WO2014117842A1

WO2014117842A1 - A robot controller utilizing a torque margin of a servo motor

Info

Publication number: WO2014117842A1
Application number: PCT/EP2013/051892
Authority: WO
Inventors: Xiaolong Feng; Daniel WÄPPLING; Hans Andersson; Jakob WESTRÖM
Original assignee: Abb Technology Ltd
Priority date: 2013-01-31
Filing date: 2013-01-31
Publication date: 2014-08-07

Abstract

A robot controller (140) comprises at least two parameter sets (80, 90) with configuration parameter values for a robot axis (150).The first parameter set (80) comprises a first torque value τ₁ and a first speed value ω₁, and the second parameter set (90) comprises a second torque value τ₂ and a second speed value ω₂. The robot controller (140) is configured to apply configuration parameter values from a single parameter set (80, 90) at a time. The first torque value τ₁ is smaller than the second torque value τ₂, and the first speed value ω₁ is larger than the second speed value ω₂.The achieved combination of a high torque and a low speed of a servo motor (160) driving the robot axis (150) is useful e.g. during an assembly phase of a work cycle where a high contact force, but not a fast movement, is required. When the parameter values are chosen appropriately, the corresponding operation area of the servo motor (160) can be utilized constantly without shortening the lifetime of an industrial robot (180).

Description

A robot controller utilizing a torque margin of a servo motor

TECHNICAL FIELD

The present invention relates to a robot controller and a method for controlling an industrial robot.

BACKGROUND ART

In an industrial robot, movements of a robot axis are typically implemented by a drive train comprising a servo motor and a gearbox. A robot controller comprises a motor drive for driving the servo motor according to a robot program running in the robot controller. Depending on the robot program and on the payload of the robot, the servo motor generates a certain torque and a certain (angular) speed to move the robot axis. The torque to be generated by the servo motor is many times limited to a value

considerably below the torque capacity of the servo motor; partly the servo motor can be overdimensioned simply because a more suitable motor size is not available, partly the torque may be limited in order to prolong the lifetime of the drive train and the robot as a whole. Similarly, the speed of the servo motor is limited to a certain value below the speed capacity of the servo motor in order to prolong the lifetime of the robot. The limitations of the torque and the speed are done by defining them as configuration parameters for the respective robot axis. The parameter values are stored in a configuration file comprising a torque value and a speed value for each robot axis, and the robot controller takes these values into consideration aiming to avoid exceeding them. Figure 1 shows a torque-speed characteristic curve 10 for a servo motor, and a normal operation area 20 within which the operation of the servo motor is limited by defining a first torque value ii and a first speed value coi that are not supposed to be exceeded. The first torque and speed values ii, (ύι follow from the specifications set on the robot, especially payload, reach, cycle time for a certain

movement, and lifetime. The torque-speed characteristic curve 10 represents the torque capacity and the speed capacity of the servo motor, and both a torque margin 30 in relation to the first torque value ii and a speed margin 40 in relation to the first speed value ωι exist.

Conventionally these margins 30, 40 are not utilized because the robot' s calculated lifetime is based on an assumption that the first torque and first speed values ii, (0i are not exceeded.

EP1878542 discloses a robot control system wherein two different sets of configuration parameter values are used in a robot program. EP1878542 establishes that most robots exceed their calculated lifetime because the tough

specifications used in the calculations do not materialize in reality, and concludes that the specified lifetime can be achieved even when the originally defined configuration parameter values are exceeded, as long as the excess is short. The teaching of EP1878542 corresponds to the high performance operation area 50 of figure 1, defined by the high performance torque value τ_Η and the high performance speed value ω_Η.

The solution of EP1878542 is not desirable in that the periods of time the robot operates in the high performance operation area 50 need to be strongly limited, and the actual performance of the robot is thereby limited. Although a torque margin 30 and a speed margin 40 are available, existing robot systems do not provide a solution where these margins 30, 40 can be constantly utilized without shortening the lifetime of the robot.

SUMMARY OF THE INVENTION One object of the invention is to provide a robot controller that is able to constantly utilize a torque margin of a servo motor in an industrial robot without compromising the lifetime of the robot.

These objects are achieved by the device according to appended claim 1 and the method according to appended claim 10.

The invention is based on the realization that a combination of a high torque and a low speed of a servo motor, if the parameter values are chosen appropriately, does not shorten the lifetime of the robot. Such combination is useful e.g. during an assembly phase of a work cycle where a high contact force, but not a fast movement, is required.

