US20050046376A1

US20050046376A1 - System for collision avoidance of rotary atomizer

Info

Publication number: US20050046376A1
Application number: US10/895,430
Authority: US
Inventors: Sven Hooge; Dietmar Wildermuth
Original assignee: Behr Systems Inc
Current assignee: Duerr Systems Inc
Priority date: 2002-09-30
Filing date: 2003-09-24
Publication date: 2005-03-03
Also published as: PT1403746E; EP1403746A3; EP1403746A2; US20060129348A1; US7328123B2; DE10245594A1; EP1403746B1; ES2402292T3

Abstract

Monitoring method for a drive system with a motor and a moving part driven by the motor with the following steps: measurement of at least one drive-side motion quantity of the motor, measurement of at least one driven-side motion quantity of the moving part, and determination of an error signal as a function of the motion quantity measured on the drive side of the motor and the motion quantity measured on the driven side of the moving part.

Description

The invention concerns a monitoring method for a drive system with a motor and a moving part driven by a motor according to the preamble of claim 1.
Such drive systems are used, e.g., in modern painting systems for painting vehicle chassis, in the form of multi-axis painting robots, which control an atomizer according to a program in order to achieve optimum painting results.
Here, a collision of the painting robot with room boundaries, obstacles, or persons must be recognized in time in order to prevent damage to the painting robot or injury to the persons by the painting robot.
WO98/51453 discloses a monitoring method for a robot that enables collision recognition. Here, the reaction of the mechanism to the drive of the robot is evaluated and an error signal is generated as a function of this reaction.
For example, if the robot bumps against a stationary obstacle like a building wall, then a disturbance force acts on the robot. This force is fed back to the drive so that the drive is halted. For a collision with an elastic obstacle, a disturbance force likewise acts on the robot. Here, however, the force merely leads to a braking of the robot motion. However, in each case, the motion quantities of the drive, such as the angular position and the rpm of the motor shaft, deviate at least for a short time from the disturbance-free values.
Thus, the known monitoring method measures the drive-side motion quantities, such as the angular position and rpm of the motor shaft, on the robot to be monitored. The error signal for the collision recognition is then calculated from the motion quantities measured on the drive side and the preset regulation or control quantities for controlling the drive and the mechanism. The dynamic model takes into account, e.g., the mechanical inertia of the drive and the driven mechanism, as well as the elasticity of the mechanical coupling between the drive and the mechanism.
However, a disadvantage of this known monitoring method for collision recognition is the fact that the mechanical reaction of a collision-specific disturbance force from the mechanism on the drive is strongly reduced by interposed gears. For example, for painting robots, gears with a transmission ratio of 1:100 are used between the drive and the mechanism so that the mechanical reaction on the drive can be measured only with difficulty.
Another disadvantage of the known monitoring method is that incorrect models for the drive lead to large errors, because the reaction of the mechanism to the drive is then set incorrectly.
Finally, another disadvantage of the known monitoring method is also the fact that the angular position is measured on the drive side, while the acceleration is calculated by differentiating the measured value twice. This second derivative of the measured value leads to a very noisy signal.
Thus, the invention is based on the problem of improving the previously described, known monitoring method for collision recognition so that collision recognition is possible with higher reliability and a quicker reaction time even with interposed gears for as little measurement expense as possible.
Starting with the initially described, known monitoring method according to the preamble of claim 1, the problem is solved by the characterizing features of claim 1.
For determining the error signal, the invention includes the general technical teaching of not only measuring drive-side motion quantities of the drive system, but also motion quantities on the driven side, i.e., on the driven mechanism.
One advantage of measuring motion quantities on the driven side is the fact that the determination of the error signal is less inaccurate due to interposed gears. Thus, the monitoring method for collision recognition according to the invention can also be used for drive systems which have gears with a high transmission factor.
Another advantage of the monitoring method according to the invention is the fact that feedback of control or regulation quantities is not required, so that the monitoring method according to the invention is independent of the type and structure of the drive regulation or control.
