy... Component, G... Center of gravity, J1... First rotation axis, J2... Second rotation axis, J3... Third rotation axis, L... Distance, S101... Step, S102... Step, S103... Step, S104... Step, S105... Step, S106... Step, Tx... Direction, Ty... Direction, Tz... Direction

Claims

1. A detection method for detecting an overload state of a shaft in a robot having a base, a first arm rotatably connected to the base about a first rotation axis, a second arm rotatably connected to the first arm about a second rotation axis parallel to the first rotation axis, and a shaft rotatably connected to the second arm about a third rotation axis parallel to the first rotation axis and movable along the third rotation axis, comprising: A first step of obtaining a force F in a direction orthogonal to the third rotation axis acting on the shaft by a rotational operation of the first arm or the second arm; A second step of obtaining a bending stress F1 applied to a predetermined portion of the shaft based on the force F obtained in the first step; A third step of comparing a maximum bending stress F0 that the predetermined portion of the shaft can withstand with the bending stress F1 obtained in the second step; A fourth step of notifying an overload state of the shaft when the comparison result in the third step is F1≧F0. The detection method is characterized by including the above steps.

2. The detection method according to claim 1, wherein in the second step, the bending stress F1 is calculated based on the force F and a section modulus of the predetermined portion of the shaft.

3. The detection method according to claim 1 or 2, wherein in the first step, the force F is obtained based on a detection value of a force sensor provided at a lower end portion of the shaft in the vertical direction.

4. The detection method according to claim 1 or 2, wherein in the first step, the force F is obtained based on a detection value of an acceleration sensor provided at a lower end portion of the shaft in the vertical direction and a weight of an end effector attached to the shaft.

5. The detection method according to claim 4, wherein in the second step, the bending stress F1 is obtained by further considering a deviation amount of the position of the center of gravity of the end effector with respect to the third rotation axis.

6. The detection method according to claim 1 or 2, wherein in the first step, the force F is obtained based on an acceleration of the shaft calculated and a weight of an end effector attached to the shaft.

7. A base, a first arm rotatably connected to the base about a first rotation axis, a second arm rotatably connected to the first arm about a second rotation axis parallel to the first rotation axis, a shaft rotatably connected to the second arm about a third rotation axis parallel to the first rotation axis and movable along the third rotation axis, and a detection unit for detecting a force or acceleration acting on the shaft, a robot having the above components, A control device for controlling the operation of the robot, The control device, A first acquisition unit that acquires a force F in a direction orthogonal to the third rotation axis acting on the shaft by a rotational operation of the first arm or the second arm based on a detection value of the detection unit, A second acquisition unit that acquires a bending stress F1 applied to a predetermined portion of the shaft based on the force F acquired by the first acquisition unit, A comparison unit that compares a maximum bending stress F0 that the predetermined portion of the shaft can withstand with the bending stress F1 acquired by the second acquisition unit, A robot system, characterized in that it has a notification signal generation unit that generates a notification signal for notifying an overload state of the shaft when a comparison result by the comparison unit is F1≧F0.

8. A program for detecting an overload state of the shaft in a robot having a base, a first arm rotatably connected to the base about a first rotation axis, a second arm rotatably connected to the first arm about a second rotation axis parallel to the first rotation axis, a shaft rotatably connected to the second arm about a third rotation axis parallel to the first rotation axis and movable along the third rotation axis, the program comprising: A first step of acquiring a force F in a direction orthogonal to the third rotation axis acting on the shaft by a rotational operation of the first arm or the second arm, A second step of acquiring a bending stress F1 applied to a predetermined portion of the shaft based on the force F acquired in the first step, A third step of comparing a maximum bending stress F0 that the predetermined portion of the shaft can withstand with the bending stress F1 acquired in the second step, A fourth step of notifying an overload state of the shaft when a comparison result in the third step is F1≧F0, for executing the program.

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