According to a first aspect of the invention, there is provided a robot controller comprising at least two

parameter sets with configuration parameter values for a robot axis. The first parameter set comprises a first torque value Ti and a first speed value coi, and the second parameter set comprises a second torque value i₂ and a second speed value )₂. The robot controller is configured to apply configuration parameter values from a single parameter set at a time. The first torque value ii is smaller than the second torque value i₂, and the first speed value ωι is larger than the second speed value ω₂. By providing two or more alternative parameter sets with appropriate torque and speed values for a robot axis, a torque margin of a servo motor in an industrial robot can be utilized without compromising the lifetime of the robot.

According to one embodiment of the invention, the robot controller comprises at least two parameter sets for each one of a plurality of robot axes. By this measure torque margins of servo motors at a plurality of robot axes can be utilized.

According to one embodiment of the invention, the robot controller comprises at least two parameter sets for each axis of a robot. By this measure torque margins of servo motors at each axis of a robot can be utilized.

According to one embodiment of the invention, the first speed value ωι is at least two times the second speed value (0₂. It is established that with certain drive trains the speed value needs to be reduced considerably before a meaningful increase of the torque value can be allowed.

According to one embodiment of the invention, the second torque value τζ is at least 20 % larger than the first torque value ii, such as at least 30 % or at least 50 % larger than the first torque value T_l. The increased torque value needs to clearly exceed the original torque value, preferably by at least 20 %, in order to have a practical significance .

According to one embodiment of the invention, the robot controller further comprises a program command to activate a parameter set. This is a convenient way to activate a certain parameter set when it is know in advance what parameter values are preferred at what point of a program.

According to one embodiment of the invention, the robot controller further comprises a sensor signal configured to activate a parameter set. This is a convenient way to activate a certain parameter set based on a current need of certain parameter values.

According to one embodiment of the invention, the robot controller further comprises a robot model calculation configured to activate a parameter set. This is a convenient way to activate a certain parameter set based on a current need of certain parameter values.

According to one embodiment of the invention, an industrial robot comprises a robot controller according to the

description hereinbefore. The invention is particularly well adapted to improve the performance of an industrial robot.

According to a second aspect of the invention, there is provided a method for controlling an industrial robot. The method comprises the steps of: defining at least two parameter sets comprising configuration parameter values for a robot axis, the first parameter set comprising a first torque value ii and a first speed value ωι, and the second parameter set comprising a second torque value i₂ and a second speed value ω₂, the first torque value ii being smaller than the second torque value Τ2, and the first speed value coi being larger than the second speed value 0)₂; and applying configuration parameter values from a single parameter set at a time. By providing two or more

alternative parameter sets with appropriate torque and speed values for a robot axis, a torque margin of a servo motor in an industrial robot can be utilized without compromising the lifetime of the robot.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail with reference to the accompanying drawings, wherein figure 1 illustrates a conventional limitation of a servo motor's operation area, figure 2 illustrates a limitation of a servo motor's

operation area according to the invention, figure 3 shows a schematic illustration of an industrial robot according to one embodiment of the invention, and figure 4 shows an example of a movement of a single robot axis . DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to figure 2, according to one embodiment of the invention an operation area of a servo motor is extended to comprise, in addition to a normal operation area 20 defined by a first torque value ii and a first speed value coi, an extended operation area 60 defined by a second torque value T2 and a second speed value o2. The extended operation area 60 provides an increased torque in combination with a low speed. The dimensions of the extended operation area 60 of a servo motor are based on lifetime calculations of a

respective drive train. Since a lifetime of a drive train depends on the construction of the same, it is not possible to give generally applicable dimensions or relations for the extended operation area 60. It is fully possible that for a certain servo motor there are several alternative shapes for the extended operation area 60, the general rule being: the higher the torque the lower the speed.