According to the invention, an error signal that enables collision recognition is calculated from the motion quantities of the driven mechanism measured on the driven side and from the motion quantities measured on the drive side.
In a preferred embodiment of the invention, a comparison value for the drive force and the drive moment of the motor is calculated from the motion quantities measured on the driven side and from the motion quantities measured on the drive side, where preferably a dynamic model of the drive system and the mechanism, respectively, is taken into account. The dynamic model simulates, e.g., the inertia, the elastic components, and also the frictional forces or moments of the drive system and the mechanism, respectively. For disturbance-free operation of the drive system, the two comparison values must agree, while a deviation between the two comparison values can indicate a disturbance or even a collision.
The calculation of comparison values for the drive force or the drive moment can be implemented on the drive side and/or on the driven side by a recursive computational method, such as that described, e.g., in Roy Featherstone: “Robot Dynamics Algorithms,” Chapter 4 (Kluwer Academic Publishers, 1987).
The motion quantities measured on the drive side preferably involve the position, the velocity, and/or the acceleration of the motor. Here, it is sufficient to measure only one of these motion quantities, while the other two motion quantities can be determined through time differentiation or integration of the measured motion quantity. For example, it is possible to measure only the rotational velocity of the motor shaft, wherein the acceleration of the motor shaft is obtained through differentiation of the measured rotational velocity, and the angular position of the motor shaft can be calculated through integration of the measured rotational velocity.
For example, among other things, the acceleration of the motor can be measured as a drive-side motion quantity. Such a direct measurement of acceleration provides higher accuracy compared with differentiating the measured velocity or even the measured position. For example, differentiating the measured angular position of the motor shaft twice leads to a very noisy signal.
In contrast, the position, the velocity, and/or the acceleration of the driven mechanism can be measured as the driven-side motion quantities. Here, fundamentally, it is also sufficient to measure only one of these motion quantities, while the other two motion quantities can be obtained through time differentiation or integration of the measured motion quantity. For example, it is possible to measure only the velocity of the mechanism, wherein the acceleration of the mechanism is obtained through differentiation of the measured velocity and the position of the mechanism can be calculated through integration of the measured velocity.
However, preferably the acceleration of the mechanism is measured, among other things, as a driven-side motion quantity. Such a direct measurement of the acceleration provides higher accuracy compared with an acceleration value derived from differentiating the measured velocity or even the measured position. For example, differentiating the measured position of the mechanism twice leads to a very noisy signal.
For a multi-axis drive system, the error signal can preferably be determined separately for the individual axes of the drive system. The error signal for the individual axes can each form components of an error vector. For the evaluation, a scalar error value is then preferably calculated in order to also be able to recognize collisions, which effect only certain axes of the drive system.
In addition, the two comparison values for the drive force or the drive moment are also determined separately for each axis. However, due to the interaction between the individual axes, the motion quantities measured for the other axes are also taken into account for the calculation of the comparison values in the individual axis.
For suppressing temporary measurement errors, a sliding mean value of the error signal is preferably formed. The mean value determined in this way is then preferably compared with a predetermined threshold. If the threshold is exceeded, it is then assumed that a collision has occurred.
In addition, the monitoring method according to the invention also enables recognition of creeping disruptions of the drive system, such as, when the friction of the drive system increases due to bearing damage. For this purpose, preferably a sliding mean value of the error signal is formed over a long time period. The mean value formed in this way is then compared with a predetermined threshold. If the threshold is exceeded, it is then assumed that bearing damage has occurred, which can be indicated by a warning message.
Other advantageous refinements of the invention are characterized in the subordinate claims or are explained in more detail in the following together with the description of the preferred embodiment of the invention with reference to the figures. Shown are:
FIG. 1 a physical equivalent circuit diagram of an electromotor with a gear and a pivoting mechanism,
FIG. 2 a regulation-specific equivalent circuit diagram of an electromotor and a pivoting mechanism of a robot,
