Method of controlling brake, control system and industrial device

Abstract

A method of controlling a brake (22) associated with a joint (18) of an industrial device (10), the method comprising providing (S30), in a control system (20), a stop time value (60) indicative of a stop time (78) throughout which the joint (18) will be in a stopped state (88); determining (S32) by the control system (20) and based on the stop time value (60), whether the brake (22) should switch from a disengaged state (48) to an engaged state (52) within the stop time (78); and controlling (S44), by the control system (20), the brake (22) in accordance with the determination (S32). A control system (20) for controlling a brake (22) associated with a joint (18) of an industrial device (10), and an industrial device (10) comprising the control system (20), are also provided.

Description

[0001] METHOD OF CONTROLLING BRAKE, CONTROL SYSTEM AND INDUSTRIAL DEVICE

[0002] Technical Field

[0003] The present disclosure generally relates to brakes of industrial devices. In particular, a method of controlling a brake associated with a joint of an industrial device, a corresponding control system, and an industrial device comprising the control system, are provided.

[0004] Background

[0005] An industrial robot often spends a significant amount of time waiting in a stationary state while electric motors actively counteract the effects of gravity to maintain position. In such stationary state, energy is not only consumed to power the electric motors, e.g., including powering of a rectifier and an inverter associated with each electric motor, but is also consumed to keep brakes disengaged. Such energy usage contributes substantially to the overall energy consumption of the industrial robot.

[0006] JP H01222877 A discloses a method of controlling a brake of an industrial robot to reduce energy consumption. When the industrial robot is suspended in operation, a timer is operated. When the value of the timer exceeds a time value set in advance, the brake is actuated. The brake is then released in response to a subsequent movement command.

[0007] Summary

[0008] One object of the invention is to provide an improved method of controlling a brake associated with a joint of an industrial device.

[0009] A further object of the invention is to provide an improved control system for controlling a brake associated with a joint of an industrial device.These objects are achieved by the method according to appended claim 1 and by the control system according to appended claim 12.

[0010] The invention is based on the realization that by evaluating a stop time of a joint, if the stop time is sufficiently long to engage the brake, the brake can be engaged directly at a start of the stop time to thereby save energy in comparison with waiting for a timer to expire prior to engaging the brake.

[0011] According to a first aspect, there is provided a method of controlling a brake associated with a joint of an industrial device, the method comprising providing, in a control system, a stop time value indicative of a stop time throughout which the joint will be in a stopped state; determining by the control system and based on the stop time value, whether the brake should switch from a disengaged state to an engaged state within the stop time; and controlling, by the control system, the brake in accordance with the determination.

[0012] The application of the brake within the stop time enables a reduction of energy consumption by the industrial device. By determining that the brake should be engaged based on the stop time value, the brake can be engaged at a start of a long stop time, rather than waiting for a timer to expire prior to engaging the brake. Further energy savings are thereby enabled by the method.

[0013] The method may comprise controlling the brake to engage within the stop time if the stop time value is larger than a threshold time value, and maintaining the brake in the disengaged state throughout the stop time if the stop time value is smaller than the threshold time value.

[0014] Since the determination is made by the control system, the determination is automated, in contrast to being made by a human user. The method thereby provides an ease of use functionality. The stop time may be specified in a program for controlling the industrial device.In the engaged state, the brake holds the joint stationary in the stopped state. In the disengaged state, the brake allows the joint to move. The joint maybe rotational or translational.

[0015] The method may further comprise providing, in the control system, at least one of an engaging time value indicative of an engaging time for the brake to switch from the disengaged state to the engaged state, and a disengaging time value indicative of a disengaging time for the brake to switch from the engaged state to the disengaged state; and determining by the control system and based on at least one of the disengaging time value and the engaging time value, whether the brake should switch to the engaged state within the stop time.

[0016] The method of this variant enables the brake to be seamlessly engaged and disengaged within the stop time without losing any cycle time, i.e., without causing a delay of a subsequent action by the joint after expiry of the stop time. Both energy efficiency and cycle time efficiency can thereby be obtained.

