GB2334792A

GB2334792A - Adaptive control of overshoot in the position of a member

Info

Publication number: GB2334792A
Application number: GB9902222A
Authority: GB
Inventors: Gerard J Schorn; Thomas S Soistmann
Original assignee: Langston Corp
Current assignee: Langston Corp
Priority date: 1998-02-06
Filing date: 1999-02-02
Publication date: 1999-09-01
Also published as: JPH11268154A; ES2152875B1; GB9802464D0; GB9902222D0; FR2775365B1; FR2775365A1; DE19904664A1; SE9900395L; ES2152875A1; ITMI990242A1; SE9900395D0; IT1308345B1

Abstract

A controller 44 is provided for adaptively controlling the movement of a member, such as a roller or a guide, of a machine to a desired position. The controller calculates a command position by subtracting a predetermined overshoot value from the desired position. The controller signals a member 16, 18 of a machine to move to the command position. A sensor 40, 42 determines the actual position of the member. The controller calculates an updated overshoot value by subtracting the actual position from the command position and controls a succeeding movement of the member as a function of the updated overshoot value. Compensation may also be made for ambient temperature changes, changes in air pressure if the motor is air-driven, changes in voltage or current if it is electrically driven.

Description

ADAPTTVE CONTROL METHOD AND DEVICE Field of the Invention The invention relates to a controller and method for accurately positioning an axis or movable member in a machine, and in particular for automatically setting up the axes in a corrugating machine and/or a box making machine.

Background of the Invention Corrugating machines and/or box making machines typically rely on a large number of rollers, such as corrugating rollers, print rollers, pressure rollers, slitter/scorer rollers, side guides, and other members which must be properly aligned and positioned. Each roller rotates about a central axis. For proper operation of the machine it is necessary for all of the axes be properly aligned with respect to each other and with the rest of the machine.

Presently, alignment of the axes, or "set-up," is done by a computer controller. Typically the axis of each positionable roller is positioned using set-up signals to drive air motors and lead screws. As might be expected, there is always an overshoot or "deadband" because the motors, lead screws, and other mechanical parts cannot stop in time to position the axes precisely at their preselected locations.

Presently, a "brute force" method is used to compensate for the deadband. A set-up routine is run periodically to gauge the amount of overshoot or deadband and subtract it from the set-up signals. This requires the machines to be taken out of production for a period of time each week. Since down time translates into lost money, the machine operators do not like to run the set-up routine, and thus the machine tends to become severely unaligned fairly quickly.

The present invention avoids the drawbacks of existing set-up techniques by continuously monitoring and actually measuring the deadband values as the machine is running, and continuously updating the deadband values based on the measured values.

Summarv of the Invention A controller is provided for adaptively controlling the movement of a member or axis, such as a roller or a guide in a corrugating machine, to a desired position. The controller calculates a command position by subtracting a preselected deadband value from the desired position. The controller signals a member of a machine to move to the command position. A sensor determines the actual position of the member. The controller calculates an updated deadband value by subtracting the actual position from the command position and controls a succeeding movement of the member as a function of the updated deadband value.

The controller may be programmed to average the updated deadband value over a preselected number of member movements. When an average deadband value is calculated, succeeding movements of the member are determined as a function of the average updated deadband value.

A sensor, such as an encoder, may be used to determine the actual position of the member.

The controller may operate during an operational movement, i.e., a normal set-up move of a machine while the machine is in service, during a manual targeting move, and during specific set-up moves, to determine the updated deadband value.

Brief Description of the Drawings For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

Figure 1 is a schematic representation of the adaptive control device of the present invention as used with a moveable side guide system of a flexofolder gluer machine.

Figure 2 shows a flow chart diagram for the operation of the adaptive control device.