Referring to figure 3, a schematic illustration of an industrial robot 180 comprising a robot controller 140 according to one embodiment of the invention is shown. A choice between the two operation areas 20, 60 of figure 2 can be done in a robot program 70 by choosing between a first parameter set 80 comprising the first torque value ii and the first speed value coi, and a second parameter set 90 comprising the second torque value i2 and the second speed value (02. The two parameter sets 80, 90 are stored in a configuration file 100 which may comprise corresponding parameter sets 80, 90 for each robot axis 150. The choice between the two parameter sets 80, 90 can be based on an active selection of a robot programmer who uses a program command 170 to activate a certain parameter set 80, 90. The robot programmer may for example know that an increased torque is required at a certain section of a robot task, and activates the second parameter set 90 for that section by applying the respective program command 170. A motor drive 110 comprised within the robot controller 140 generates drive currents to a respective servo motor 160 according to instructions from the robot program 70. The robot controller 140 aims to avoid exceeding the parameter values of the chosen parameter set 80, 90. The choice between the two parameter sets 80, 90 can also be based on a sensor signal indicating that the robot 180 is unable to implement certain movement without an increased torque, or, reversibly, that an increased torque is no longer required. For giving an example, let's assume that the first parameter set 80 with the first torque value ii and the first speed value coi is currently applied, and that there is a torque sensor integrated in the servo motor 160. A real torque value can be derived from the torque sensor' s signal, and the robot controller 140 can be configured to compare the real torque value with the first torque value ii. If the real torque value reaches the first torque value ii but the robot still cannot implement a desired movement, it can be concluded that the available torque is not sufficient. This information can be used to trigger the activation of the second parameter set 90 to increase the torque. Instead of a sensor signal, the comparison can be based on a robot model calculation whereby a mathematical model of the robot and a load is used to derive a real torque value at a robot axis 150.

Figure 4 shows an example of a movement of a single robot axis 150 in a coordinate system with a joint angle φ as an abscissa and a speed ω as an ordinate. The movement

comprises a transfer movement 120 of the robot axis 150 from angle cpi to angle φ2, and an assembly movement 130 from angle Φ2 to angle cp3. During the transfer movement 120 a first parameter set 80 comprising a first torque value ii = 10 Nm and a first speed value ωι = 2n rad/s is applied, and during the assembly movement 130 a second parameter set 90

comprising a second torque value ii = 15 Nm and a second speed value ωι = n rad/s is applied. As a consequence, a relatively fast transfer movement 120 and a relatively high contact force during the assembly movement 130 are achieved. The invention is not limited to the embodiments shown above, but the person skilled in the art may modify them in a plurality of ways within the scope of the invention as defined by the claims. Thus, while the examples shown above only concern a single robot axis 150, it is clear to the person skilled in the art that the invention may be applied on all axes 150 of a robot. The invention is not limited to two parameter sets 80, 90, but three or more parameter sets 80, 90 can be defined for each robot axis 150. Different number of parameter sets 80, 90 can be defined for different robot axes 150.

Claims

1. A robot controller (140) comprising at least two

parameter sets (80, 90) with configuration parameter values for a robot axis (150), the first parameter set (80) comprising a first torque value ii and a first speed value coi, and the second parameter set (90) comprising a second torque value i2 and a second speed value (02, the robot controller (140) being configured to apply configuration parameter values from a single parameter set (80, 90) at a time,

characterized in that the first torque value ii is smaller than the second torque value τ-, and the first speed value <¾ is larger than the second speed value (¾ .

2. A robot controller (140) according to claim 1, wherein the robot controller (140) comprises at least two parameter sets (80, 90) for each one of a plurality of robot axes (150) .

3. A robot controller (140) according to claim 1, wherein the robot controller (140) comprises at least two parameter sets (80, 90) for each axis (150) of a robot.

4. A robot controller (140) according to claim 1, wherein the first speed value (¾ is at least two times the second speed value ω_ζ- .

5. A robot controller (140) according to claim 1, wherein the second torque value τι- is at least 20 % larger than the first torque value , such as at least 30 % or at least 50 % larger than the first torque value ii.

6. A robot controller (140) according to any of the

preceding claims, further comprising a program command (170) to activate a parameter set (80, 90). A robot controller (140) according to any of the preceding claims, further comprising a sensor signal configured to activate a parameter set (80, 90) .

A robot controller (140) according to any of the preceding claims, further comprising a robot model calculation configured to activate a parameter set (80, 90) .

An industrial robot (180) comprising a robot controller (140) according to any of the preceding claims.

A method for controlling an industrial robot (180), the method comprising the steps of:

- defining at least two parameter sets (80, 90)

comprising configuration parameter values for a robot axis (150), the first parameter set (80) comprising a first torque value ii and a first speed value coi, and the second parameter set (90) comprising a second torque value T2 and a second speed value (¾, the first torque value ii being smaller than the second torque value τι-, and the first speed value <¾ being larger than the second speed value (¾; and

- applying configuration parameter values from a single parameter set (80, 90) at a time.