[0017] The method may employ both the engaging time value and the disengaging time value. In alternative variants, the method may employ only one of the engaging time value and the disengaging time value. In these variants, the engaging time value and the disengaging time value may be assumed to have a predetermined relationship, such as being equal. Each of the engaging time and the disengaging time may be at least 0.5 s, such as at least 1 s.

[0018] The method may comprise providing, in the control system, the engaging time value, the disengaging time value and a minimum time value indicative of a minimum time that the brake should adopt the engaged state. In these cases, the method may comprise determining that the brake should switch to the engaged state if the stop time value is larger than a sum of the engaging time value, the disengaging time value and the minimum time value. Thus, in some variants, the threshold time value is constituted by the sum.The minimum time may for example be at least 1 s, such as at least 2 s. The minimum time may be selected to avoid short time periods of the brake being in the engaged state since the energy saving will then be low, and may not motivate the lifetime reduction of the brake caused by engaging the brake.

[0019] The method may further comprise, upon determining that the brake should switch to the engaged state within the stop time, controlling, by the control system, the brake to switch from the disengaged state to the engaged state at a start of the stop time.

[0020] The method may further comprise, upon determining that the brake should switch to the engaged state within the stop time, stopping control, by the control system, of an electric motor associated with the joint within o.i s after the brake adopts the engaged state.

[0021] The method may further comprise, upon determining that the brake should switch to the engaged state within the stop time, controlling, by the control system, the brake to switch from the engaged state to the disengaged state such that the brake adopts the disengaged state at an end of the stop time. The brake may thereby be controlled to start switching from the engaged state to the disengaged state at a time point corresponding to the end of the stop time minus the disengaging time. A subsequent action involving the joint can thereby be performed immediately at the expiry of the stop time while also providing a large energy saving.

[0022] The method may further comprise, upon determining that the brake should switch to the engaged state within the stop time, starting control, by the control system, of an electric motor associated with the joint within o.i s before the brake starts to switch from the engaged state to the disengaged state.

[0023] The method may further comprise determining whether the brake should switch to the engaged state within the stop time based on an estimated energy saving of switching the brake to the engaged state within the stop timein comparison with maintaining the brake in the disengaged state throughout the stop time.

[0024] The method may further comprise comparing the energy saving with a reference value.

[0025] The method may further comprise determining whether the brake should switch to the engaged state within the stop time based on a brake lifetime of the brake. This determination may be made in view of a nominal lifetime of the industrial device, e.g., such that the brake lifetime exceeds the nominal lifetime. In this way, a likelihood that the brake does not have to be replaced during the nominal lifetime is increased. In general, the brake may be controlled such that a remaining useful life of the brake is larger than a remaining useful life of the rest of the industrial device.

[0026] The determination based on the estimation of the brake lifetime may comprise determining a historic mean brake switching frequency of switching the brake; estimating the brake lifetime based on the historic mean brake switching frequency; and providing an updated brake switching frequency of switching the brake for which, together with the historic mean brake switching frequency, the brake lifetime will exceed the nominal lifetime. The brake can then be controlled in accordance with the updated brake switching frequency.

[0027] The historic mean brake switching frequency may be determined as a number of engagements of the brake during a time period, from a start of operation of the industrial device to a current time, divided by this time period. The provision of the updated brake switching frequency may for example comprise providing the updated brake switching frequency as being smaller than the historic mean brake switching frequency if the estimated brake lifetime based on the historic mean brake switching frequency is longer than the nominal lifetime, and vice versa.

[0028] According to a second aspect, there is provided a control system for controlling a brake associated with a joint of an industrial device, the controlsystem comprising at least one data processing device and at least one memory having at least one computer program stored therein, the at least one computer program comprising program code which, when executed by the at least one data processing device, causes the at least one data processing device to provide a stop time value indicative of a stop time throughout which the joint will be in a stopped state; determine based on the stop time value, whether the brake should switch from a disengaged state to an engaged state within the stop time; and control the brake in accordance with the determination.

[0029] The at least one computer program may comprise program code which, when executed by the at least one data processing device, causes the at least one data processing device perform, or command performance of, any operation as described herein, in particular as described in connection with the first aspect. The control system, the brake, the joint and / or the industrial device associated with the second aspect may be of any type described in connection with the first aspect, and vice versa.

