Control method for robot system

Abstract

To provide a control method of a robot system capable of accurately predicting a temperature when a power supply of a robot is turned on.SOLUTION: A control method for a robot system includes a temperature storing step of storing an OFF-time temperature, which is a temperature of a robot arm at a first timing when a power supply of a robot is switched from ON to OFF, an elapsed time acquiring step of acquiring an elapsed time from the first timing to a second timing when the power supply is turned on next, and a temperature predicting step of predicting an ON-time temperature, which is a temperature of the robot arm at the second timing, based on the OFF-time temperature and the elapsed time.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a robot system. [Background technology]

[0002] Patent Document 1 discloses a configuration for calculating the temperature at a predetermined position of a robot based on the temperature measured by a temperature sensor in an encoder built into a motor for moving a robot arm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-297829 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the configuration of Patent Document 1 does not take into consideration the calculation of the temperature at the predetermined position when the robot is turned on again after a certain time has passed since it was turned off, which may result in an inappropriate calculation of the temperature of the robot when it is turned on. [Means for solving the problem]

[0005] The control method for a robot system of the present invention includes a temperature storage step of storing an OFF temperature, which is the temperature of the robot arm at a first timing when the power supply of the robot is switched from ON to OFF; an elapsed time acquisition step of acquiring an elapsed time from the first timing to a second timing at which the power is next turned on; and a temperature prediction step of predicting an ON temperature, which is the temperature of the robot arm at the second timing, based on the OFF temperature and the elapsed time.

[0006] The control method for a robot system of the present invention includes a temperature storage step of storing an OFF temperature, which is the temperature of the robot arm at a first timing when the power supply of the robot is switched from ON to OFF; an elapsed time acquisition step of acquiring an elapsed time from the first timing to a second timing at which the power is next turned on; If the elapsed time is less than a second threshold, an ON temperature, which is the temperature of the robot arm at the second timing, is predicted based on the OFF temperature and the elapsed time, and if the elapsed time is equal to or greater than the second threshold, a temperature prediction step is performed to set a reference temperature as the ON temperature. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an overall view of a robot system according to a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating an example of DH parameters. [Figure 3] 10 is a flowchart illustrating a control method for the robot system. [Figure 4] FIG. 10 is a diagram for explaining a method for predicting an ON-state temperature. [Figure 5] FIG. 10 is a diagram for explaining a method for predicting an ON-state temperature. [Figure 6] 10 is a graph showing an example of changes in temperature of a robot arm over time. [Figure 7] 10 is a flowchart showing a control method for a robot system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for controlling a robot system according to the present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0009] First Embodiment FIG. 1 is an overall view of a robot system according to a first embodiment. FIG. 2 is a diagram showing an example of DH parameters. FIG. 3 is a flowchart showing a control method for the robot system. FIGS. 4 and 5 are diagrams for explaining a method for predicting ON-state temperature. FIG. 6 is a graph showing an example of changes in the temperature of a robot arm over time.

[0010] As shown in FIG. 1, the robot system 1 includes a robot 2 and a robot control device 3 that controls the driving of the robot 2.

[0011] Robot 2 As shown in FIG. 1, the robot 2 is a six-axis vertical articulated robot having six drive axes, and has a base 21 fixed to a mounting table, floor, etc., a robot arm 22 rotatably connected to the base 21, and an end effector 23 attached to the tip of the robot arm 22.

[0012] The robot arm 22 has six arms 221, 222, 223, 224, 225, and 226 rotatably connected in this order from the base 21 side, and includes six joints J1, J2, J3, J4, J5, and J6. Specifically, the arm 221 is rotatably connected to the base 21 via the joint J1, the arm 222 is rotatably connected to the arm 221 via the joint J2, the arm 223 is rotatably connected to the arm 222 via the joint J3, the arm 224 is rotatably connected to the arm 223 via the joint J4, the arm 225 is rotatably connected to the arm 224 via the joint J5, and the arm 226 is rotatably connected to the arm 226 via the joint J6.

[0013] Among the joints J1 to J6, joints J2, J3, and J5 are bending joints, and joints J1, J4, and J6 are torsion joints. Each of the joints J1, J2, J3, J4, J5, and J6 is equipped with a drive mechanism including, for example, a three-phase AC motor, a reducer T that reduces the rotational speed of the motor M, increases the torque, and outputs the torque. The robot control device 3 independently drives the motors M of the joints J1, J2, J3, J4, J5, and J6 based on operation commands received from a host computer (not shown), thereby moving a tool center point (TCP) at the tip of the robot arm 22 to a desired position at a desired posture and speed. However, the configuration of the drive mechanism is not particularly limited as long as it can drive each of the joints J1 to J6.

