Controller for painting robots

Abstract

A robot controller (112, 114, 631, 632) is adapted to execute a program (610), the program (610) comprising an indication of a setpoint speed of a robot arm (120), an indication of a simultaneous setpoint fluid flow rate per unit time of a spray gun (122) supported by the robot arm, and an indication of a number of simultaneous further setpoints for the spray gun. The robot controller is configured to: obtain an estimate of an actual speed of the robot arm; determine whether the estimate deviates from the setpoint speed; and, in the event of a deviation, adjust the setpoint fluid flow rate per unit time according to a first compensation function. In an embodiment, the robot controller is further configured to, in the event of a deviation, concurrently adjust the number of further setpoints according to a second compensation function different from the first compensation function.

Description

Technical Field

[0001] The present disclosure relates to the field of robot control, and in particular to a robot controller for a robot manipulator for operating a spray gun. Background Art

[0002] With the long-term use of spraying robots, the problem of controlling the robot to operate the spray gun has been solved in many ways.

[0003] US 3,525,382 discloses a system which is controlled in an open loop manner by a program which specifies the tool speed and the flow of coating material from the tool.

[0004] EP0145991 discloses a robot-borne spraying device associated with a measuring device for determining the translational speed of the spraying device and a flow control device for controlling the fluid flow rate as a function of the translational speed. This aims to achieve a constant amount of fluid delivered per unit length of the workpiece.

[0005] US5373221 discloses a system for simulating a robot executing a programmed trajectory. The simulation takes into account predefined fillet distances and similar parameters that may cause the actual trajectory to deviate from the programmed trajectory. The simulated speed, rather than the speed according to the programmed trajectory, can be used to control the sealant flow rate from a sealant dispenser carried by the robot.

[0006] In US5290266, the command signal controlling the sealant flow rate from the sealing gun unit is determined by the command movement speed of the sealing gun movement. A pre-taught program directly or indirectly defines the command movement speed, and the sealant flow rate is dynamically calculated by the command movement speed to achieve a constant amount of sealant per unit length.

[0007] US4922852 discloses a robot having a controller programmed to direct a nozzle over a workpiece surface to dispense a bead of fluid thereon. The operation is directed based on variables including a set point representing a desired total volume of fluid to be applied to a single workpiece. Furthermore, it is disclosed that the amount of fluid dispensed per unit distance can be controlled, i.e., taking into account a tool speed signal emitted from the robot controller representing the nozzle speed relative to the workpiece.

[0008] An important class of industrial spray robot controllers are programmed with respect to a set point spray gun speed and a set point fluid flow rate per unit time. This is because, unlike a simple dispenser, a spray gun is additionally configurable with respect to a number of other set point values, which may include settings related to atomization, electrostatic charging, and various air flow rates per unit time, which may be adjusted to modify the spray plume shape for a given nozzle and spray type. Simulation software exists for predicting the spray thickness produced by a given combination of set point speed, fluid flow rate, air flow rate, etc., but it is considered relatively inaccurate by some participants, who prefer to run preliminary spray tests to verify thickness before initiating commercial operations.

[0009] The basic problem of the present disclosure is the automatic control of a spraying robot programmed according to a set-point spray gun speed and a set-point fluid flow rate per unit time. Summary of the invention

[0010] One object is to provide a robot controller for executing a program having a set point speed of a robot arm and an indication of a set point fluid flow rate per unit time of a spray gun supported by the robot arm. Another object is to provide such a robot controller having the ability to adapt the execution of the program to fluctuations in the actual speed of the robot arm. A further object is to provide a method for controlling a robot arm and a spray gun according to a program having a set point speed of the robot arm and an indication of a set point fluid flow rate per unit time of the spray gun.

[0011] These and other objects are achieved by the present invention, as defined by the attached independent claims.The dependent claims are directed to embodiments of the invention.

[0012] A first aspect of the invention relates to a robotic controller adapted to execute a program comprising an indication of a setpoint speed of a robotic arm, an indication of a simultaneous setpoint fluid flow rate per unit time of a spray gun supported by the robotic arm, and an indication of a number of simultaneous further setpoints of the spray gun. The robotic controller is configured to: obtain an estimate of an actual speed of the robotic arm; determine whether the estimate deviates from the setpoint speed; and, in the event of a deviation, adjust the setpoint fluid flow rate per unit time according to a first compensation function.