[0030] According to a third aspect, there is provided an industrial device comprising the control system according to the second aspect, the joint and the brake. The brake maybe a power-off brake. The industrial device may comprise one or more joints and a brake associated with each joint. The industrial device may be an industrial robot.

[0031] Brief Description of the Drawings

[0032] Further details, advantages and aspects of the present disclosure will become apparent from the following description taken in conjunction with the drawings, wherein:

[0033] Fig. 1: schematically represents an industrial robot comprising a plurality of joints;

[0034] Fig. 2a: schematically represents a cross-sectional side view of one example of a brake in a disengaged state;

[0035] Fig. 2b: schematically represents a cross-sectional side view of the brake inan engaged state;

[0036] Fig. 3: schematically represents components of the industrial robot; Fig.4: schematically represents one example of a diagram of a joint speed of a joint, a brake state of a brake, and power consumption over time;

[0037] Fig. 5: schematically represents a specific method of controlling a brake according to one example;

[0038] Fig. 6: schematically represents a specific method of controlling a brake according to a further example;

[0039] Fig. 7: schematically represents one example of a diagram of the joint speed of the joint, the brake state of the brake, an operational life of the industrial robot, and an operational life of the brake; and Fig. 8: is a flowchart outlining general steps of a method.

[0040] Detailed Description

[0041] In the following, a method of controlling a brake associated with a joint of an industrial device, a corresponding control system, and an industrial device comprising the control system, will be described. The same or similar reference numerals will be used to denote the same or similar structural features.

[0042] Fig. 1 schematically represents a side view of an industrial robot 10. The industrial robot 10 constitutes one example of an industrial device according to the present disclosure. Non-limiting alternative types of industrial devices according to the present disclosure include workpiece positioners and conveyors.

[0043] The industrial robot 10 is exemplified as a seven axis industrial robot but the present disclosure is not limited to this type of robot. An industrial robot according to the present disclosure may comprise at least three axes. As shown in Fig. 1, the industrial robot 10 of this example comprises first to seventh joints i8a-i8g, one or more of which may also be referred to with reference numeral "18". A brake according to the present disclosure maybeprovided at one, several or each of the first to seventh joints i8a-i8g. The industrial robot io further comprises a control system 20, such as a robot controller.

[0044] Fig. 2a schematically represents a cross-sectional side view of one specific and non-limiting example of a brake 22. Such brake 22 is described in international patent application WO 2019161890 Al, the content of which is incorporated herein by reference in its entirety. The brake 22 of this example is a power-off brake, i.e., the brake 22 stops or holds a load when electric power is either accidentally lost or intentionally disconnected. The brake 22 serves to counteract relative rotational movement 24 around a rotation axis 26 between a second member 28 and a first member 30. Brakes according to the present disclosure are however not limited to power-off brakes or to rotational brakes. In Fig. 2a, current is applied to the brake 22 such that the brake 22 adopts a disengaged state 48.

[0045] Fig. 2b schematically represents a cross-sectional side view of the brake 22 in an engaged state 52 when no current is applied to the brake 22. An engaging time for the brake 22 to switch from the disengaged state 48 to the engaged state 52, and a disengaging time for the brake 22 to switch from the engaged state 52 to the disengaged state 48 may be determined in various ways known to the skilled person, e.g., by using a sensor (not illustrated) monitoring the position of a component of the brake 22, or by monitoring the current and / or the voltage supplied to an electric motor associated with the brake 22.

[0046] Fig. 3 schematically represents exemplifying components of the industrial robot 10 of Fig. 1. The control system 20 of this example comprises a data processing device 54 and a memory 56. The memory 56 has a computer program stored therein. The computer program comprises program code which, when executed by the data processing device 54, causes the data processing device 54 to perform, or command performance of, various operations as described herein. The computer program of this example is a robot program 58 for controlling the industrial robot 10 is provided in the memory 56.The memory 56 contains a stop time value 60 indicative of a duration of a stop time throughout which one or more joints 18 will be in a stopped state, an engaging time value 62 indicative of the engaging time and a disengaging time value 64 indicative of the disengaging time. The memory 56 of this example further contains a minimum time value 66 indicative of a minimum time 84, see Fig. 4, that the brake 22 may adopt the engaged state 52. The robot program 58 of this example includes a plurality of alternating cycles and stop times.