FIG. 3 a monitoring device according to the invention.
The physical equivalent circuit diagram in FIG. 1 shows a conventional electromechanical drive system for driving a shaft 1 of a painting robot, with additional drive systems being provided for driving the other shafts of the painting robot, which are configured similarly and thus are not described for simplification.
The shaft 1 of the painting robot is simulated in the physical equivalent circuit diagram by a mass m and a spring element c, while the damping of the shaft 1 is ignored for this embodiment.
The drive of the shaft 1 is here realized by an externally excited direct-current motor, which is represented in the physical equivalent circuit diagram as a series circuit composed of the ohmic resistor R of the armature, the inductance L of the armature, and the voltage u_iinduced by the rotor 2. In complex notation, the armature voltage u_Ais:
u _A =R·i _A +s·L·i _A +u _i (1)
The direct-current motor is connected over a drive shaft 3 and a gear 4 to the shaft 1, with the gear 4 converting the rotational motion of the drive shaft 3 into a different rotational motion.
The voltage u_iinduced in the armature circuit then results from the motor constant K_Mand the angular velocity ? _Aof the drive shaft 3 according to the following equation:
u _i =K _M·ω_A (2)
Furthermore, the drive moment M_Aof the direct-current motor is the product of the armature current i_Aand the motor constant K_M:
M _A =K _M ·i _A (3)
On the other side, a frictional force F_RVacts on the shaft 1. This force is converted by the gear 4 into a frictional moment M_RV: $\begin{matrix} M_{RV} = \frac{F_{RV}}{i_{G}} = \frac{v_{A} \cdot d_{G}}{i_{G}} = ω_{A} \cdot d_{G} & (4) \end{matrix}$
In addition, a load F_Lalso acts on the shaft 1. This load is converted by the gear 4 into a load moment: $M_{L} = \frac{F_{L}}{i_{G}} = \frac{c \cdot (x_{A} - x_{m}) + d_{G} \cdot (v_{A} - v_{m})}{i_{G}}$
The drive shaft 3 is thus accelerated by the drive moment M_Aand braked by the frictional moment M_RVand also by the load moment M_L. Taking into account the inertial moment J_Aof the drive, the following acceleration d? _A/dt of the drive shaft 3 then results: $\begin{matrix} \frac{ⅆ ω}{ⅆ t} = \frac{M_{A} - M_{L} - M_{RV}}{J_{A}} & (5) \end{matrix}$
In contrast, the block circuit diagram in FIG. 2 shows a regulation-specific equivalent circuit diagram of the direct-current motor and a mechanism 5, with the mechanism 5 being composed of the shaft 1 and the gear 4.
The calculation of the individual electrical and mechanical quantities is realized corresponding to the previously listed equations, as can be seen directly from FIG. 2.
However, the previously listed equations apply only to the case of undisturbed movement of the shaft 1. In contrast, if the motion of the shaft 1 is disturbed, then additional forces that lead to deviations of the actual system behavior from the ideal model behavior act on the shaft 1, in addition to the frictional force F_RVand the load F_L.
For example, if a painting robot bumps against the wall of a painting cabin, then the motion of the painting robot is strongly braked. Also, if there is bearing damage, the painting robot does not follow the modeled behavior exactly because the friction due to the bearing damage is strongly increased and is not taken into account in the previously listed equations. In such cases, the error should be recognized as quickly as possible in order to be able to introduce countermeasures.
Therefore, a monitoring device 6 is provided for each shaft of the painting robot. These monitoring devices recognize deviation of the actual behavior of the drive system from the modeled behavior. Here, for simplification, only the monitoring device 6 for the first shaft is shown, but the monitoring devices for the other shafts are configured identically.
The monitoring device 6 is connected on the input side to several sensors 7.1-7.4, with the sensors 7.1 and 7.2 measuring the angular velocity ? _A1and the angular position f _A1of the drive shaft 3, respectively, while the sensors 7.3 and 7.4 detect the position x_mof the shaft 1 and the acceleration a_mof the shaft 1, respectively.
Alternatively, it is also possible to provide only one sensor for measuring one drive-side motion quantity and one sensor for measuring one driven-side motion quantity, where additional motion quantities can be determined from the measured values. This can be implemented, e.g., through time differentiation or integration of the measured values or through the use of a so-called observer.
The position x_m1of the shaft 1 is then supplied to a differentiator 8, which calculates the velocity v_m1of the shaft 1 as a time derivative of the position x_m1, so that a measurement of the velocity v_m1in this embodiment is not required.
The position x_m1, the velocity v_m1, and the acceleration a_m1of the shaft 1 are then supplied to a computational unit 9, which calculates a model-based value F_MODELL,1for the force acting on the shaft 1 based on a predetermined model and also taking into account the corresponding motion quantities x_mi, v_mi, and a_miof the other shafts. Thus, the calculation of the model-based value F_MODELL,1is here implemented using load-side measurement data.