Detailed Description of the Invention In Figure 1 there is shown an adaptive control device 10 in accordance with the present invention. The adaptive control device is shown in combination with a moveable side guide mechanism 11 of a flexofolder gluer machine; however, it is understood that the control device could be adapted for use with any machine having a movable member or axis, such as a roller or a guide. The side guide mechanism 11 includes a shaft 12 which is disposed on a frame 14. A pair of side guides 16 and 18 are slideably disposed at opposite ends of the shaft 12. A displacing device 20 translates the side guides 16 and 18 laterally along the shaft 12 as shown by the arrows 21. In the embodiment shown, the displacing device 20 comprises a pair of air motors 22 and 24 and a gear box 26. Note: The lead screws could be driven by numerous types of AC or DC motors controlled by a contractor instead of a valve.

The air motor 22 drives a lead screw 32 which is operatively connected to the side guide 16. A support member 34 is mounted at the center of the shaft 12. The distal end 33 of the lead screw 32 is rotatably mounted in a bearing 35 located in the center support member 34. Similarly, the air motor 24 drives a lead screw 36 which is operatively connected to side guide 18. The lead screw 36 is rotatably supported by a bearing 37 in the center support member 34. The distal end 39 of the lead screw 36 is rotatably mounted in a bearing 38 in the frame 14. The air motors 22 and 24 drive the lead screws 32 and 36, respectively, which translate the side guides 16 and 18 laterally along the shaft 12.

Position sensors, such as encoders 40 and 42, associated with the servo air motors 22 and 24 determine the exact location of the side guides 16 and 18 on the shaft 12. Signals proportional to the distance travelled by the side guides 16 and 18 are transmitted from the encoders 40 and 42 to a controller 44, which may be a microprocessor or a programmable logic controller or the like.

The controller 44 processes the signals received from the encoders 40 and 42 and transmits a command signal to a pair of control valves 46 and 48. The control valves 46 and 48 control the operation of the air motors 22 and 24 to position the side guides 16 and 18 at the desired location.

There is always an overshoot, or "deadband," because the motors, lead screws, and other mechanical parts cannot stop in time to position the side guides precisely at the desired location. The adaptive control device 10 continuously monitors and actively measures the deadband as the machine is running, as described below.

Referring to Figure 2, initially, when the machine is manufactured, an initial deadband value is placed in the controller memory.

This initial deadband value is determined from historical data for similar machines. In operation, the operator enters a distance that the side guides 16 and 18 are desired to be moved or the computer calculates the desired position based on the order set-up requirements, such as a distance of thirty inches. If the initial "deadband" was determined to be 0.1 inch, then the side guides 16 and 18 will typically overshoot the desired position by 0.1 inch due to response delays in the valve and motor and lost motion in the lead screw.

To compensate for this deadband, the controller 44 calculates a command position by subtracting the initial deadband value from the desired position. The controller 44 then sends a signal to the control valves 46 and 48 to operate the motors 22 and 24 and drive the lead screws 32 and 36, displacing the side guides 16 and 18 by this calculated command position.

For example, if the desired position was 30 inches and the initial deadband was 0.1 inch then the command position would be 29.9 inches. In other words, the controller would actually command the side guides to stop when the measured position was 29 9 inches. By the time the side guides actually stopped because of the inherent overshoot, they would be approximately at the 30 inch mark.

After the side guides 16 and 18 are moved to the command position, the actual position of the side guides is determined by the encoders 40 and 42. The value is stored in the controller's memory. A counter is incremented to indicated the number of times the side guides have been moved.

The controller then calculates an average deadband based on the new positional data received from the encoders. The deadband is determined by subtracting the actual position from the command position. This value is added to an "axes position difference" register. The axes position error difference is then divided by the increment counter N to obtain the average deadband value. This result is stored as the new deadband value. It is understood that the new average deadband could be calculated by any conventional averaging routine. At this point the counter is compared to a preselected maximum limit to determine if the maximum number of iterations have been reached.