[0047] The components in Fig. 3 are illustrated as comprising first to n'th joints 18a-i8n, associated first to n'th brakes 22a-22n, associated first to n'th electric motors 68a-68n, and associated first to n'th transmissions yoa-yon, such as gearboxes, where n is a positive integer. One, several or all of the first to n'th brakes 22a-22n, one, several or all of the first to n’th electric motors 68a-68n, and one, several or all of the first to n'th transmissions yoa-yon may also be referred to with reference numerals "22", "68" and "yo", respectively.

[0048] Fig. 4 schematically represents one example of a diagram of a joint speed y2 of a joint 18, a brake state y4 of a brake 22, and power consumption y6 of the industrial robot 10 over time t. In Fig. 4, the stop time y8, the engaging time 80, the disengaging time 82 and the minimum time 84 can also be seen. Although descriptions are mainly given with respect to a single brake 22 and a single joint 18 herein, these descriptions also apply for a control of a plurality of brakes and associated joints 18, such as all brakes and associated joints 18 of the industrial robot 10. Thus, instead of controlling only one single brake 22, several or all brakes 22 maybe controlled in accordance with the method. This may or may not lead to a simultaneous engagement and a simultaneous disengagement of the brakes 22.

[0049] Fig. 4 shows three power levels P1-P3 of the power consumption y6 according to one example. A first power level Pi represents a power consumption y6 by the industrial robot 10 when no power is supplied to any of the brake 22 and the associated electric motor 68. A second power level P2 represents a power consumption y6 by the industrial robot 10 when no power is supplied to thebrake 22 but power is supplied to the associated electric motor 68. A third power level P3 represents a power consumption 76 by the industrial robot 10 when power is supplied to both the brake 22 and the associated electric motor 68. Each of the first to third power levels P1-P3 can be determined by measurements or by calculations. Fig. 4 further shows an energy saving Es obtained by engaging the brake 22 within the stop time 78 in comparison with not engaging the brake 22 within the stop time 78.

[0050] At a time to, the joint 18 is in a moving state 86, the brake 22 is in the disengaged state 48 and the power consumption 76 is at the third power level P3. Thus, at the time to, power is supplied to both the brake 22 and the electric motor 68.

[0051] At a time ti, the joint 18 starts decelerating from the moving state 86 towards the stopped state 88.

[0052] At a time t2, the joint 18 reaches the stopped state 88 where the joint speed 72 is zero. Thus, the stop time 78 starts at the time t2. At the same time, the control system 20 commands the brake 22 to switch from the disengaged state 48 to the engaged state 52, here by stopping the power supply to the brake 22. The power consumption 76 thereby decreases from the third power level P3 to the second power level P2 at the time t2.

[0053] At a time t3, the brake 22 adopts the engaged state 52. At the same time, the control system 20 stops the power supply to the electric motor 68. The power consumption 76 thereby decreases from the second power level P2 to the first power level Pi at the time t3. A time from time t2 to time t3 corresponds to the engaging time 80.

[0054] A time t4 represents a time corresponding to the minimum time 84 after the time t3. The minimum time 84 may for example be at least 1 s. At the time t4, the power consumption 76 is at the first power level Pi.

[0055] At a time t5, the control system 20 commands the brake 22 to switch from the engaged state 52 to the disengaged state 48, here by supplying power tothe brake 22. At the same time, the control system 20 starts supplying power to the electric motor 68 (to hold the electric motor 68 stationary when the braking by the brake 22 becomes released). The power consumption 76 thereby rises from the first power level Pi to the third power level P3 at the time ts. A time of the brake 22 in the engaged state 52, between the times t3 and ts, is denoted as 90 in Fig. 4.

[0056] At a time t6, the brake 22 adopts the disengaged state 48. At the same time, the control system 20 commands the joint 18 to start accelerating. Thus, the stop time 78 ends at the time t6. A time from time ts to time t6 corresponds to the disengaging time 82. At the time t6, the power consumption 76 is at the third power level P3.