In addition, the monitoring device 6 calculates from drive-side measurement data a comparison value F_L1for the force acting on the shaft 1. For this purpose, the monitoring device 6 has two computational units 10, 11, which convert the measured angular velocity ? _A1and the measured angular position f _A1of the drive shaft 3 into corresponding values v_A1and X_A1while taking into account the gear transmission ratio i_G.
The drive-side calculated position path x_A1is then supplied to a subtractor 12, which calculates the difference ? x=x_A1−x_m1between the drive-side calculated position path X_A1and the actually measured position x_m1of the mass m of the shaft 1. This difference ? x is supplied to another computational unit 13, which calculates the elastic percentage ? x·c of the force acting on the shaft 1 while taking into account the spring constant c.
In contrast, the drive-side calculated position velocity v_Alis supplied to a subtractor 14, which calculates the difference ? v=V_A1−V_m1between the drive-side calculated position velocity V_A1and the actually measured velocity of the mass m of the shaft 1. This difference ?v is then supplied to a computational unit 15, which calculates the percentage of force acting on the shaft 1 due to the gear damping as a product of the damping constant d_Gand the velocity difference ? v.
On the output side, the two computational units 13, 15 are connected to an adder 16, which calculates the comparison value F_L1for the force acting on the shaft 1 from the elastic percentage c·? x and the damping percentage d_G·? v.
Furthermore, the monitoring device 6 has a subtractor 17, which is connected on the input side to the adder 16 and the computational unit 9, and calculates the difference between the two comparison values F_L1and F_MODELL,1, and outputs an error signal F_STÖR,1.
For undisturbed motion of the shaft 1, the two comparison values F_L1and F_MODELL,1agree up to an unavoidable measurement error, because the modeling of the dynamic behavior of the shaft 1 reproduces its actual behavior. The calculation of the force F_L1acting on the shaft 1 from the motion quantities measured on the drive side, ? _A1and f _A1, then produces the same value as the calculation of the force F_MODELL,1acting on the shaft 1 from the motion quantities X_M1and a_M1measured on the load side.
In contrast, if the motion of the shaft 1 is disturbed, then the comparison values F_L1and F_MODELL,1deviate from each other, with the deviation of these quantities reproducing the severity of the disturbance. Thus, increased bearing friction leads only to a relatively small error signal F_STÖR,1, while the collision of the shaft 1 with a boundary leads to a very large error signal F_STÖR,1.
Furthermore, for evaluating the operating behavior for all of the shafts, there is an evaluation unit 18, which is connected on the input side to the individual monitoring devices 6 for the individual shafts and receives the error signals F_STÖR,ifor all of the shafts.
The evaluation unit 18 contains a support element 19, which receives the error signals F_STÖR,ifor all of the shafts in parallel and outputs them as a multi-dimensional disturbance force vector F_STÖRto a computational unit 20.
The computational unit 20 then calculates from the individual components of the disturbance force vector F_STÖRa scalar error value F, which reproduces the severity of the disturbance acting on the painting robot.
The error value F of the disturbance force vector F_STÖRis then supplied to a computational unit 21, which calculates the sliding mean value of the error signal F in order to suppress the influence of measurement outliers in the evaluation. The averaging period of the computational unit 21 is relatively short, so that suddenly occurring disturbances, such as a collision of the painting robot with an obstacle, are recognized quickly.
On the output side, the computational unit 21 is connected to a threshold element 22. An emergency-off signal is generated when a predetermined threshold is exceeded, which leads to immediate halting of the painting robot in order to prevent damage to the painting robot and to the surroundings or even injuries to persons in the area.
In addition, the evaluation unit 18 has another branch in order to be able to react to more slowly occurring and smaller disturbances. For this purpose, the computational unit 20 is connected to a computational unit 23, which calculates the sliding mean value of the error signal F, where the computational unit 23 has a greater averaging period than the computational unit 21, so that only changes that take place over a longer time period are taken into account.
On the output side, the computational unit 23 is connected to a threshold element 24, which generates a warning signal when a predetermined threshold is exceeded.
The invention is not limited to the previously described embodiment. Indeed, a plurality of variants and modifications are possible, which likewise make use of the concept of the invention and thus fall within the scope of protection.

