Control Method For Control Device Controlling Robot Arm, Non-Transitory Computer-Readable Storage Medium Storing Computer Program, And Control Device

A method according to the present disclosure includes: (a) carrying out overexcitation of an electromagnetic brake; (b) controlling a fan cooling a control device in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

The present application is based on, and claims priority from JP Application Serial Number 2021-204004, filed Dec. 16, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a control method for a control device controlling a robot arm, a non-transitory computer-readable storage medium storing a computer program, and a control device.

2. Related Art

JP-A-2006-280076 discloses a control device having a drive circuit that drives a motor of a robot, and a fan that cools the drive circuit. This control device is configured in such a way that a fan motor is driven using electrical energy stored in a smoothing capacitor, thus cooling the inside of the control device.

As a motor of a robot arm, a motor having an overexcitation-type electromagnetic brake is known. When starting to electrify such a motor, an overexcitation current is applied to the electromagnetic brake to release the brake and therefore the power consumption of the control device temporarily increases. However, the related art has a problem in that sufficient measures are not taken to restrain the increase in the power consumption of the control device due to the overexcitation of the electromagnetic brake and to efficiently cool the control device.

SUMMARY

According to a first aspect of the present disclosure, a control method for a control device controlling a robot arm having a motor braked by an overexcitation-type electromagnetic brake is provided. The control method includes: (a) carrying out overexcitation of the electromagnetic brake; (b) controlling a fan cooling the control device in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

According to a second aspect of the present disclosure, a non-transitory computer-readable storage medium storing a computer program for control of a control device controlling a robot arm having a motor braked by an overexcitation-type electromagnetic brake is provided. The computer program causes a processor to execute: (a) processing of carrying out overexcitation control of the electromagnetic brake; (b) processing of controlling a fan cooling the control device in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) processing of controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

According to a third aspect of the present disclosure, a control device controlling a robot arm having a motor braked by an overexcitation-type electromagnetic brake is provided. The control device includes: a motor diver circuit supplying electric power to the motor; a control power supply supplying electric power to the electromagnetic brake; a fan operating when receiving supply of electric power from the control power supply and thus cooling the control device; and a control unit controlling the motor driver circuit and the fan. The control unit executes: (a) processing of carrying out overexcitation of the electromagnetic brake; (b) processing of controlling the fan in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) processing of controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG.1is an explanatory view showing an example of a robot system according to an embodiment. The robot system has a robot100, a control device200controlling the robot100, and an information processing device300. The information processing device300is, for example, a personal computer. A user can input an instruction to cause the robot100to operate, using the information processing device300. This instruction is supplied from the information processing device300to the control device200. In response to the instruction, the control device200controls the operation of the robot100. The control device200may also accept an instruction from another external device than the information processing device300.

The robot100has a base110and a robot arm120. An end effector150is installed at an arm end122, which is a distal end part of the robot arm120. The robot arm120is formed of parts sequentially coupled via six joints J1to J6. Of these joints J1to J6, three joints J2, J3, J5are bending joints and the other three joints J1, J4, J6are torsional joints. While a six-axis robot is described as an example in this embodiment, a robot having any robot arm mechanism having one or more joints can be used. Also, while the robot100in this embodiment is a vertical articulated robot, a horizontal articulated robot may be used.

FIG.2is a block diagram showing the internal configuration of the control device200. InFIG.2, a communication line is drawn as a dotted line and a power line is drawn as a solid line. The plurality of joints J1to J6of the robot arm120are provided with motors M1to M6and overexcitation-type electromagnetic brakes B1to B6, respectively. The overexcitation type is a system in which, when the power is turned on, a large overexcitation current is applied to switch the electromagnetic brake from a brake active state to a brake release state, and in which subsequently the brake release state is maintained with a hold current smaller than the overexcitation current. When the electrification of the electromagnetic brake is stopped, the electromagnetic brake turns into the brake active state.

