GB2398362A

GB2398362A - Hysteresis compensation of actuating elements

Info

Publication number: GB2398362A
Application number: GB0319726A
Authority: GB
Inventors: Andrea Gentile; Daniel Murdock; Axel Hertling; Jeffrey Steven Arsenault
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2003-02-06
Filing date: 2003-08-22
Publication date: 2004-08-18
Also published as: DE10305332B4; GB0319726D0; DE10305332A1; FR2851057B1; FR2851057A1

Abstract

A method for hysteresis compensation of actuating elements driven by actuators, whereby due to the elasticity of the total system, particularly the mechanical backlash in the components participating in the movement and the elastic deformation of the actuating element, housing and actuator, a positional deviation - the hysteresis - occurs, particularly used with flap valves in air conditioning systems, whereby a unique mechanical position equal for either direction of movement is assigned to each controlled position (electrical position). The method is characterized in that: ```the method of hysteresis compensation is only used, if the actuating element is not driven to an end position, ```the method of hysteresis compensation is only used, if the actuator previously changed the direction of movement, ```after a change of direction of movement, that number of compensation steps of the actuator which corresponds to the hysteresis of the total system, to the amount of hysteresis are made, and ```only then the control steps of the actuating element changing the position in the new direction of movement are counted to determine the actual mechanical position of the actuating element.

Description

HYSTERESIS COMPENSATION OF ACTUATING ELEMENTS

The invention relates to a method for hysteresis compensation of actuating elements driven by actuators at the change of the direction of movement, particularly of flap valves in air conditioning systems.

Devices of the above mentioned kind are aimed at compensating the hysteresis of actuating elements driven by actuators when changing the direction of movement, whereby a positional deviation-the hysteresis, is caused by the elasticity of the total system, particularly the mechanical backlash in the components participating in the movement and the elastic deformation of the actuating element, housing and actuator.

Application is, particularly, with flap valves in air conditioning systems, whereby a unique mechanical position equal for either direction of movement is assigned to each controlled position (electrical position).

The high degree of precision required for the movement of the flap valves can only be ensured if the controlling system really takes the desired mechanical position. For that it is necessary to compensate for the backlash occurring when the direction of movement of the flap valve is changed.

It was the object of the following methods and devices to solve comparable problems.

Similar methods to consider the hysteresis error in controlling the scanner drive of an electron miscroscope were used in the US patents 5, 646,403 and 5,780,853. This scanner drive is realized using threaded spindles and stepper motors. - 2 -

The micro step control is completed by an indexing error memory. The determined hysteresis value is stored in this memory and considered during control of the motor. Movements in different directions are also stored.

US patent 6,085,044 also deals with the drive control of an optical apparatus and with the appropriate method of drive control. In this case components for the storage of the drive direction and determination of the position of the driven component are used. If the actual position deviates from the position previously stored, the deviation of the movement is also stored.

US patent 4,042,869 describes another method of hysteresis compensation. At the change of the direction of the actuating element's movement a hysteresis compensation is performed.

When driven by a stepper motor, the position of the actuating element is checked after each step, until the actuating element begins to move too. Actuating elements with automatic or manually controlled drives are provided.

In US patent 3,560,830 a control system for the positioning of machine elements is described which is able to compensate for the backlash of mechanical joints in connection with a number of pre-determined input commands. It includes a motor drive, a pulse generator, a first and a second controller the input of which is connected to the output of the pulse generator and the output of which is connected to the drive.

The first controller transmits pulses of the pulse generator to the drive to position the machine elements. The second controller transmits the pulses of the pulse generator to the drive to compensate for the hysteresis in the machine - 3 element. Further, the system includes a direction comparator to compare the direction component of the input command with the direction component of the input command immediately preceding. The direction comparator is connected to the inputs of the first and the second controllers. The direction comparator activates the first controller, when the direction components are equal, and activates the second controller, when the direction components oppose each other.

Correspondingly, the second controller provides for hysteresis compensation.

A numerical control error compensation system, which relates a previously measured position error to the commanded value of the movement, is described in US patent 4,251,761.

Particularly, it is used at the change between forward and backward motions.

On the whole, it is common to the solutions of the state of the art that they cannot provide a solution easy to realize for the desired compensation of hysteresis in the drive of the flap valve in air conditioning systems. In addition, the specification of the application in the field of air conditioning systems requires to consider the special conditions of this application and the related necessity of an indexing error check. The application, further, must not be limited to stepper motors as drives, but must include different types of actuator drives. Furthermore, the methods used up to now mostly generate different control curves, dependent on the previous direction of movement of the actuating element. - 4

It is, therefore, the object of the invention to develop a method according to the generic part of claim of the invention such that the hysteresis compensation of actuating elements at the change of the direction of movement in the drive of flap valves in air conditioning systems is realized by actuators, whereby a unique mechanical position equal for either direction of movement is assigned to each control position (electrical position).