[0014] The end effector 23 is attached to the tip of the robot arm 22, that is, to the arm 226. There are no particular limitations on the end effector 23, and an end effector appropriate for the task that the robot 2 is to perform is attached.

[0015] The robot 2 also has a temperature sensor 29 disposed inside the robot arm 22 as a temperature detection unit that detects the temperature of the robot arm 22. In the illustrated example, the temperature sensor 29 is disposed inside the arm 221, but the location and number of the temperature sensors 29 are not particularly limited. For example, one temperature sensor 29 may be disposed on each of the arms 221 to 226. Alternatively, the temperature sensor 29 may be disposed on the outside of the robot arm 22. Encoders equipped with a temperature sensor for correcting their own output value are known, and if such an encoder is used as the encoder E, the temperature sensor provided in the encoder E may be used as the temperature sensor 29.

[0016] The robot 2 has been described above, but there are no particular limitations on the robot 2. For example, it may be a horizontal articulated robot (SCARA robot) or a dual-arm robot equipped with two robot arms 22.

[0017] <Robot control device 3> As shown in FIG. 1, the robot control device 3 has a temperature storage unit 31, an elapsed time acquisition unit 32, and a temperature prediction unit 33. Of these, the temperature storage unit 31 stores an OFF-time temperature Temp1, which is the temperature of the robot arm 22 at a first timing T1 when the power of the robot 2 is switched from ON to OFF. The elapsed time acquisition unit 32 acquires an elapsed time D from the first timing T1 to a second timing T2 when the power of the robot 2 is next turned ON. The temperature prediction unit 33 predicts an ON-time temperature Temp2, which is the temperature of the robot arm 22 at the second timing T2, based on the OFF-time temperature Temp1 and the elapsed time D. The robot control device 3 configured in this way can appropriately predict and calculate the temperature of the robot arm 22 at the second timing T2.

[0018] Such a robot control device 3 is, for example, composed of a computer, and is a controller having a processor (CPU) that processes information, a memory communicatively connected to the processor, and an external interface that connects to the robot 2 and a host computer. Various programs that can be executed by the processor are stored in the memory, and the processor reads and executes the programs stored in the memory, thereby realizing the temperature memory unit 31, elapsed time acquisition unit 32, and temperature prediction unit 33 described above.

[0019] The robot control device 3 stores in its memory, for example, DH parameters P as shown in Fig. 2. The DH parameters P contain the lengths d1, a2, Lx3, a4, d4, and d7 of each part of the robot arm 22. Therefore, the robot control device 3 can detect the position and orientation of the tip of the robot arm 22, i.e., the TCP, based on the amount of rotation of each motor M detected by each encoder E and the DH parameters P.

[0020] However, for example, heat from a heat source such as the motor M can cause the robot arm 22 to thermally expand, resulting in a discrepancy between the length of each part of the robot arm 22 set in the DH parameter P and the actual length. In this case, the position and orientation of the TCP of the robot arm 22 detected by the robot control device 3 (hereinafter also referred to as the "detected value") deviates from the actual position and orientation of the TCP (hereinafter also referred to as the "actual value"). Therefore, the robot control device 3 predicts the temperature of the robot arm 22 and corrects the DH parameter P (the length of each part of the robot arm 22) based on the prediction result, thereby suppressing the discrepancy between the detected value and the actual value of the TCP. This enables the robot arm 22 to be controlled with high precision. The above control method will be described in detail below with reference to the flowchart shown in FIG. 3.

[0021] As shown in Figure 3, the control method of the robot system 1 includes a temperature storage step S1 for storing the OFF temperature Temp1, which is the temperature of the robot arm 22 at a first timing T1 when the power of the robot 2 is switched from ON to OFF; an elapsed time acquisition step S2 for acquiring the elapsed time D from the first timing T1 to a second timing T2 when the power of the robot 2 is next turned ON; a temperature prediction step S3 for predicting the ON temperature Temp2, which is the temperature of the robot arm 22 at the second timing T2, based on the OFF temperature Temp1 and the elapsed time D; a correction step S4 for correcting the DH parameter P based on the ON temperature Temp2; and a drive step S5 for controlling the drive of the robot 2 using the corrected DH parameter P.