The control device200has a casing210, a motor driver unit220, a control power supply230, a control unit240controlling the other components in the control device200, a cooling fan250blowing air to the motor driver unit220, and a ventilation fan260exchanging the air inside and outside the casing210. The motor driver unit220provides a current to the motors M1to M6of the robot arm120and thus drives the motors M1to M6. The motor driver unit220has, for example, motor driver circuits221to226provided corresponding to the motors M1to M6, respectively. The motor driver circuits221to226each have a plurality of switching elements such as a transistor and a MOSFET, and switch on and off the switching elements to control the current flowing to the motors M1to M6and thus drive the motors M1to M6. The control power supply230supplies electric power to the control unit240, the cooling fan250, and the ventilation fan260, and also supplies electric power to the electromagnetic brakes B1to B6of the robot arm120.

The casing210is substantially in the shape of a rectangular parallelepiped and accommodates the other components. The motor driver unit220has a power semiconductor such as an IPM (intelligent power module) and is therefore a large heat source. The cooling fan250blows air to the motor driver unit220and thus cools the motor driver unit220. The cooling fan250also has a function as a circulator circulating the air inside the casing210. The ventilation fan260is attached to a wall of the casing210and exchanges the air inside and outside the casing210and thus cools the entirety of the control device200. In the example shown inFIG.2, two ventilation fans260are provided. However, three or more ventilation fans260may be provided. Alternatively, only one ventilation fan260may be provided. Both of the cooling fan250and the ventilation fan260function as a fan for cooling the control device200and particularly function as a fan for cooling the motor driver unit220. Also, one of the cooling fan250and the ventilation fan260may be omitted.

The electric power for the motors M1to M6of the robot arm120is supplied from the motor driver unit220via a first power line PL1. The electric power for the electromagnetic brakes B1to B6is supplied from the control power supply230via a second power line PL2. The second power line PL2is coupled to the electromagnetic brakes B1to B6, for example, in a daisy chain. Coupling via a bus may be used instead of a daisy chain. In any case, it is preferable that the plurality of electromagnetic brakes B1to B6are coupled via the second power line PL2, which is a common power supply line.

The electromagnetic brakes B1to B6are also coupled to the control unit240via a communication line CL. The control unit240transmits an operation command to the electromagnetic brakes B1to B6via the communication line CL. Each of the electromagnetic brakes B1to B6may have a brake unit BM executing the braking on the joint and a brake driver circuit BD driving the brake unit BM. The brake driver circuit BD controls the operation of the brake unit BM in response to the operation command given from the control unit240. Also, the brake driver circuit BD may be omitted and the control unit240may directly control the brake unit BM.

The control unit240has a processor241and a memory242. The control unit240executes a computer program stored in the memory and thus controls the other components in the control device200. This computer program may be stored in a non-transitory recording medium such as a hard disk or an optical disk. The functions of the control unit240may also be implemented by a hardware circuit.

FIG.3is a timing chart showing a control operation in the embodiment. This control operation is executed by the control unit240.FIG.3shows changes as described below. WhileFIG.3shows a temperature Td of one of the motor driver circuits221to226as an example, the temperature Td of any one of these motor driver circuits is expressed in a similar graph.

(1) The excitation/non-excitation state of the motors M1to M6

(2) The OFF/overexcitation/hold excitation state of the electromagnetic brakes B1to B6

(3) The ON/OFF state of the cooling fan250

(4) The ON/OFF state of the ventilation fan260

(5) The temperature Td of the motor driver circuits221to226

(6) The power consumption Wc of the control power supply230

The horizontal axis inFIG.3represents time and is divided into five periods as described below. The states of the electromagnetic brakes B1to B6, the cooling fan250, and the ventilation fan260in each period are as described below.

A period P1is a period when the motors M1to M6are in the non-excitation state, that is, not supplied with electric power.

The electromagnetic brakes B1to B6are in a non-electrified braking state, that is, the brake active state.

The cooling fan250is in the OFF state.

The ventilation fan260is in the ON state.

The aim of setting the ventilation fan260in the ON state is to prevent the control unit240from being heated. Even in this period P1, the control unit240monitors the state of the robot100and is on standby for accepting an input from outside. In the period P1, the amount of heat generated in the control device200is smaller than in a period P3when the robot arm120is in operation. Therefore, it is preferable to reduce the cooling ability of the ventilation fan260than in the period P3and thus reduce the power consumption. Specifically, at least one of the plurality of ventilation fans260may be on. Alternatively, all the ventilation fans260may be on but the number of rotations thereof may be less than in the period P3.

