EP-4739443-A1 - A PAINTING SYSTEM

EP4739443A1EP 4739443 A1EP4739443 A1EP 4739443A1EP-4739443-A1

Abstract

A painting system, comprising: a paint nozzle (110) configured to dispense paint onto a surface; an arm configured to move the paint nozzle over the surface in accordance with an image sweep pattern (310); pressurizing means operable to feed paint into a paint supply line which extends up to the paint nozzle; and a controller arranged to control the pressurizing means. The controller is configured with a control law that includes a feedback component for maintaining an output paint pressure of the paint supply line at a setpoint value and further includes a feedforward component which is dependent on image data in a region (320) of a user-defined image (300), which region is next to be printed according to the image sweep pattern.

Inventors

FINNESTAD, Yngve
TRYDAL, Jakob
MOSSIGE, Morten
SANDVIK, Bjarne

Assignees

ABB SCHWEIZ AG

Dates

Publication Date: 20260513
Application Date: 20230705

Claims (1)

CLAIMS 1. A painting system (100), comprising: a paint nozzle (110) configured to dispense paint onto a surface (170); an arm (111) configured to move the paint nozzle over the surface (170) in accordance with an image sweep pattern (310); pressurizing means (130) operable to feed paint into a paint supply line (120) which extends up to the paint nozzle (110); and a controller (140), which is arranged to control the pressurizing means and configured with a control law that includes a feedback component for maintaining an output paint pressure (^) of the paint supply line at a setpoint value (^ ∗ ), characterized in that the control law further comprises a feedforward component dependent on image data in a region (320) of a user-defined image (300), which region is next to be printed according to the image sweep pattern. 2. The painting system (100) of claim 1, wherein the feedforward component is dependent on a predicted paint consumption in the region (320) of the user-defined image. 3. The painting system (100) of claim 2, wherein the feedforward component provides a temporary increase of the feedback component if the predicted paint consumption in the region (320) exceeds an upper threshold. 4. The painting system (100) of claim 2, wherein the feedforward component provides a temporary decrease of the feedback component if the predicted paint consumption in the region (320) is less than a lower threshold. 5. The painting system (100) of any of the preceding claims, wherein the region (320) corresponds to a subset of the user-defined image (300) which is to be printed during the next ^ units of time, where ^ is predetermined. 6. The painting system (100) of any of claims 2 to 5, wherein the feedforward component is dependent on a rate of change of the predicted paint consumption with respect to time. 7. The painting system (100) of any of the preceding claims, wherein the controller (140) is arranged to control the pressurizing means (130) by applying a numeric control signal (^), which includes the feedback component and the feedforward component. 8. The painting system (100) of claim 7, wherein the feedforward component provides a temporary additive modification (^ ^ ) of the feedback component. 9. The painting system (100) of claim 7 or 8, wherein: the feedback component of the control signal (^) is locally related to a deviation of the output paint pressure (^) from the setpoint value (^ ∗ ) by a predetermined control gain (^ ^ ); and the feedforward component provides a temporary modification of the control gain. 10. The painting system (100) of any of claims 7 to 9, wherein: the controller (140) includes a proportional–integral, PI, regulator or a proportional– integral–derivative, PID, regulator arranged to generate the feedback component of the control signal (^); and the feedforward component provides a temporary modification of an integral term in the PI or PID regulator. 11. The painting system (100) of any of the preceding claims, wherein the pressurizing means (130) comprises at least one of: a pump, a compressor, a valve towards a pressurized reservoir. 12. A method of printing a user-defined image (300) onto a surface (170), comprising: dispensing paint from a paint nozzle (110) while the paint nozzle is moved over the surface (170) in accordance with an image sweep pattern (310); sensing an output paint pressure (^) of a paint supply line (120) which extends up to the paint nozzle; and feeding a flow of paint into the paint supply line (120) so as to maintain an output paint pressure (^) of the paint supply line at a setpoint value (^ ∗ ), characterized by determining, from image data in a region (320) of the user- defined image (300), which region is next to be printed according to the image sweep pattern, an adjustment to be applied to said flow of paint. 13. The method of claim 12, where the adjustment is determined on the basis of a predicted paint consumption in the region (320) of the user-defined image. 14. The method of claim 12 or 13, wherein the region (320) corresponds to a subset of the user-defined image (300) which is to be printed during the next ^ units of time, where ^ is predetermined. 15. A computer program comprising instructions to cause a controller (140) to execute the method of any of claims 12 to 14.