[0022] <Temperature storage step S1> In the temperature storage step S1, first, the robot control device 3 determines whether the power supply of the robot 2 has been switched from ON to OFF. For example, the power supply of the robot 2 being ON refers to a state in which power is supplied to the robot control device 3 and calculation processing can be performed using the CPU, and the power supply being OFF refers to a state in which power is not supplied to the robot control device 3 and calculation processing cannot be performed using the CPU. However, the definition of power supply ON / OFF is not limited to this. For example, the power supply of the robot 2 being ON may refer to a state in which power (drive signals) is supplied to each motor M, and the power supply of the robot 2 being OFF may refer to a state in which power is not supplied to each motor M.

[0023] When the power supply of the robot 2 is switched from ON to OFF, the robot control device 3 stores the temperature of the robot arm 22 at a first timing T1, which is the timing when the power supply is switched from ON to OFF, as the OFF-state temperature Temp1. In particular, in this embodiment, the OFF-state temperature Temp1 of each of the arms 221 to 226 included in the robot arm 22 is stored. In other words, the OFF-state temperature Temp1 includes the OFF-state temperature of the arm 221, the OFF-state temperature of the arm 222, the OFF-state temperature of the arm 223, the OFF-state temperature of the arm 224, the OFF-state temperature of the arm 225, and the OFF-state temperature of the arm 226.

[0024] The OFF-state temperature Temp1 can be calculated, for example, using a thermal network method based on the temperature detected by the temperature sensor 29 at the time immediately preceding the first timing T1. Examples of heat values ​​used in the thermal network method include copper loss, iron loss, and mechanical loss due to each motor M, and transmission efficiency and mechanical loss due to each reducer T. Examples of heat dissipation include natural convection, forced convection, and radiation. However, the method for calculating the OFF-state temperature Temp1 is not particularly limited. For example, if a temperature sensor 29 is provided for each arm 221-226, the temperature detected by each temperature sensor 29 may be used as the OFF-state temperature of the arm to which the temperature sensor 29 is provided. The robot control device 3 then stores the time of the first timing T1 and the OFF-state temperature Temp1 calculated as described above.

[0025] <Elapsed time acquisition step S2> In the elapsed time acquisition step S2, first, the robot control device 3 determines whether the power of the robot 2 has been switched from OFF to ON. If the power of the robot 2 has been switched from OFF to ON, then the robot control device 3 acquires the time difference between the first timing T1 and the second timing T2, which is the timing when the power of the robot 2 was switched ON, i.e., the elapsed time D from the first timing T1 to the second timing T2. Then, the robot control device 3 stores the elapsed time D.

[0026] <Temperature prediction step S3> In the temperature prediction step S3, the robot control device 3 first compares the elapsed time D acquired in the elapsed time acquisition step S2 with a preset first threshold value TH1. Note that the first threshold value TH1 is not particularly limited and varies depending on the configuration of the robot 2, but in this embodiment it is set to one hour.

[0027] If the elapsed time D is less than the first threshold value TH1, the robot control device 3 divides the period from the first timing T1 to the second timing T2 into N sections Q, where N is equal to or greater than 2. On the other hand, if the elapsed time D is equal to or greater than the first threshold value TH1, the robot control device 3 compares the elapsed time D with a preset second threshold value TH2, where the second threshold value TH2 is greater than the first threshold value TH1. The second threshold value TH2 is not particularly limited and varies depending on the configuration of the robot 2, but in this embodiment it is set to 12 hours. If the elapsed time D is less than the second threshold value TH2, the robot control device 3 divides the period from the first timing T1 to the second timing T2 into M sections Q, where M is equal to or greater than 2, and in this embodiment in particular, M is equal to or greater than N.

[0028] The robot control device 3 then repeats temperature prediction of the robot arm 22 for each interval Q determined in the previous step, and finally predicts the ON-time temperature Temp2. ​​That is, if the elapsed time D<first threshold TH1, the robot control device 3 repeats temperature prediction of the robot arm 22 for each N intervals Q, and finally predicts the ON-time temperature Temp2. ​​If the elapsed time D≧first threshold TH1 and the elapsed time D<second threshold TH2, the robot control device 3 repeats temperature prediction of the robot arm 22 for each N intervals Q, and finally predicts the ON-time temperature Temp2. ​​Note that the method for predicting the ON-time temperature Temp2 is the same regardless of the number of intervals Q. Therefore, for convenience of explanation, the following will representatively describe an example in which the period from the first timing T1 to the second timing T2 is divided into four intervals Q1, Q2, Q3, and Q4 as shown in FIG. 4.