[0013] By controlling the spray gun based on a set point fluid flow rate adjusted per unit time (for example, if the actual speed of the robot arm is found to be lower than the set point speed, the flow rate is reduced) rather than a set point fluid flow rate per unit time, the present invention helps to maintain the final result of spraying close to the programmer's intention, especially with regard to the expected thickness of the sprayed fluid. Assuming that the actual speed drops from the set point speed during program execution, the present invention can prevent the local formation of an overly thick layer. In the special case of spraying, excessive thickness may cause the coating to peel off or prematurely age. In addition, the present invention can avoid the wasteful use of spray fluid. In this way, in applications where the spray fluid is distributed in each batch of pre-filled barrels, the liquid level does not need to include sufficient margin to take into account potential waste. Under the condition that the actual speed exceeds the set point speed, the present invention ultimately ensures the integrity and reliability of the coating at all points of the workpiece.

[0014] The invention also provides a stable and well-conditioned automatic control. More precisely, since the setpoint fluid flow is used (without adjustment) unless a deviation of the actual speed from the setpoint speed is determined, the constant availability of a speed estimate is not critical for the performance of the control. Thus, the robotic controller according to the invention can be said to adaptively alternate between open-loop control of the spray gun (when an estimate of the actual speed does not deviate from the setpoint speed or an estimate is not available) and closed-loop control (when a deviation is determined) of the spray gun. Furthermore, as mentioned above, the dependence of the thickness on speed and other factors may be known only locally near the operating point (e.g. as an elasticity), so that calculating the setpoint speed forward by the thickness may be much more difficult than finding a suitable incremental adjustment.

[0015] As used herein, a quantity "indicated" in a program or script refers to a value typed in by an operator or programmer in an unambiguous human or machine-readable form. Although additional quantities may be implied from the program and may be derived from the program based on calculations and known relationships to the quantities indicated in the program, the intended meaning of "indicated" does not cover such implied quantities.

[0016] Further, two set-point quantities are "simultaneous" within the meaning of the claims if the robotic controller observes or executes them during coincident or overlapping time periods. For example, if a program instructs the robotic controller to move a robotic arm over a portion of a workpiece at a set-point velocity v* while causing a spray gun to apply dq* / dt units of fluid and dp* / dt units of air per unit time, then v*, dq* / dt, and dp* / dt are simultaneous set-point quantities. A common way to program a spray robot is to have the robotic arm move over a workpiece along a path at a constant velocity so that the spray plume visits all points on each surface to be sprayed; therefore, the robotic arm can typically be configured to have a piecewise constant set-point velocity over a corresponding time period.

[0017] The "compensation function" is an at least partially valid theoretical or empirical relationship between the actual robot arm velocity v and at least one quantity x that affects the thickness h of the sprayed liquid (e.g., fluid flow per unit time, air flow per unit time). The compensation function may be an expression R of the form R(v,x)=h. The compensation function may be expressed as an implicit function When the speed v is near the set point speed v*, When the velocity has been determined to be off, the robot controller can evaluate the implicit function for the estimated actual velocity v The adjusted set point value of x is fed to the spray gun. The expression R, implicit function Etc. may be represented analytically as an empirical fit curve, a table of values, an artificial neural network trained on representative examples, or any other suitable machine-readable form.

[0018] As used herein, the term "spray gun" covers all products known in the art, such as atomizer guns, atomizer bells, spray bells, rotary bell atomizers, bell applicators, and spray applicators. In this sense, a spray gun can be suitable for applying a fluid, such as spraying. There are also spray guns for applying free-flowing dry powders in powder coating applications, where the powder acts as a solvent-free spray and is therefore equivalent to a spray fluid.

[0019] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless otherwise explicitly defined herein. Unless otherwise explicitly stated, all references to "element, device, component, part, step, etc." are to be interpreted as referring to at least one instance of the element, device, component, part, step, etc. Unless explicitly stated otherwise, the steps of any method disclosed herein do not have to be performed in the exact order disclosed.