A period P2is a period immediately after the excitation of the motors M1to M6is started. The period P2is an overexcitation period when the overexcitation of the electromagnetic brakes B1to B6is carried out. The length of this period P2is, for example, approximately 0.4 seconds to approximately 1.2 seconds.

The electromagnetic brakes B1to B6enter a non-braking state with hold excitation, that is, the brake release state, after the braking is cancelled by overexcitation.

The cooling fan250is maintained in the OFF state.

The ventilation fan260is switched to the OFF state.

The aim of setting the cooling fan250and the ventilation fan260in the OFF state is to prevent an excessive increase in the power consumption of the control power supply230in the overexcitation, because a large overexcitation current is generated by the overexcitation of the electromagnetic brakes B1to B6. In the period P2, the cooling fan250and all the ventilation fans260may be in the OFF state. However, instead of this, the power consumption of these fans may be made lower than in the period P3. For example, the cooling fan250and only a part of the ventilation fans260may be in the ON state, or the number of rotations thereof may be reduced. The power consumption of the cooling fan250and the ventilation fan260in the period P2is referred to as “first power consumption”. The first power consumption is preferably zero but may be a non-zero value.

As the control unit240accepts an instruction to cause the robot arm120to operate from the information processing device300at a start timing t1of the period P2, the control unit240, in response to this instruction, transmits a command to excite the motors M1to M6to the motor driver circuits221to226and also transmits a command to overexcite the electromagnetic brakes B1to B6in the braking state. In the example shown inFIG.3, the timings of overexciting the electromagnetic brakes B1to B6are shifted from each other. Thus, the power consumption due to the overexcitation can be made uniform and therefore the power peak can be restrained.

The period P3is a period when the electromagnetic brakes B1to B6are in the brake release state, the motors M1to M6are excited, and the robot arm120is operable.

All of the electromagnetic brakes B1to B6are in the brake release state.

The cooling fan250is switched to the ON state.

All of the ventilation fans260are switched to the ON state.

As the method for generating a command to start driving the cooling fan250and the ventilation fan260at a start timing t2of the period P3, for example, the following two methods are conceivable. In the first method, the control unit240measures time from the start timing t1of the period P2, with a timer, and generates a drive command for the cooling fan250and the ventilation fan260after the lapse of a predetermined time. In the second method, the control unit240generates a drive command for the cooling fan250and the ventilation fan260substantially at the same time as transmitting a command to stop the overexcitation of the electromagnetic brake B1, which is the last one to be overexcited.

The power consumption of the cooling fan250and the ventilation fan260in the period P3is referred to as “second power consumption”. The second power consumption is higher than the first power consumption, which is the power consumption of the cooling fan250and the ventilation fan260in the period P2.

A period P4is a period immediately after the motors M1to M6are switched to the non-excitation state at a timing t3. The length of the period P4is, for example, approximately one minute to approximately five minutes.

All of the electromagnetic brakes B1to B6are switched to the non-excitation brake active state.

The cooling fan250is maintained in the ON state.

All of the ventilation fans260are maintained in the ON state.

The reason for maintaining the cooling fan250and the ventilation fans260in the ON state is that the temperature Td of the motor driver circuits221to226is high immediately after the motors M1to M6are switched to the non-excitation state.

A period P5is a period when the motors M1to M6are in the non-excitation state, that is, the state of not being supplied with electric power. The state in the period P5is the same as in the period P1.

The electromagnetic brakes B1to B6are in the non-electrified braking state, that is, the brake active state.

The cooling fan250is in the OFF state.

The ventilation fan260is in the ON state.

A start timing t4of the period P5is a time point when the temperature Td of the motor driver circuits221to226has sufficiently dropped. This timing t4may be decided by the control unit240measuring the temperature Td of the motor driver circuits221to226, using a temperature sensor, or may be decided by the control unit240measuring time from the start timing t3of the period P4, with the timer. At the beginning of the period P5, the temperature Td of the motor driver circuits221to226rises slightly due to the switching of the cooling fan250to the OFF state. However, the scale of the rise is sufficiently small and does not pose any problem.