[0029] First, the robot control device 3 predicts the temperature TempA of the robot arm 22 at the interval end timing Tb of interval Q1 using the thermal network method based on the time length of interval Q1 and the temperature (= OFF temperature Temp1) of the robot arm 22 at the interval start timing Ta (= first timing T1) of interval Q1. Next, the robot control device 3 predicts the temperature TempB of the robot arm 22 at the interval end timing Td of interval Q2 using the thermal network method based on the time length of interval Q2 and the temperature TempA of the robot arm 22 at the interval start timing Tc (= interval end timing Tb) of interval Q2. Next, the robot control device 3 predicts the temperature TempC of the robot arm 22 at the interval end timing Tf of interval Q2 using the thermal network method based on the time length of interval Q3 and the temperature TempB of the robot arm 22 at the interval start timing Te (= interval end timing Td) of interval Q3. Next, the robot control device 3 predicts the temperature TempD of the robot arm 22 at the interval end timing Th (= second timing T2) of interval Q4 using a thermal network method based on the time length of interval Q4 and TempC, which is the temperature of the robot arm 22 at the interval start timing Tg (= interval end timing Tf) of interval Q4. The robot control device 3 then sets the temperature TempD to the ON-time temperature Temp2. ​​In this way, by dividing the period from the first timing T1 to the second timing T2 into multiple intervals Q and repeatedly predicting the temperature of the robot arm 22 for each interval Q, the prediction accuracy of the ON-time temperature Temp2 is improved compared to, for example, when the period is not divided into multiple intervals Q. As a result, the robot control device 3 can predict the ON-time temperature Temp2 more accurately.

[0030] In particular, as in this embodiment, when the elapsed time D<the first threshold value TH1, the elapsed time is divided into N intervals Q, and when the elapsed time D≧the first threshold value TH1, the elapsed time is divided into M (M>N) intervals Q, so that the period from the first timing T1 to the second timing T2 can be divided into an appropriate number of intervals Q according to the length of the elapsed time D. This allows the robot control device 3 to more accurately predict the ON temperature Temp2.

[0031] In FIG. 4, each interval Q has the same time length. Setting each interval Q to the same time length facilitates the setting of the intervals Q. However, this is not limited thereto. For example, as shown in FIG. 5, the time length of the intervals Q may gradually increase in chronological order from the first interval Q1 to the last interval Q4. As shown in FIG. 6, when the robot 2 is powered off, the temperature of the robot arm 22 begins to drop sharply, then the rate of decrease gradually decreases, and finally converges to the outside air temperature. In other words, the rate of temperature decrease per unit time gradually decreases as time passes from the time of power off. Therefore, by gradually increasing the time length from the first interval Q1 to the last interval Q4 in accordance with this, the temperature difference of the robot arm 22 between the interval start timing and the interval end timing in each interval Q can be kept small, thereby further improving the accuracy of the temperature prediction. As a result, the robot control device 3 can predict the ON temperature Temp2 more accurately.

[0032] The time length of the interval Q can be determined, for example, as follows. For example, when the number of intervals Q is four, the time length can be determined based on n={Log10(elapsed time D)-Log10(lower limit of calculation time required for temperature prediction)} / number of intervals Q... (1) and dt=10^{Log10(lower limit of calculation time required for temperature prediction)+n)-10^{Log10(lower limit of calculation time required for temperature prediction)+n-1) (n=1→4)... (2). However, the method for determining the time length of the interval Q is not particularly limited.

[0033] Now, let us return to the step of comparing the elapsed time D with the second threshold TH2. As described above, if the elapsed time D is less than the second threshold TH2, the robot control device 3 divides the period from the first timing T1 to the second timing T2 into M sections Q. On the other hand, if the elapsed time D is greater than or equal to the second threshold TH2, the robot control device 3 sets the reference temperature to the ON temperature Temp2. ​​The reference temperature is the temperature of the robot arm 22 at the second timing acquired from a different means than the OFF temperature Temp1. In this embodiment, the reference temperature is the ambient temperature of the robot 2 detected by the temperature sensor 4 disposed in the space in which the robot 2 is placed, i.e., the outside air temperature around the robot 2. As described above, when the robot 2 is powered off, the temperature of the robot arm 22 decreases over time and eventually converges to the outside air temperature. Therefore, if the elapsed time D is sufficiently long, such as if the elapsed time D is greater than or equal to the second threshold TH2, it can be estimated that the temperature of the robot arm 22 is equal to the outside air temperature. Therefore, when the elapsed time D is equal to or greater than the second threshold value TH2, it can be estimated that the ON temperature Temp2 is equal to the outside air temperature, and the ON temperature Temp2 can be predicted easily and accurately without performing complex calculations using the thermal network method as described above. However, the reference temperature is not limited to the outside air temperature detected by the temperature sensor 4. For example, as described above, if the encoder E has a built-in temperature sensor, the temperature detected by the temperature sensor included in the encoder E may be used as the reference temperature.