[0020] In one embodiment, the robot controller is further configured to take compensating measures related to further setpoint quantities (e.g. atomization, air flow per unit time, spray plume geometry, electrostatic charging) in the event of a determined speed deviation. In practice, the robot controller can be configured to adjust the further setpoint quantities according to a second compensation function different from the first compensation function concurrently with the adjustment of the setpoint fluid flow per unit time. Since the second compensation function is defined independently of the first compensation function and is typically different from the first compensation function since it involves different quantities, this embodiment makes it possible to adjust each setpoint value in an appropriate manner in the event of a speed deviation. This facilitates obtaining an attractive end result with a high degree of uniformity within a batch of workpieces and between different batches.

[0021] In a second aspect, the invention provides a method of controlling a robot arm and a spray gun supported by the robot arm. The method comprises: obtaining a program including an indication of a set point speed of the robot arm, and an indication of a further simultaneous set point fluid flow rate per unit time of the spray gun, and an indication of a further simultaneous set point number of the spray gun; obtaining an estimate of an actual speed of the robot arm; determining whether the estimate deviates from the set point speed; and in the event of a deviation, adjusting the set point fluid flow rate per unit time according to a first compensation function.

[0022] Another aspect of the invention relates to a computer program comprising instructions for causing a computer or in particular a robot controller to perform the above method. The computer program may be stored or distributed on a data carrier. As used herein, a "data carrier" may be a transient data carrier (such as a modulated electromagnetic wave or light wave) or a non-transient data carrier. Non-transient data carriers include volatile and non-volatile memories, such as permanent and non-permanent storage devices of magnetic, optical or solid-state type. Still within the scope of a "data carrier", such a memory may be fixedly mounted or portable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Various aspects and embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0024] Figure 1 An industrial spray coating system is shown, which includes a robotic arm equipped with a spray gun, a robotic controller configured according to an embodiment of the present invention, and a conveyor device for bringing workpieces into and out of the operating area of ​​the robotic arm;

[0025] Figure 2 is a flow chart of a method according to an embodiment of the invention;

[0026] Figures 3 to 5 is a graph of various compensation functions for embodiments of the present invention; and

[0027] Figure 6 An example architecture of a cooperative control algorithm suitable for controlling a robotic arm and an attached spray gun is shown. DETAILED DESCRIPTION

[0028] Various aspects of the present disclosure will now be described more fully below with reference to the accompanying drawings, in which certain embodiments of the invention are shown. However, these aspects can be implemented in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that the present disclosure will be thorough and complete and fully convey the scope of all aspects of the invention to those skilled in the art. The same numbers refer to the same elements throughout the description.

[0029] Figure 1 An industrial spray system 100 is shown, which generally includes a robotic arm 120, a robotic controller 110, and a conveyor device 140. The robotic arm 120 includes a plurality of segments joined by a rotatable or linear joint extending from a base 128 and supporting a spray gun 122 at its outer end, the spray gun 122 being adapted to spray a fluid through a nozzle 124 onto a surface of a stationary or moving workpiece 130 on the conveyor device 140. The robotic arm 120 may include (not shown) supply lines for feeding spray fluid, air, gas, etc., to the spray gun 122, return lines for collecting excess fluid, etc., and wiring harnesses for supplying power and control signals. In order to allow the spray gun 122 to reach various surfaces of the workpiece 130 and effectively cover these surfaces, the robotic arm 120 may be moved by translation and / or rotation, and the spray gun 122 itself may be rotated relative to the robotic arm 120. The velocity of the robotic arm 120 during such movement may be measured or estimated with reference to a tool center point (TCP) 126. Set point speed may also be referred to as TCP 126 .