Description

A PAINTING SYSTEM TECHNICAL FIELD [0001] The present disclosure relates to the field of automated painting by means of a robot-carried paint nozzle. It proposes techniques for controlling a paint supply system in an automated painting system, and in particular for controlling pressurizing means in the paint supply system. BACKGROUND [0002] Figure 1A shows an automated painting system 100, in which a paint nozzle 110 is arranged on a movable robot arm 111. The paint nozzle 110 and robot arm 111 are controlled by a robot controller 180 to dispense paint onto a surface 170 in such manner as to form an image thereon. The paint nozzle 110 is supplied with paint from a paint tank 150 through a paint supply line 120. A further controller 140 is arranged to control a pressurizing means 130 so as to maintain an output paint pressure ^ of the paint supply line at a setpoint value ^∗. [0003] It is common practice in painting systems of this type to use a feedback loop for controlling the pressure of the paint supply line 120. For example, EP3912822A1 discloses an inkjet printing system where the pressure of the supply line to the inkjet nozzle is controlled in response to a feedback signal which indicates the pressure in the supply line, and which optionally indicates the pressure in a recirculation line. However, it has been observed that similar painting systems sometimes suffer from a slower than desirable control response. The slowness could at worst manifest itself in the form of visible transients (or image artefacts), such as too thin paint coverage in the beginning of a heavily painted image portion or occasional paint leakage after the painted portion ends. While it may be hypothesized that the slow response is caused by control lags or difficult system dynamics, or a combination of these factors, they are in practice difficult to eliminate. SUMMARY [0004] One objective of the present disclosure is to improve the state-of-the-art type of automated painting systems such that the transients disappear or at least become less visible. It is a further objective to propose improved ways of controlling the output pressure of the paint supply system more stably. In particular, it is an objective to control a pressurizing means in the paint supply system without inconvenient time lags. [0005] At least some of these objectives are achieved by the invention as defined in the independent claims. The dependent claims relate to advantageous embodiments. [0006] In a first aspect of the present disclosure, there is provided a painting system comprising: a paint nozzle configured to dispense paint onto a surface; an arm configured to move the paint nozzle over the surface in accordance with an image sweep pattern; pressurizing means operable to feed paint into a paint supply line which extends up to the paint nozzle; and a controller, which is arranged to control the pressurizing means and configured with a control law that includes a feedback component for maintaining an output paint pressure ^ of the paint supply line at a setpoint value ^∗. According to said first aspect, the control law further comprises a feedforward component, which depends on image data in a region which is next to be printed according to the image sweep pattern (i.e., assuming the image sweep pattern is followed), wherein the region is part of a predefined or user-defined image. [0007] The inventors propose to add a feedforward term to the control law, such that the pressurization of the paint supply line is controlled in accordance with a sliding lookahead area into the image that is being printed. The lookahead area follows the predetermined sweep pattern which the paint nozzle follows. The feedforward component may ensure, with proper tuning, a suitable pressure buildup before an episode of high paint flow starts and/or a pressure fadeout when the end of such a high-flow episode approaches. The feedforward component may be described as a predictive component of the control law since it is based on image data from a not yet printed area (lookahead area) of the image, one which will be printed in the near future. [0008] In a second aspect of the present disclosure, there is provided a method of printing a user-defined image onto a surface. The method comprises: dispensing paint from a paint nozzle while the paint nozzle is moved over the surface in accordance with an image sweep pattern; sensing an output paint pressure ^ of a paint supply line which extends up to the paint nozzle; and feeding a flow of paint into the paint supply line so as to maintain an output paint pressure ^ of the paint supply line at a setpoint value ^∗. According to the second aspect, the image printing method further comprises determining, from image data in a region (of the user- defined image) next to be printed according to the image sweep pattern, an adjustment (or compensation) to be applied to said flow of paint. [0009] When a painting system is operated according