For example, when the preselected limit is ten, the next ten times the side guides are moved, the controller will calculate a separate deadband value for each movement to obtain an average for those ten movements. Once the limit value is reached, the prior or initial deadband value is replaced with the newly calculated deadband value. Thus, for the next move of the side guides 16 and 18, the new command position will be equal to the new desired position minus the updated deadband value.

The deadband routine is run on a continuous basis to compensate for changes in the system caused by wear or the environment. The adaptive controller 10 does not require the machine to be taken out of service to calculate the new deadband value. The adaptive controller can use any axis move, including normal computer calculated set-up moves, manual targeting moves, and specific moves to determine the new deadband. The system could also compensate for environmental changes by using sensors to compensate for temperature change or variation in shop air pressure, for example. In addition, if an electrical actuator is employed instead of an air motor, for example, variations in voltage or current can also be compensated for. The major advantage to the system is that no separate deadband routine need be run which would result in lost production time. The system will always be using the optimum deadband values and the operator does not have to remember to run a separate routine.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.

Claims

CLAIMS 1. A method for adaptively controlling the movement of a member of a machine to a desired position, comprising the steps of: calculating a command position by subtracting a preselected deadband value from a desired position; signalling a member of a machine to move to the command position; determining the actual position of the member; calculating an updated deadband value by subtracting the actual position from the command position; and controlling a succeeding movement of the member as a function of the updated deadband value.
2. A method for adaptively controlling according to claim 1 further comprising the step of: averaging the updated deadband value over a preselected number of member movements; and wherein the controlling step comprises controlling a succeeding movement of the member as a function of the average updated deadband value.
3. A method for adaptively controlling according to claim 1 or 2, wherein the determining step comprises using a sensor to determine the actual position of the axis.
4. A method for adaptively controlling according to claim 3, wherein the sensor is an encoder.
5. A method for adaptively controlling according to any one of claims 1 to 4, wherein the signalling step is performed during an operational movement of the machine while the machine is in service.
6. A method for adaptively controlling according to any one of claims 1 to 5, wherein the member comprises a roller, rollernips or a guide of a corrugating machine.
7. A method for adaptively controlling according to any one of claims 1 to 6, wherein the step of controlling a succeeding movement of the member comprises controlling said succeeding movement as a function of the updated deadband value and an ambient condition.
8. A method for adaptively controlling according to claim 7, wherein the ambient condition is temperature.
9. A device for adaptively controlling the movement of a member of a corrugating machine to a desired position, comprising: means for calculating a command position by subtracting a preselected deadband value from a desired position; means for signalling a member of a corrugating machine to move to the command position; a means for determining the actual position of the member; means for calculating an updated dead band value by subtracting the actual position from the command position; and a controller for controlling a succeeding movement of the member as a function of the updated deadband value.
10. A device for adaptively controlling according to claim 9 further comprising: means for averaging the updated deadband value over a preselected number of member movements; and wherein the controller comprises controlling a succeeding movement of the member as a function of the average updated deadband value.
11. A device for adaptively controlling according to claim 9 or 10, wherein the determining means comprises a sensor for determining the actual position of the member.
12. A device for adaptively controlling according to claim 11, wherein the sensor is an encoder.
13. A device for adaptively controlling according to any one of claims 9 to 12, wherein the signalling means operates during an operational movement of the corrugating machine while the corrugating machine is in service.
14. A device for adaptively controlling according to any one of claims 9 to 13, wherein the member comprises a roller or a guide of the corrugating machine.
15. A device for adaptively controlling according to any one of claims 9 to 14, further comprising a sensor to sense an ambient condition and provide a signal representative of said ambient condition to said controller for controlling a succeeding movement of the member as a function of the average updated deadband value and said ambient condition.
16. A device for adaptively controlling according to claim 15, wherein said ambient condition is temperature.
17. A method for adaptively controlling the movement of a member of a machine to a desired position substantially as hereinbefore described with reference to the accompanying drawings.
18. A device for adaptively controlling the movement of a member of a machine to a desired position substantially as hereinbefore described and as illustrated in the accompanying drawings.