[0030] Figure 1 The lower part of the figure shows an example structure of the robot controller 110, which includes a motion control system 112, a process control system 114, a memory 116 suitable for storing executable software (including various programs, such as spray programs with indications of set point numbers), and a user interface 118 configured to display various aspects of the current conditions of the spray system 100 and accept commands entered by an operator. Programs can be prepared or uploaded directly to the memory 116 using the user interface 118. The motion control system 112 is mainly responsible for feeding motion control signals to the actuators directed therein to the robot arm 120, and monitoring the robot arm 120 through rotational position sensors, torque / strain / pressure sensors, etc. The process control system 114 is mainly responsible for controlling various aspects of the spray gun 122, such as atomization, electrostatic charging, various air flows that modify the shape of the spray plume, cleaning and replacement of the nozzle.

[0031] In some embodiments, the motion control system 112 and the process control system 114 operate independently of each other, except that the control system 114 may execute set point quantities that have been adjusted based on an estimate of the actual speed sent from the motion control system 112. The mutual independence of the two systems 112, 114 can be achieved by having them execute as different threads in a shared processing resource and / or on separate processing resources of the robotic controller 110. Such a structure of the robotic controller 110 can facilitate stable operation of the spray system 100 and the ability to quickly respond to fluctuations in speed or other quantities.

[0032] The method 200 for controlling the robotic arm 120 and attaching the spray gun 122 is visualized as Figure 2The method also represents an example manner of operating the robot controller 110.

[0033] The method 200 refers to a program obtained in a first step 210 of the method 200, which program includes an indication of a setpoint velocity v* of the robot arm 120, and an indication of a simultaneous further setpoint fluid flow rate dq* / dt per unit time of the spray gun 122, and an indication of a simultaneous further setpoint quantity x* of the spray gun. The tuple (v*, dq* / dt, x*) of values ​​of the instantaneous setpoint quantity may be associated with a surface of the workpiece 130. When the workpiece 130 is a vehicle, the surface may be a roof, a ceiling, a door, a fender, etc.

[0034] In a second step 220 of the method 200, an estimate v of the actual speed of the robot arm 120 is obtained while the robot arm 120 and the spray gun 122 are processing the surface of the workpiece 130, for which the tuple of values ​​of the number of setpoints is valid at the same time. The estimate v can be derived from one or more robot arm motion control signals u1 generated by the motion control system 112, without relying on the sensed instantaneous speed of the robot arm 120. Alternatively, the estimate v is the reading of a sensor (not shown) mounted on or at the robot arm 120. The sensor can be an inertial sensor or an optical sensor. If the speed of the robot arm 120 relative to the workpiece 130 is of interest, it may be preferred to use an optical sensor; the relative speed can be determined by tracking visual features on the surface of the workpiece 130, calculating optical flow and similar techniques. Further alternatively, the estimate can be derived from one or more sensor signals from one or more rotational position sensors, which are attached to or associated with corresponding actuators in the robot arm 120. The rotational position sensor can be implemented as a resolver or a rotary encoder, from which speed information can be calculated.

[0035] In a third step 230, it is determined whether the estimate v deviates from the set point speed v*. If the robot is operating close to its axis speed or torque limits, the speed may temporarily drop. Additionally, the conveyor device 140 may move the workpiece 130 to an inconvenient area where the robot arm 120 is operating close to its motion limits. From the perspective of the robot controller 110, the speed deviation may correspond to a condition of the form |vv*|≥ε that satisfies a predetermined constant ε>0 representing a tolerance. The tolerance may be set with consideration of how much thickness deviation in the final result is considered acceptable, but the tolerance may also reflect the expected amount of noise in the speed estimate of the robot arm 120. If this condition is met, the third step 230 returns a positive decision (Y branch) and execution of the method 200 proceeds to the fourth step 240. Conversely, if |vv*|<ε or the estimate v is not available at this time, it is determined that there is no deviation (N branch); for this result, execution of the method 200 may continue in the second step 220, possibly after a suitable delay has expired so that it makes sense to update the estimate of the speed of the robot arm 120.