The temperature Td of the motor driver circuits221to226reaches a maximum value in the period P3. However, the cooling by the cooling fan250and the ventilation fan260is executed so that the temperature Td does not become excessively high. The power consumption Wc of the control power supply230reaches a maximum value Wc_max1in the period P3. In the overexcitation period P2, the power consumption Wc is restrained to a smaller value than in the period P3. This point will be described further in detail later.

FIG.4is an explanatory view showing a change in the state of the plurality of electromagnetic brakes in the period P2shown inFIG.3. As described with reference toFIG.3, in this embodiment, the timings of overexciting the electromagnetic brakes B1to B6are shifted from each other. More specifically, individual overexcitation periods PP during which the individual electromagnetic brakes are overexcited are shifted from each other so as not to overlap each other. Consequently, an increase in the power consumption due to the overlap of the individual overexcitation periods of the plurality of electromagnetic brakes can be prevented. Also, in this example, the electromagnetic brakes are overexcited in order from the electromagnetic brake B6nearest to the hand of the robot arm120. That is, the electromagnetic brake B6nearest to the hand is overexcited first and the electromagnetic brake B1nearest to the base110is excited last. Thus, the power consumption due to the overexcitation can be made even more uniform.

FIG.5is a timing chart showing a control operation in a comparative example. The control operation in the comparative example differs from the control operation in the embodiment shown inFIG.3only in that the cooling fan250and the ventilation fan260are maintained in the ON state during all the periods. The other elements are the same as inFIG.3. In this comparative example, the cooling fan250and the ventilation fan260are maintained in the ON state also in the overexcitation period P2and therefore the power consumption Wc of the control power supply230is higher than in the period P3. The power consumption Wc reaches a maximum value Wc_max2in the overexcitation period P2. This maximum value Wc_max2is greater than the maximum Wc_max1in the embodiment shown inFIG.3.

In the overexcitation period P2, the amount of heat generated in the motor driver circuits221to226is small. Therefore, even if the cooling fan250and the ventilation fan260are stopped, the influence of heat on the motor driver circuits221to226is small. Thus, in the embodiment shown inFIG.3, the cooling ability of the cooling fan250and the ventilation fan260in the overexcitation period P2is made lower than in the period P3and the power consumption is thus reduced. As a result, both the reduction in the power supply capacity of the control power supply230and the cooling of the motor driver circuits221to226can be achieved.

As described above, in the embodiment, as the power consumption of the fans cooling the control device200in the overexcitation period P2, the first power consumption, which is lower than the second power consumption in the period P3after the overexcitation period P2, is employed. Therefore, an excessive increase in the power consumption during the overexcitation period P2can be prevented. Thus, the control power supply230can be reduced in size and cost.

In the embodiment, the control device200controls the operation of the plurality of motors M1to M6and the plurality of electromagnetic brakes B1to B6. However, the numbers of motors and electromagnetic brakes to be controlled can be any number equal to or greater than one.

FIG.6is an explanatory view showing a change in the state of a plurality of electromagnetic brakes in another embodiment. This embodiment differs from the embodiment shown inFIG.4only in that the individual overexcitation periods PP of the electromagnetic brakes partly overlap each other. More specifically, this embodiment is the same as in the embodiment shown inFIG.4in that the timings of overexciting the electromagnetic brakes B1to B6are shifted from each other, but inFIG.6, the individual overexcitation periods PP are shifted from the neighboring individual overexcitation periods PP by half. Even in this way, an increase in the power consumption due to the overlap of all the individual overexcitation periods PP can be prevented. Also, in this example, the length of the entire overexcitation period P2is half the length of the overexcitation period P2shown inFIG.4. Therefore, the robot arm120can be moved earlier.

In the embodiments shown inFIGS.4and6, the restraining effect for the power consumption of the control power supply230in the overexcitation period P2can be achieved by both (i) a first feature of employing the first power consumption, which is lower than the second power consumption in the period P3after the overexcitation period P2, as the power consumption of the fans cooling the control device200, and (ii) a second feature of shifting the individual overexcitation periods PP from each other. Of these, the second feature may be omitted. That is, the individual overexcitation periods PP of the plurality of electromagnetic brakes may be set to overlap each other. However, when both the first feature and the second feature are employed, the restraining effect for the power consumption of the control power supply230can be enhanced further.

