Method and device for decelerating a robot axis arrangement

Abstract

A method for decelerating a robot axis arrangement having at least one output link includes steps of applying a braking force on the output link with a brake and, in so doing, controlling a driving force of a drive that acts on the output link, and/or controlling the braking force on the basis of a dynamic variable of the output link, wherein the dynamic variable is a function of the braking force.

Claims

1. A method for decelerating a robot axis arrangement comprising at least one output link, the method comprising: applying a braking force on the output link with a brake; while applying the braking force, controlling a driving force of a drive that acts on the output link on the basis of a dynamic variable of the output link, wherein the dynamic variable depends on the braking force; wherein the drive at least temporarily is controlled to decelerate the output link in order to exert a braking effect; and wherein the braking force and the driving force are controlled in parallel branches or through parallel channels.

2. The method of claim 1, further comprising: detecting the dynamic variable of the output link using a force sensor operatively connected to the output link; and controlling at least one of the braking force or the driving force on the basis of the dynamic variable of the output link, wherein the dynamic variable comprises at least one of a force or a movement variable.

3. The method of claim 1, wherein at least one of the driving force or the braking force is controlled on the basis of a difference between the dynamic variable and a specified limit value.

4. The method of claim 1, wherein the braking force is applied on the basis of an operating exception.

5. The method of claim 1, wherein the brake includes a holding brake for locking the output link.

6. The method of claim 5, wherein the holding brake is a mechanical, hydraulic, or pneumatic holding brake.

7. The method of claim 1, wherein at least one of the drive or the brake is monitored with fail-safe technology.

8. The method of claim 1, wherein: at least one of the dynamic variable or at least one control variable for controlling at least one of the driving force or the braking force is determined with fail-safe technology; or at least one of the driving force or the braking force is controlled with fail-safe technology; or at least one of the dynamic variable or at least one control variable for controlling at least one of the driving force or the braking force is determined with fail-safe technology, and at least one of the driving force or the braking force is controlled with fail-safe technology.

9. The method of claim 1, wherein the dynamic variable comprises a torque.

10. The method of claim 2, wherein at least one of the driving force or the braking force is controlled on the basis of a difference between the dynamic variable and a specified limit value.

11. The method of claim 2, wherein the braking force is applied on the basis of an operating exception.

12. The method of claim 2, wherein the brake includes a holding brake for locking the output link.

13. The method of claim 12, wherein the holding brake is a mechanical, hydraulic, or pneumatic holding brake.

14. The method of claim 2, wherein at least one of the drive or the brake is monitored with fail-safe technology.

15. The method of claim 2, wherein: at least one of the dynamic variable or at least one control variable for controlling at least one of the driving force or the braking force is determined with fail-safe technology; or at least one of the driving force or the braking force is controlled with fail-safe technology; or at least one of the dynamic variable or at least one control variable for controlling at least one of the driving force or the braking force is determined with fail-safe technology, and at least one of the driving force or the braking force is controlled with fail-safe technology.

16. The method of claim 2, wherein the dynamic variable comprises a torque.

17. The method of claim 2, wherein the movement variable comprises an acceleration of the output link.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1: a portion of a robot axis arrangement according to one embodiment of the present invention.

(2) FIG. 2: a method for decelerating the robot axis arrangement from FIG. 1 according to one embodiment of the present invention.

(3) FIG. 3: a portion of a control means of the robot axis arrangement from FIG. 1 according to an additional embodiment of the present invention; and

(4) FIGS. 4A, 4B, 4C: progressions of a torque in the robot axis arrangement from FIG. 1.

DETAILED DESCRIPTION

(5) FIG. 1 shows an axis A of a robot axis arrangement according to one embodiment of the present invention. The axis can be, for example, a base axis or an arm axis of a six-axis or multi-axis industrial or light-weight robot. Other axis of the robot, which are otherwise not shown, can be constructed and decelerated in the same way, as described below with reference to the axis A, described herein.

(6) The robot axis has an output link in the form of an output shaft 1 of a gear unit 4.3, 4.4 of an axis drive, which output shaft is connected in a rotationally and axially rigid manner to the robot link 2.1, which is pivot-mounted on an additional robot link 2.2 by means of the output shaft by way of the bearing 3.

(7) In order to apply a driving force on the output shaft, an electric motor is provided having a stator 4.1 and a rotor 4.2, which is coupled to the output shaft 1 by means of the gears 4.3, 4.4 of the gear unit.