[0034] This completes the prediction of ON temperature Temp2 when elapsed time D<first threshold TH1, when elapsed time D≧first threshold TH1 and elapsed time D<second threshold TH2, and when elapsed time D≧second threshold TH2.

[0035] <Correction Step S4> In the correction step S4, the robot controller 3 corrects the DH parameter P based on the predicted ON-time temperature Temp2.

[0036] <Driving step S5> In the driving step S4, the robot control device 3 controls the driving of the robot 2 using the corrected DH parameter P.

[0037] According to this method, the ON-time temperature Temp2 can be predicted with high accuracy. Therefore, the driving step S5 can be performed with high accuracy. Also, the highly accurate driving of the robot arm 22 can be started immediately after the power of the robot 2 is turned on. Therefore, the work efficiency and work accuracy of the robot system 1 are improved.

[0038] The control method for the robot system 1 has been described above. As described above, the control method for the robot system 1 includes a temperature storage step S1 for storing the OFF-state temperature Temp1, which is the temperature of the robot arm 22 at a first timing T1 when the power supply to the robot 2 is switched from ON to OFF; an elapsed time acquisition step S2 for acquiring the elapsed time D from the first timing T1 to a second timing T2 when the power supply to the robot 2 is next turned ON; and a temperature prediction step S3 for predicting the ON-state temperature Temp2, which is the temperature of the robot arm 22 at the second timing T2, based on the OFF-state temperature Temp1 and the elapsed time D. This method allows the ON-state temperature Temp2 to be predicted with high accuracy. Therefore, the driving step S5 can be performed with high accuracy. Furthermore, the robot arm 22 can be driven with high accuracy immediately after the power supply to the robot 2 is turned ON. This improves the work efficiency and work accuracy of the robot system 1.

[0039] As described above, in the temperature prediction step S3, the period from the first timing T1 to the second timing T2 is divided into a plurality of intervals Q1 to Q4, and for each of the intervals Q1 to Q4, the temperature of the robot arm 22 at the interval end timing is predicted based on the temperature of the robot arm 22 at the interval start timing and the interval time length, by repeating this process in chronological order from the first interval Q1 to the last interval Q4, thereby predicting the ON-time temperature Temp2. ​​According to this method, the ON-time temperature Temp2 can be predicted with higher accuracy.

[0040] As described above, the number of sections Q is set to be different when the elapsed time D is less than the first threshold value TH1 and when it is equal to or greater than the first threshold value TH1. This allows the ON-state temperature Temp2 to be predicted with higher accuracy regardless of the length of the elapsed time D.

[0041] As described above, the interval time length may be gradually increased in chronological order from the first interval Q1 to the last interval Q4. This method minimizes the temperature difference of the robot arm 22 between the start and end of each interval Q, further improving the accuracy of the temperature prediction. This allows the robot control device 3 to more accurately predict the ON-state temperature Temp2.

[0042] As described above, the control method for the robot system 1 includes a temperature storage step S1 for storing an OFF-time temperature Temp1, which is the temperature of the robot arm 22 at a first time T1 when the power supply to the robot 2 is switched from ON to OFF, and an elapsed time acquisition step S2 for acquiring an elapsed time D from the first time T1 to a second time T2 when the power supply to the robot 2 is next turned ON. If the elapsed time D is less than a second threshold TH2, an ON-time temperature Temp2, which is the temperature of the robot arm 22 at the second time T2, is predicted based on the OFF-time temperature Temp1 and the elapsed time D. If the elapsed time D is equal to or greater than the second threshold TH2, a temperature prediction step S3 for setting the ON-time temperature Temp2 as the reference temperature is also included. This method allows for accurate prediction of the ON-time temperature Temp2. ​​Furthermore, it is easy to predict the ON-time temperature Temp2 when the elapsed time D is equal to or greater than the second threshold TH2. Therefore, the robot arm 22 can be driven with high precision immediately after the power supply to the robot 2 is turned ON. This improves the work efficiency and work accuracy of the robot system 1.