Other Aspects

The present disclosure is not limited to the foregoing embodiments and can be implemented according to various aspects without departing from the spirit and scope of the present disclosure. For example, the present disclosure can be implemented according to the aspects described below. A technical feature in the foregoing embodiments corresponding to a technical feature in the aspects described below can be replaced or combined with another where appropriate, in order to solve a part or all of the problems of the present disclosure or in order to achieve a part or all of the effects of the present disclosure. The technical feature can be deleted where appropriate, unless described as essential in this specification.

(1) According to a first aspect of the present disclosure, a control method for a control device controlling a robot arm having a motor braked by an overexcitation-type electromagnetic brake is provided. The control method includes: (a) carrying out overexcitation of the electromagnetic brake; (b) controlling a fan cooling the control device in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

This control method employs the first power consumption, which is lower than the second power consumption after the overexcitation period, as the power consumption of the fan in the overexcitation period. Therefore, the control method can prevent an excessive increase in the power consumption in the overexcitation period.

(2) In the control method, the robot arm may have a plurality of the electromagnetic brakes and a plurality of the motors, and timings of overexciting the electromagnetic brakes may be shifted from each other.

This control method can make the power consumption due to the overexcitation uniform and therefore can restrain the power peak.

(3) In the control method, the plurality of the electromagnetic brakes may be coupled together via a common power line, and the plurality of the electromagnetic brakes may be overexcited in order from the electromagnetic brake nearest to a hand of the robot arm.

This control method can make the power consumption due to the overexcitation even more uniform and therefore can restrain the power peak.

(4) In the control method, the fan may include a ventilation fan exchanging air inside and outside the control device, and the ventilation fan may start operating after the control device accepts, from outside, an instruction to cause the robot arm to operate.

This control method can cause the ventilation fan to operate when ventilation is necessary, and can also restrain the power peak.

(5) In the control method, the control device may have a plurality of the ventilation fans, and in the (b), at least a part of the plurality of the ventilation fans may be stopped.

This control method can lower the power peak further.

(6) In the control method, in the (b), all of the plurality of the ventilation fans may be stopped.

This control method can lower the power peak further.

(7) In the control method, the control device may have a motor driver circuit supplying electric power to the motor. The fan may include a cooling fan blowing air to the motor driver circuit. In the (b), the cooling fan may be stopped.

This control method can prevent an excessive rise in the temperature of the motor driver circuit even if the cooling fan is stopped in the overexcitation period. Therefore, the control method can restrain the power peak.

(8) According to a second aspect of the present disclosure, a non-transitory computer-readable storage medium storing a computer program for control of a control device controlling a robot arm having a motor braked by an overexcitation-type electromagnetic brake is provided. The computer program causes a processor to execute: (a) processing of carrying out overexcitation of the electromagnetic brake and thus switching the electromagnetic brake from a brake active state to a brake release state; (b) processing of controlling a fan cooling the control device in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) processing of controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

(9) According to a third aspect of the present disclosure, a control device controlling a robot arm having a motor braked by an overexcitation-type electromagnetic brake is provided. The control device includes: a motor diver circuit supplying electric power to the motor; a control power supply supplying electric power to the electromagnetic brake; a fan operating when receiving supply of electric power from the control power supply and thus cooling the control device; and a control unit controlling the motor driver circuit and the fan. The control unit executes: (a) processing of carrying out overexcitation of the electromagnetic brake; (b) processing of controlling the fan in such a way that a power consumption of the fan becomes a first power consumption in an overexcitation period during which the overexcitation is carried out; and (c) processing of controlling the fan in such a way that the power consumption of the fan becomes a second power consumption higher than the first power consumption, after the overexcitation period.

The present disclosure can also be implemented according to other aspects than the foregoing aspects. For example, the present disclosure can be implemented according an aspect such as a robot system having a robot and a control device, a computer program for implementing the functions of the control device, and a non-transitory storage medium in which the computer program is recorded.