[0057] The robot program 58 of this example includes a plurality of wait instructions, such as the instruction "WaitTime" in the programming language RAPID by ABB. Each wait instruction defines a stop time 78 that the robot program 58 waits during execution of the instruction before continuing to a next instruction. The stop time 78 may be set in seconds and may be a constant or variable value. With the method according to the invention, the wait instructions can be enhanced, for example to reduce energy consumption without losing cycle time.

[0058] When the stop time 78 amounts to at least a sum of the engaging time 80 and the disengaging time 82, it can be concluded that the brake 22 can be switched from the disengaged state 48 to the engaged state 52 and back to the disengaged state 48 during the stop time 78 without losing cycle time, i.e., without the start of movement of the joint 18 at the time t6 having to be delayed due to the brake 22 not being in the disengaged state 48. However, if the brake 22 adopts the engaged state 52 only during a very short time period, the energy saving Es will be very small and may therefore be considered to not motivate the cost of a reduced remaining useful life of the brake 22 due to the switching thereof.In this example, it is assumed that the stop time 78 is known from the robot program 58. In case the stop time 78 is unknown, the brake 22 may be switched to the engaged state 52 after expiry of a predefined time period. Such time period may for example be at least two seconds.

[0059] At the end of the stop time 78 at the time t6, the brake 22 adopts the disengaged state 48 such that the joint 18 can initiate an action immediately at the time t6 without any delay caused by the disengagement of the brake 22. Thus, neither the engaging time 80 nor the disengaging time 82 adds to the overall cycle time. In general, the control system 20 may be said to be programmed to determine whether it is worth applying the brake 22 within the stop time 78. By considering the engaging time 80 and the disengaging time 82 when determining whether the brake should be engaged during a stop time 78, energy consumption can be reduced (by engaging the brake 22) without risking a delayed start of a next cycle.

[0060] Fig. 5 schematically represents a specific method of controlling the brake 22 according to one example corresponding to Fig. 4. The method starts with initiation S10 of a wait instruction that includes a specified stop time 78, when a current time tcurrent is at a start time tstart of the stop time 78, such as at the time t2. After the initiation S10, the method proceeds by determining S12, by the control system 20, whether the stop time 78 meets the following condition (1):

[0061]

[0062] >

[0063] where Tstop is the stop time 78 in seconds, Tbrakeon is the engaging time 80 in seconds, Tbrakemin is the minimum time 84 in seconds and Tbrakeoff is the disengaging time 82 in seconds. The stop time 78 is thereby evaluated in view of the engaging time 80, the disengaging time 82 and the minimum time 84.

[0064] If the stop time Tstop meets the condition (1), the method proceeds by commanding S14, by the control system 20, engagement of the brake 22.The method proceeds by determining S16, by the control system 20, whether the current time tcurrent meets the following condition (2):

[0065]

[0066] If the current time tcurrent does not meet the condition (2), the determination S16 is repeated. If the current time tcurrent meets the condition (2), the method proceeds by commanding S18, by the control system 20, disengagement of the brake 22.

[0067] The method proceeds by determining S20, by the control system 20, whether the current time tcurrent meets the following condition (3):

[0068]

[0069] If the current time tcurrent does not meet the condition (3), the determination S20 is repeated. Moreover, if it is determined S12 that the stop time Tstop does not meet the condition (1), the method proceeds to the determination S20. If the current time tcurrent meets the condition (3), the method proceeds by commanding S22, by the control system 20, the joint 18 to perform an action.

[0070] Fig. 6 schematically represents a specific method of controlling the brake 22 according to a further example. Mainly differences with respect to Fig. 5 will be described. In the method of the example in Fig. 6, the energy saving Es obtained by engaging the brake 22 within the stop time 78 is considered, rather than the minimum time 84 in Fig. 5. Consideration of the energy saving Es may be made conditional on the third power level P3 being larger than the second power level P2 when the joint 18 is in the stopped state 88. The energy saving Es can be expressed with formula (4) as:

[0071] , ^brak.eonxP^~^ Tstop ~ (Tbrak.eon^'^brak.eoff))xP^f. Cc = 1 - - - - - (4J (Tstop ~Tbrakeoff)