(8) In order to apply a braking force on the output shaft, an additional brake having a spring element 5.1, for tightening a rotor-fixed braking member in the form of a brake disk 5.2 and a multi-part braking member in the form of brake pads 5.3 against each other, and an electromagnetic actuator 5.4 for spacing the braking members 5.2, 5.3 apart from each other and/or for an actively controlled venting of the brake, is disposed on the side (to the right in FIG. 1) of the drive motor 4.1, 4.2 that faces away from the gear unit.

(9) In one modification (not shown) the brake can be disposed between the drive motor and the gear unit or on a side of the drive gear unit (to the left in FIG. 1) that faces away from the motor. In addition or alternatively, the gear unit can be designed as a harmonic drive gear unit.

(10) The brake is designed as a holding brake for locking the output shaft 1 as a brake, which is closed without power and which is opened and/or vented by supplying energy to the electromagnets 5.4 in the normal operating mode.

(11) A control means for controlling the driving force and/or the braking force of the axis A of the robot is implemented in an axis control unit 6, which is disposed in the additional robot link 2.2, in which the drive and the brake are disposed.

(12) A detection means in the form of a torque sensor 7 for detecting a dynamic variable in the form of a torque T is disposed between the robot link 2.1 and the output shaft 1, is mounted on said output shaft and is signal-connected to the axis control unit 6. Both the torque determination and the control of the drive and the brake by means of the axis control unit are designed in fail-safe technology, in particular, through redundancy, preferably diversity.

(13) FIG. 2 shows a method for decelerating the robot axis arrangement from FIG. 1 according to one embodiment of the present invention, in particular, how this method is carried out by means of the control means in the form of the axis control unit 6.

(14) In a step S10, the axis control unit 6 controls the actuator 5.4 of the brake on the basis of an operating exception, for example, an emergency stop N, in order to apply a braking torque T.sub.B,s. As a result, the additional holding brake for stopping the axis A as a consequence of an emergency stop (S10: Y) is closed.

(15) In particular, in such a situation, the structure of the robot and/or the brake can be subjected to a high dynamic load: as soon as the brake closes, the output shaft 1 is loaded for a short time with the full inertia of the axis A, in particular, the full inertia of the robot link 2.1, which is moving at a high speed.

(16) Therefore, in a step S20, when the brake is closed, in particular, during the entire deceleration up to a standstill of the axis A, the target driving torque T.sub.M,s of the electric motor 4.1, 4.2 is specified on the basis of the torque T, which acts in the output shaft 1 and is determined by the torque sensor 7, which torque in turn is a function of the current actual braking force T.sub.B,i.

(17) In one embodiment, the target driving torque T.sub.M,s is specified, for example, in proportion to a difference =T.sub.max|T| between the torque T and a specified limit value T.sub.max:
T.sub.M,s=.sub.M(T.sub.M,i,)
with the current actual driving torque T.sub.M,i and with a function .sub.M, which is stored in the axis control unit 6, which function .sub.M, upon exceeding the limit value T.sub.max, i.e., <0, applies a driving torque, which acts in the opposite direction of the brake and counteracts the delay of the axis A. By this means, the deceleration is delayed and thus the load is reduced. In other words, the electric motor 4.1, 4.2 compensates for a portion of the braking torque of the closed brake 5.1-5.4 and thus reduces the delay of the axis A and, thereby, in particular, the load on the output shaft 1. This can be every advantageous, in particular if the brake can only be opened and closed completely without being able to specify the braking force in between.

(18) If, on the other hand, the braking force can be controlled, then in addition or alternatively, the axis control unit 6 can also correspondingly control the brake, for example, in accordance with a function .sub.B, which is stored in the axis control unit 6 and which, on exceeding the limit value T.sub.max, i.e., <0 reduces the braking torque. By this means, the deceleration is likewise delayed and, thus, the load is reduced.
T.sub.B,s=.sub.B(T.sub.B,i,)

(19) The functions .sub.M, .sub.B can include a model, in particular, a dynamic model of the robot axis arrangement, in order to consider the dynamics of the robot axis arrangement, in particular, its inertia. The actual driving torque T.sub.M,i and/or the actual braking torque T.sub.B,i can be measured, for example, or can be estimated by an observer. In an additional embodiment, it can also remain unconsidered, i.e., T.sub.M,s=.sub.M() and/or T.sub.B,s=.sub.B().