[0043] Second Embodiment FIG. 7 is a flowchart showing a control method for a robot system according to the second embodiment.

[0044] The control method for the robot system according to this embodiment is the same as that of the first embodiment, except for the temperature prediction step S3. Therefore, in the following description, the control method for the robot system according to this embodiment will be described focusing on the differences from the first embodiment, and a description of the similarities will be omitted. In addition, in each drawing of this embodiment, the same reference numerals are used to designate the same components as those in the above-described embodiment.

[0045] 5, in the control method for a robot system of this embodiment, the period from the first timing T1 to the second timing T2 is divided into N intervals Q, regardless of the length of the elapsed time D. In other words, the number of intervals Q is constant regardless of the elapsed time D. According to this method, the amount of processing in the temperature prediction step S3 is reduced compared to the first embodiment described above, and the ON-state temperature Temp2 can be predicted more easily.

[0046] The second embodiment can also achieve the same effects as the first embodiment described above.

[0047] Although the control method for the robot system of the present invention has been described above with reference to the illustrated embodiment, the present invention is not limited to this, and the configurations and steps of each part can be replaced with any configurations and steps having similar functions. Furthermore, any other configurations and steps may be added to the present invention. Furthermore, each embodiment may be combined as appropriate. [Explanation of symbols]

[0048] 1...Robot system, 2...Robot, 21...Base, 22...Robot arm, 221...Arm, 222...Arm, 223...Arm, 224...Arm, 225...Arm, 226...Arm, 23...End effector, 29...Temperature sensor, 3...Robot control device, 301...Processor, 302...Memory, 303...External interface, 31...Temperature storage unit, 32...Elapsed time acquisition unit, 33...Temperature prediction unit, 4...Temperature sensor, D...Elapsed time, E...Encoder, J1...Joint, J2...Joint, J3...Joint, J4...Joint, J5...Joint, J6...Joint, M...Motor, P...DH parameter, Q...Section, Q1... Interval, Q2...interval, Q3...interval, Q4...interval, S1...temperature storage step, S2...elapsed time acquisition step, S3...temperature prediction step, T...reduction gear, T1...first timing, T2...second timing, TH1...first threshold, TH2...second threshold, Ta...interval start timing, Tb...interval end timing, Tc...interval start timing, Td...interval end timing, Te...interval start timing, Tf...interval end timing, Tg...interval start timing, Th...interval end timing, Temp1...temperature when OFF, Temp2...temperature when ON, TempA...temperature, TempB...temperature, TempC...temperature, TempD...temperature

Claims

1. a temperature storage step of storing an OFF temperature, which is the temperature of the robot arm at a first timing when the power of the robot is switched from ON to OFF; an elapsed time acquisition step of acquiring an elapsed time from the first timing to a second timing at which the power is next turned on; a temperature prediction step of predicting an ON temperature, which is the temperature of the robot arm at the second timing, based on the OFF temperature and the elapsed time.

2. 2. A control method for a robot system according to claim 1, wherein the temperature prediction step divides the period from the first timing to the second timing into a plurality of intervals, and for each interval, predicts the temperature of the robot arm at the interval end timing based on the temperature of the robot arm at the interval start timing and the interval time length by repeating this process in chronological order from the first interval to the last interval.

3. The method for controlling a robot system according to claim 2 , wherein the number of sections is constant regardless of the elapsed time.

4. The method for controlling a robot system according to claim 2 , wherein the number of sections is made different when the elapsed time is less than a first threshold value and when the elapsed time is equal to or greater than the first threshold value.

5. 5. The method for controlling a robot system according to claim 3, wherein the section time lengths gradually increase in chronological order from the first section to the last section.

6. a temperature storage step of storing an OFF temperature, which is the temperature of the robot arm at a first timing when the power of the robot is switched from ON to OFF; an elapsed time acquisition step of acquiring an elapsed time from the first timing to a second timing at which the power is next turned on; a temperature prediction step of predicting an ON temperature, which is the temperature of the robot arm at the second timing, based on the OFF temperature and the elapsed time if the elapsed time is less than a second threshold value, and setting a reference temperature as the ON temperature if the elapsed time is equal to or greater than the second threshold value.

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