[0072] where the energy saving Es is a unitless figure representing a relative energy saving.As the stop time 78 increases, formula (4) converges towards formula (5):

[0073]

[0074] After the initiation S10, the method proceeds by determining S24, by the control system 20, whether the energy saving Es meets the following condition (6):

[0075] ES —Emin ( )

[0076] where Emin is a positive and non-zero reference value representing a minimum relative energy saving. Thus, the control is based on the principle that the energy saving Es has to amount to at least the reference value Emin if it should be worth applying the brake 22 within the stop time 78. If the method is used for each of the plurality of brakes 22 individually, a brake 22 of a large joint 18 that works against gravity (e.g., the third joint 18c in the position of the industrial robot 10 in Fig. 1) may be more likely to be engaged than the brakes 22 of small or vertical joints 18 with this principle. Thus, the method of the invention can lead to different outcomes for different brakes 22.

[0077] If the energy saving Es meets the condition (6), the method proceeds by commanding S14, by the control system 20, engagement of the brake 22. If the energy saving Es does not meet the condition (6), the method proceeds to the determination S20.

[0078] The methods in Figs. 5 and 6 may be combined. For example, both conditions (1) and (6) may have to be fulfilled in order to proceed to the commanding S14 of the engagement of the brake 22.

[0079] Fig. 7 schematically represents one example of a diagram of the joint speed 72 of the joint 18, the brake state 74 of the brake 22, an operational life 92 of the industrial robot 10, and a brake operational life 94 of the brake 22. Fig. 7 shows a nominal lifetime 96 of the industrial robot 10 and a brake lifetime 98 of the brake 22. At each point in time, a remaining useful life of the industrialrobot io may be expressed as the nominal lifetime 96 minus the operational life 92, and a remaining useful life of the brake 22 may be expressed as the brake lifetime 98 minus the brake operational life 94. Fig. 7 further shows a plurality of cycles 100, where each cycle 100 includes an action of the joint 18 (where the joint 18 is in the moving state 86) and a stop time 78.

[0080] As with any mechanical component, the brake lifetime 98 is limited. Thus, the brake 22 can only undergo a certain number of disengaging / engaging sequences before failure. The brake lifetime 98 of the brake 22 can be determined in various ways, for example by previous experience. If a frequency of switching the brake 22 is known, the brake lifetime 98 may be expressed in time. In any case, the brake lifetime 98 may be expressed as a number of disengaging / engaging sequences.

[0081] It may be intended that the brake lifetime 98 should not limit the nominal lifetime 96. The nominal lifetime 96 may be considered as the minimum lifetime of the components that constitute the industrial robot 10. For example, it may be intended that the transmission 70 should fail before the brake 22 and should dictate the nominal lifetime 96, which may for example be 40000 hours.

[0082] From a time tn to a time ti2, the brake 22 is switched to the engaged state 52 in each stop time 78. The control system 20 determines a historic mean brake switching frequency 102 in this time period as the number of engagements of the brake 22 during this time period divided by the time period. Although this time period is illustrated as containing three cycles 100, this time period may contain much more cycles 100, such as several hundred cycles 100.

[0083] Based on the historic mean brake switching frequency 102, the control system 20 determines a time when the brake operational life 94 reaches the brake lifetime 98, which in Fig. 7 is at a time ti3. Since the time ti3 is before a time ti4 when the operational life 92 of the industrial robot 10 reaches the nominal lifetime 96, it can be concluded that a continued operation of the brake 22 with the historic mean brake switching frequency 102 will lead to areduction of the lifetime of the industrial robot io. The control system 20 therefore provides an updated brake switching frequency 104 of switching the brake 22 such that the brake operational life 94 will reach the brake lifetime 98 at a time later than the time when the operational life 92 of the industrial robot 10 reaches the nominal lifetime 96, e.g., with a certain margin. The margin may for example be defined such that the brake operational life 94 is less than 95 % of the brake lifetime 98 at the time when the operational life 92 of the industrial robot 10 reaches the nominal lifetime 96 (the time t4 in Fig. 7). As illustrated in Fig. 7, when the brake 22 is controlled in accordance with the updated brake switching frequency 104, the brake 22 is not switched to the engaged state 52 in each stop time 78.