Claims

1. A method for monitoring a drive system of a robot, more specifically a painting robot, with a motor and a moving part driven by the motor, with the following steps:

measuring at least one drive-side motion quantity of the motor;

measuring at least one driven-side motion quantity of the moving part; and

determining an error signal as a function of the motion quantities of the motor measured on the drive side and of the motion quantities of the moving part measured on the driven side.

2. The method according to claim 1 wherein the determining step is further comprises the following steps:

calculating a first comparison value for one of a drive force and a drive moment of the motor with reference to the motion quantity of the motor measured on the drive side;

calculating a second comparison value for one of a drive force and a drive moment of the motor with reference to the quantity of the moving part measured on the driven side;

comparing the first comparison value with the second comparison value; and

selectively generating the error signal in response to the comparing step.

3. The method according to claim 2 wherein the drive-side motion quantity measuring step is further defined by the velocity of the motor is measured and the first comparison value is calculated with reference to the measured velocity.

4. The method according to claim 2 wherein the drive-side motion quantity measuring step is further defined by the position of the motor is measured and the first comparison value is calculated with reference to the measured position of the motor.

5. The method according to claim 2 wherein the driven-side motion quantity measuring step is further defined by one of the position, the velocity, and the acceleration of the moving part is measured and the second comparison value is calculated for one of the drive force and the drive moment of the motor with reference to the one of the measured position, the measured velocity, and the measured acceleration of the moving part.

6. The method according to claim 2 wherein the second value calculating step is further defined by the second comparison value is calculated by a recursive computational method from one of the measured position, the measured velocity, and the measured acceleration of the moving part.

7. The method according to claim 2 wherein the drive system has a plurality of moving shafts, with one of the position, the velocity, and the acceleration being measured for the individual shafts, with the second comparison value being calculated separately for the individual shafts.

8. (Cancelled)

9. The method according to claim 7, wherein the second value calculating step is further defined by the second comparison value being calculated as a function of one of the positions, the velocities, and the accelerations of the plurality of shafts.

10. The method according to claim 7 wherein the error generating step is further defined by the error signal is generated separately for each shaft of the drive system.

11. The method according to claim 2 further comprising the step of: determining a sliding mean value of the error signal.

12. A method for monitoring a drive system of a robot having a motor and a member moved by the motor, comprising the steps of:

generating a force with the motor to move the member;

communicating at least part of the moving force generated by the motor to the member with a drive shaft;

sensing at least one motion quantity of the drive shaft with a first sensor during the communicating step; and

sensing at least one motion quantity of the member with a second sensor during the communicating step.

13. The method of claim 12 further comprising the steps of:

determining a first force communicated by the drive shaft to the member in response to the sensed motion quantity of the drive shaft; and

determining a second force acting on the member in response to the sensed motion quantity of the member.

14. The method of claim 13 further comprising the step of:

comparing the determined first and second forces.

15. The method of claim 14 further comprising the step of:

stopping the motor in response to the comparing step.

16. The method of claim 15 wherein the stopping step is further defined by:

stopping the motor at a rate corresponding to a degree of difference between the first and second signals.

17. The method of claim 14 wherein the communicating step is further defined by:

communicating the moving force to the member and at least one other member with the drive shaft.

18. The method of claim 17 further comprising the steps of:

sensing at least one motion quantity of the other member with a third sensor during the communicating step; and

determining a third force acting on the other member in response to the sensed motion quantity of the other member.

19. The method of claim 18 wherein the comparing step is further defined by:

comparing the determined first, second and third forces.

20. The method of claim 19 wherein the comparing step is further defined by:

comparing a sum of the second and third forces with the first force.