[0036] In a fourth step 240, the set point fluid flow rate per unit time is adjusted according to the first compensation function, i.e., by means of which the value dq* / dt is adjusted according to the indication in the program to an adjustment value, expressed as In addition, there is an optional adjustment of the number of further setpoints x* of the spray gun at the same time according to the second compensation function, the adjustment result is expressed as Then, for the remaining duration of the treatment of said surface of the workpiece 130, the adjustment value of the number of setpoints and can be fed to the spray gun 122. Alternatively, and obviously depending on the total extent of the surface, it may be sensible to update the velocity estimate v of the robot arm 120 so that the setpoint number and The adjustment value of can be updated. In the case of |vv*|<ε, the robot controller 110 can potentially resume using the set point quantity according to the instructions in the program; if the fourth step 240 is terminated as a result, the execution of the method 200 can continue from the second step 220, as described for the N branch of the third step 230.

[0037] The concept of compensation function has been introduced and Figure 3 , 4 and 5 are further illustrated.

[0038] Figure 3Three compensation functions for the fluid flow rate dq / dt per unit time are shown, corresponding to 1, 2 and 3 units of thickness h. For different numbers of set points, different families of compensation functions can be applied. Each compensation function can be understood as a contour of a completely or incompletely known thickness function. It is sufficient to have local knowledge of the compensation function in the vicinity of the set point velocity v*. Using Figure 3 Possible solutions for the family of compensation functions shown are as follows:

[0039] 1. One of the compensation functions that most closely matches the setpoint quantities v*, dq* / dt is selected.

[0040] 2. The selected compensation function of the estimated actual speed v is evaluated to produce the adjusted set point value

[0041] 3. Adjusted setting value Applied to spray guns.

[0042] The determined speed deviation can trigger the adjustment of one or more set point quantities. For a given set point quantity, different compensation functions can be applied depending on whether the set point quantity is adjusted alone or in combination with other set point quantities. To illustrate this difference, if the air flow rate per unit time dp / dt is adjusted in combination with the fluid flow rate per unit time dq / dt, then Figure 4A is a graph of the family of compensation functions to be used. In contrast, if the air flow per unit time dp / dt is the only quantity to be adjusted in response to speed deviations, then Figure 4B The compensation function in should be used. Figure 4A and 4B As can be seen from the comparison, Figure 4B A slightly steeper slope in corresponds to a relatively stronger response.

[0043] Referring again to the fluid flow rate per unit time dq / dt, Figure 5 An alternative representation of the compensation function for a thickness value h=h0 is depicted. Figure 5A hashed region is shown surrounded by an upper limit 501 and a lower limit 502, which define a permissible range of fluid flow rate per unit time for each value of speed v around a setpoint speed v*. Note that the spacing of the boundaries 501, 502 is non-constant with respect to speed v, reflecting that in this example use case, for higher values, an imprecise control of the fluid flow rate dq / dt per unit time is somewhat more acceptable. The fact that for each speed value v, a range of fluid flow rate values ​​is permissible provides the robot controller 110 with some freedom as to whether small speed deviations should be considered negligible or should trigger an adjustment; in this example, such freedom exists for the fluid flow rate, but may not exist for other setpoint quantities.

[0044] As use Figures 3 to 5 As an alternative to compensation functions of the type illustrated, incremental compensation may be applied. More precisely, let s denote the distance traveled by TCP 126, from the chain rule:

[0045]

[0046] Recognize the differential relationship:

[0047]

[0048] holds true for small Δv. Here, dq* / ds may be understood as the set point fluid flow rate per unit distance traveled by the TCP 126 or equivalently the spray gun 122. Therefore, the adjusted set point fluid flow rate per unit time may be calculated as the set point flow rate per unit time indicated in the program, dq* / dt, with the addition of a correction term:

[0049]

[0050] Another conclusion drawn from this is that the slope of the first compensation function at the set point speed v* is proportional to a factor representing the desired fluid flow rate per unit length traveled by the spray gun 122 or TCP 126. This factor can be derived from the set point speed and the set point fluid flow rate per unit time indicated in the execution program.

[0051] Yet another alternative is to adjust the set point quantity based on a tabulated value.