[0084] Fig. 8 is a flowchart outlining general steps of a method. The method may comprise providing S26, in a control system 20, at least one of an engaging time value 62 indicative of an engaging time 80 for the brake 22 to switch from a disengaged state 48 to an engaged state 52, and a disengaging time value 64 indicative of a disengaging time 82 for the brake 22 to switch from the engaged state 52 to the disengaged state 48. The provision S26 may comprise providing S28, in the control system 20, the engaging time value 62, the disengaging time value 64 and a minimum time value 66 indicative of a minimum time 84 that the brake 22 should adopt the engaged state 52.

[0085] The method further comprises providing S30, in the control system 20, a stop time value 60 indicative of a stop time 78 throughout which the joint 18 will be in a stopped state 88.

[0086] The method further comprises determining S32 by the control system 20 and based on the stop time value 60, whether the brake 22 should switch to the engaged state 52 within the stop time 78.

[0087] The determination S32 may comprise determining S33 by the control system 20 and based on at least one of the disengaging time value 64 and the engaging time value 62, whether the brake 22 should switch to the engaged state 52 within the stop time 78.The determination S33 may comprise determining S12 that the brake 22 should switch to the engaged state 52 if the stop time value 60 is larger than a sum of the engaging time value 62, the disengaging time value 64 and the minimum time value 66.

[0088] Alternatively, or in addition, the determination S32 may comprise determining S34 whether the brake 22 should switch to the engaged state 52 within the stop time 78 based on an estimated energy saving Es of switching the brake 22 to the engaged state 52 within the stop time 78 in comparison with maintaining the brake 22 in the disengaged state 48 throughout the stop time 78. The determination S34 may comprise comparing S24 the energy saving Es with a reference value Emin.

[0089] The determination S32 may comprise determining S36 whether the brake 22 should switch to the engaged state 52 within the stop time 78 based on a brake lifetime 98 of the brake 22. The determination S36 may comprise determining S38 a historic mean brake switching frequency 102 of switching the brake 22; estimating S40 the brake lifetime 98 based on the historic mean brake switching frequency 102; and providing S42 an updated brake switching frequency 104 of switching the brake 22 for which, together with the historic mean brake switching frequency 102, the brake lifetime 98 will exceed the nominal lifetime 96.

[0090] The method further comprises controlling S44, by the control system 20, the brake 22 in accordance with the determination S32. The control S44 may comprise controlling S46, by the control system 20, the brake 22 to switch from the disengaged state 48 to the engaged state 52 at a start of the stop time 78. Alternatively, or in addition, the control S44 may comprise controlling S48, by the control system 20, the brake 22 to switch from the engaged state 52 to the disengaged state 48 such that the brake 22 adopts the disengaged state 48 at an end of the stop time 78.

[0091] The method may further comprise, upon determining S32 that the brake 22 should switch to the engaged state 52 within the stop time 78, stoppingcontrol S50, by the control system 20, of an electric motor 68 associated with the joint 18 within 0.1 s after the brake 22 adopts the engaged state 52.

[0092] The method may further comprise, upon determining S32 that the brake 22 should switch to the engaged state 52 within the stop time 78, starting control S52, by the control system 20, of an electric motor 68 associated with the joint 18 within 0.1 s before the brake 22 starts to switch from the engaged state 52 to the disengaged state 48.

[0093] While the present disclosure has been described with reference to exemplary embodiments, it will be appreciated that the present invention is not limited to what has been described above. For example, it will be appreciated that the dimensions of the parts may be varied as needed. Accordingly, it is intended that the present invention may be limited only by the scope of the claims appended hereto.

Claims

CLAIMS1. A method of controlling a brake (22) associated with a joint (18) of an industrial device (10), the method comprising:- providing (S30), in a control system (20), a stop time value (60) indicative of a stop time (78) throughout which the joint (18) will be in a stopped state (88);- determining (S32) by the control system (20) and based on the stop time value (60), whether the brake (22) should switch from a disengaged state (48) to an engaged state (52) within the stop time (78); and- controlling (S44), by the control system (20), the brake (22) in accordance with the determination (S32).