(20) The braking force and the driving force T.sub.B,i, T.sub.M,i have an accumulative effect in the output shaft 1. The load on the output shaft 1, the bearings 3, etc. is reduced by adjusting downwards, at least in phases, the braking torque by means of the corresponding target values T.sub.B,s and/or by compensating to some extent by specifying the corresponding inverse target value T.sub.M,s for the drive:
T=T.sub.B,i+T.sub.M,iT.sub.B,s+T.sub.M,s

(21) A very simple function .sub.B can implement, for example, a proportional control:

(22) $T_{B,s}=\{\begin{array}{c}{T}_{B,\max }+K_p.Math.<0,\\ T_{B,\max }0\end{array}$

(23) with the proportional gain K.sub.p and the maximum braking torque T.sub.B,max, which is applied, as long as the torque T, determined by the torque sensor 7, in the output shaft 1 does not exceed the limit value T.sub.max. A very simple function .sub.M can be formed in the same way, in order to reduce the entire torque T in the output shaft 1.

(24) FIG. 3 shows a portion of a control means of the robot axis arrangement from FIG. 1 according to a modification of the above described embodiment.

(25) In this modification, the control means 6 has a speed controller 6.1, which in the event of an emergency stop N determines a target braking torque T.sub.s (for example, in proportion to the actual speed to be reduced (T.sub.s=K.sub.p ni) and limited to a maximum amount (T.sub.s<T.sub.s,max)) from the difference between the target and the actual speed n.sub.i of the output shaft 1 and supplies said target braking torque to a torque controller 6.2. The torque controller 6.2 compares the actual torque T, detected by the torque sensor 7, in the output shaft with this target braking torque Ts and provides a corresponding target current value, after limiting to a maximum value, to a current controller 6.3, which in turn supplies the stator 4.1 of the electric motor.

(26) In parallel to this branch, the control means 6 has a brake control unit 6.4, which closes the brake 5.1-5.4 in the event that an emergency stop N has been detected.

(27) FIGS. 4A to 4C show temporal progressions of the torque T (dashed-dotted line in FIG. 4) as well as the actual torques T.sub.M,i (solid line in FIG. 4) and T.sub.B,i (dashed line in FIG. 4) of the electric motor and/or the brake in the robot axis arrangement from FIG. 1, as implemented by the control means 6 from FIG. 3. An emergency stop N is thereby initiated at time t=0 in each instance.

(28) In the example shown in FIG. 4A, the speed controller 6 commands, on the basis of the difference between the actual speed and the target speed 0, a maximum target braking torque T.sub.s,max, which the torque controller 6.2 endeavors to generate by means of a corresponding decelerating control of the electric motor. Correspondingly, the actual torque T.sub.M,i of the electric motor initially increases sharply.

(29) With the inertia-induced delay, the brake control unit 6.4 also closes the brake 5.1-5.4, so that the actual torque T.sub.B,i of the brake also increases after a time delay. Due to the mechanical accumulative effect of both actual torques T.sub.M,i and T.sub.B,i, a short term overshooting of the torque T occurs in the output shaft 1. This is detected by the torque sensor 7. The torque controller 6.2 correspondingly reduces the braking torque, which is applied by the electric motor, as a result, the brake substantially takes over the deceleration of the output shaft and is supported in this by the drive that acts in the same direction.

(30) In the example shown in FIG. 4B, the applied brake exerts a stronger braking torque, which would lead to a long term exceeding of a permissible braking torque in the output shaft 1. Correspondingly, the torque controller 6.2 here applies a torque, using the electric motor, in the opposite direction of the torque of the brake.

(31) In the example shown in FIG. 4C, the drive is allowed to act only in the same direction. Correspondingly, the torque controller 6.2 reduces the torque, which is to be generated by the electric motor, to zero.

(32) While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features shown and discussed herein may be used alone or in combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicants' general inventive concept.

LIST OF REFERENCES

(33) A robot axis N emergency stop (operating exception) 1 output shaft (output link) 2.1, 2.2 robot link 3 bearing 4.1 stator 4.2 rotor 4.3, 4.4 gears (gear unit) 5.1 spring 5.2 brake disk (brake member) 5.3 brake pad (brake member) 5.4 electromagnet (actuator) 6 axis control unit (control means) 6.1 speed controller 6.2 torque controller 6.3 current controller 6.4 brake control unit 7 torque sensor (detection means)