[0052] The described architecture will now be described, wherein control algorithms suitable for controlling the robot arm and the attached spray gun cooperate. Figure 1 , the motion control system 112 is configured to generate one or more motion control signals u1 to be fed to the actuators in the robotic arm 120, and the process control system 114 ... based on the adjusted and unadjusted set point quantities. y*, To control the spray gun 122. These entities of the robot controller 110 operate based on a program 610 that contains instructions for a setpoint velocity v* and three setpoint quantities x*, y*, z*. By monitoring the robot arm 120 or the motion control signal u1 ( Figure 6 The previous option is depicted), the estimate v of the actual speed of the robot arm 120 is fed to a comparator 620 which is configured to determine whether it deviates from the set point speed v*. If this is the case, the comparator 620 issues an activation signal u2 directed to a first compensator 631 which is configured to output an adjustment value of the first set point quantity x* in active mode Furthermore, the activation signal u2 from the comparator 620 activates the second compensator 632, which is configured to output an adjustment value of the third setpoint quantity z* in the active mode. Adjustment values ​​of the first set point quantity and the third set point quantity is supplied to the process control system 114. Note that the motion control system 112 operates based on instructions in the program 610, but is independent of the process control system 114. The comparator 620 and compensators 631, 632 may be implemented as dedicated circuitry or by software instructions.

[0053] Aspects of the disclosure are mainly described above with reference to a few embodiments. However, as readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A robotic controller (110) adapted to execute a program, the program comprising an indication of a setpoint speed of a robotic arm (120), an indication of a simultaneous setpoint fluid flow rate per unit time of a spray gun (122) supported by the robotic arm, and an indication of a number of simultaneous further setpoints for the spray gun, wherein the robotic controller is configured to: Obtaining an estimate of the actual velocity of the robotic arm, wherein the estimate is derived from one or more of: a) one or more robot arm motion control signals generated by the robot controller independent of the sensed instantaneous velocity of the robot arm, b) one or more sensor signals from one or more rotational position sensors attached to one or more respective actuators, c) a sensor on or at the robot arm; determining whether the estimate deviates from the set point speed; as well as, In the event of a deviation, the set point fluid flow rate per unit time is adjusted according to a first compensation function. 2 . The robot controller according to claim 1 , wherein the robot controller is further configured to, in the event of a deviation, concurrently adjust the further number of set points according to a second compensation function that is different from the first compensation function.

3. A robotic controller according to claim 1 or 2, wherein the further setpoint quantity is a quantitative characteristic of one or more of the following: atomisation, air flow per unit time, spray plume geometry, electrostatic charging. 4 . The robot controller according to claim 1 , wherein the sensor on or at the robot arm is an inertial sensor and / or an optical sensor.

5. The robotic controller of claim 1 , wherein the slope of the first compensation function is proportional to a first factor representing a desired fluid flow rate per unit length traveled by the spray gun, wherein the robotic controller is configured to derive the first factor from an indicated set point speed and a set point fluid flow rate per unit time.

6. The robot controller according to claim 1 or 2, suitable for controlling the robot to spray a moving workpiece (130), wherein the actual speed of the robot arm is relative to the speed of the moving workpiece.

7. The robot controller according to claim 6, wherein: The moving workpiece (130) is an object moved by the conveyor device (140).

8. The robot controller according to claim 1 or 2, comprising: A motion control system (112) for controlling the robot arm; as well as a process control system (114) for controlling the spray gun, Wherein the motion control system operates independently of the process control system.

9. A method (200) of controlling a robot arm (120) and a spray gun (122) supported by the robot arm, the method comprising: obtaining (210) a program comprising an indication of a setpoint speed of the robot arm, and an indication of a simultaneous setpoint fluid flow rate per unit time of the spray gun, and an indication of a number of simultaneous further setpoints of the spray gun; Obtaining (220) an estimate of an actual velocity of the robot arm, wherein the estimate is derived from one or more of: a) one or more robot arm motion control signals generated by a robot controller independent of the sensed instantaneous velocity of said robot arm, b) one or more sensor signals from one or more rotational position sensors attached to one or more respective actuators, c) a sensor on or at the robot arm; determining (230) whether the estimate deviates from the setpoint speed; as well as In the event of a deviation, the set point fluid flow rate per unit time is adjusted (240) according to a first compensation function.

10. A computer program product comprising instructions for causing a robot controller (110) according to claim 1 to perform the steps of the method (200) according to claim 9.

11. A data carrier on which a computer program product according to claim 10 is stored.

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