2. The method according to claim 1, further comprising:- providing (S26), in the control system (20), at least one of an engaging time value (62) indicative of an engaging time (80) for the brake (22) to switch from the disengaged state (48) to the engaged state (52), and a disengaging time value (64) indicative of a disengaging time (82) for the brake (22) to switch from the engaged state (52) to the disengaged state (48); and- determining (S33) by the control system (20) and based on at least one of the disengaging time value (64) and the engaging time value (62), whether the brake (22) should switch to the engaged state (52) within the stop time (78).

3. The method according to claim 2, wherein the method comprises providing (S28), in the control system (20), the engaging time value (62), the disengaging time value (64) and a minimum time value (66) indicative of a minimum time (84) that the brake (22) should adopt the engaged state (52); and determining (S12) that the brake (22) should switch to the engaged state (52) if the stop time value (60) is larger than a sum of the engaging time value (62), the disengaging time value (64) and the minimum time value (66).4- The method according to any of the preceding claims, further comprising, upon determining (S32) that the brake (22) should switch to the engaged state (52) within the stop time (78), controlling (S46), by the control system (20), the brake (22) to switch from the disengaged state (48) to the engaged state (52) at a start (t2) of the stop time (78).

5. The method according to any of the preceding claims, further comprising, upon determining (S32) that the brake (22) should switch to the engaged state (52) within the stop time (78), stopping control (S50), by the control system (20), of an electric motor (68) associated with the joint (18) within 0.1 s after the brake (22) adopts the engaged state (52).

6. The method according to any of the preceding claims, further comprising, upon determining (S32) that the brake (22) should switch to the engaged state (52) within the stop time (78), controlling (S48), by the control system (20), the brake (22) to switch from the engaged state (52) to the disengaged state (48) such that the brake (22) adopts the disengaged state (48) at an end (t6) of the stop time (78).

7. The method according to any of the preceding claims, further comprising, upon determining (S32) that the brake (22) should switch to the engaged state (52) within the stop time (78), starting control (S52), by the control system (20), of an electric motor (68) associated with the joint (18) within 0.1 s before the brake (22) starts to switch from the engaged state (52) to the disengaged state (48).

8. The method according to any of the preceding claims, further comprising determining (S34) whether the brake (22) should switch to the engaged state (52) within the stop time (78) based on an estimated energy saving (Es) of switching the brake (22) to the engaged state (52) within the stop time (78) in comparison with maintaining the brake (22) in the disengaged state (48) throughout the stop time (78).

9. The method according to claim 8, further comprising comparing (S24) the energy saving (Es) with a reference value (Emin).

10. The method according to any of the preceding claims, further comprising determining (S36) whether the brake (22) should switch to the engaged state (52) within the stop time (78) based on a brake lifetime (98) of the brake (22).

11. The method according to claim 10, wherein the determination (S36) based on the estimation of the brake lifetime (98) comprises:- determining (S38) a historic mean brake switching frequency (102) of switching the brake (22);- estimating (S40) the brake lifetime (98) based on the historic mean brake switching frequency (102); and- providing (S42) an updated brake switching frequency (104) of switching the brake (22) for which, together with the historic mean brake switching frequency (102), the brake lifetime (98) will exceed the nominal lifetime (96).

12. A control system (20) for controlling a brake (22) associated with a joint (18) of an industrial device (10), the control system (20) comprising at least one data processing device (54) and at least one memory (56) having at least one computer program stored therein, the at least one computer program comprising program code which, when executed by the at least one data processing device (54), causes the at least one data processing device (54) to:- provide (S30) a stop time value (60) indicative of a stop time (78) throughout which the joint (18) will be in a stopped state (88);- determine (S32) based on the stop time value (60), whether the brake (22) should switch from a disengaged state (48) to an engaged state (52) within the stop time (78); and- control (S44) the brake (22) in accordance with the determination (S32).2213- An industrial device (10) comprising the control system (20) according to claim 12, the joint (18) and the brake (22).

14. The industrial device (10) according to claim 13, wherein the brake (22) is a power-off brake.

15. The industrial device (10) according to claim 13 or 14, wherein the industrial device (10) is an industrial robot.

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