The problem is solved by a method for hysteresis compensation of actuating elements when a positional deviation, i.e. hysteresis, occurs at the change of the direction of movement when driven by actuators. This is caused by the elasticity of the total system, particularly the mechanical backlash in the components participating in the movement and the elastic deformation of the actuating element, housing and actuator.

The method is, particularly, used with flap valves in air conditioning systems, whereby a unique mechanical position equal for either direction of movement is assigned to each control position (electrical position).

The method of hysteresis compensation is only used, if the actuating element is not driven to an end position. The control command must relate to a mid-position.

Further, the method of hysteresis compensation according to the invention is only used after a change of the direction of movement of the actuator.

If both above mentioned requirements are met, the number of compensation steps which correspond to the amount of hysteresis are made by the actuator after the change of the direction of movement. Exactly that amount of movement is controlled which corresponds to the amount of hysteresis.

Only then the control steps of the actuating element changing the position in the new direction of movement are counted to determine the actual position.

During the movement the end position is determined to ensure that the hysteresis compensation is only made in positions between the two end positions. In the end positions themselves, other methods to ensure exact positioning take the place of the compensation of hysteresis.

The following advantages are offered by the method according to the invention: an exact mechanical position of the flap valve is controlled; each flap valve is controlled individually; the system is flexible.

In the following, the invention is exemplarily described by means of examples of embodiment taking reference to the figures, which show: Fig. 1: Flow diagram of the method of hysteresis compensation; Fig. 2: Actuating element after movement in direction A-B; Fig. 3: Actuating element after movement in direction B-A following a previous movement in direction A-B and representation of the hysteresis H; - 6 - Fig. 4: Actuating element after movement in direction B-A following a previous movement in direction A-B and representation of the hysteresis H after hysteresis compensation; Fig. 5: Motion diagram showing the inaccuracies in positioning caused by hysteresis.

Fig. 1 shows, by a flow diagram, the hysteresis compensation, or the decision whether to use it, respectively, when operating the control of the actuator. The individual steps of the process are represented.

Step 1: The process starts after the motor has stopped.

Step 2: If a new control command is issued, the process goes to step 3; if not, the program stops immediately.

Step 3: If the direction of movement of the actual command is opposite to that of the previous direction of movement, step 4 follows; if not, step 5 follows.

Step 4: Adding of the predetermined number of steps corresponding to the amount of hysteresis in the new direction, without considering this number of steps when the actual position of the actuating element is determined.

Step 5: Continuation with the normal step sequence of the control of the actuator to move the actuating element, corresponding to the original command to move the actuating element. These steps are then counted to determine the actual position of the actuating element. - 7

Fig. 2 shows the actuating element during or following a movement in direction A-B, i.e. going away from the end position AO (100%). The actuator 2 is seen. According to an advantageous embodiment of the invention, this actuator is designed to be a stepper motor. The components arranged between actuator 2 and actuating element 1 passed by the flux of force cause a backlash. This results in a hysteresis H when the direction of movement is changed, i.e. a difference between the angular position of the actuating element, as, (mechanical position) and the angular position of the actuator, aA, (electrical position).

Fig. 3 shows this state in which a difference between the angular position of the actuating element, as, (mechanical position) and the angular position of the actuator, as, (electrical position) is observed as hysteresis H. In Fig. 4, the hysteresis compensation became effective by considering the hysteresis H. before the actuating element had taken the required mechanical position.

The diagram of Fig. 5 is a motion diagram which shows the inaccuracies of positioning caused by hysteresis. Graph shows the ideal course as represented by the control software of the actuator without considering any hysteresis compensation. Practically, however, there is a hysteresis within the amount Y after the direction of movement has been changed. In case X the actuating element moves from AO to BO (100% after 0 of the mechanical position). Then the drive stops, and a change of the direction of movement follows. But instead of moving back on the ideal way in direction of end position AO, the actuating element remains in the mechanical 8 - position reached. The actuator moves by the number of steps (Y) which correspond to the amount of hysteresis. With the actuator performing this movement the electrical position changes, and a difference between the mechanical and electrical positions in the amount of hysteresis results.

Only after the actuator has made the number of steps which correspond to the amount of hysteresis, the actuating element starts to move in direction A0, movement Z in the diagram.

The software, therefore, controls the actuator to the graph Skimp, whereby the hysteresis has already been considered and compensated for, so that a superposition of the required movement of the actuating element and the hysteresis is represented.

The method of hysteresis compensation is only used, if the actuating element is not driven to an end position. The control command must therefore relate to a mid-position, e.g. 40%, provided the end positions are designated 0 and 100%, respectively.

Also, the method of hysteresis compensation according to the invention is only used, if the actuator previously performed a change of the direction of movement. This is the case if there was a sequence of commands to reach the angular positions 40%-45%-30%, which includes a change of direction of movement. Commands to reach the angular positions 40%-45% 50% imply no change of direction of movement and no hysteresis compensation is used.

In one embodiment, the amount of hysteresis for the system is defined and the hysteresis compensation correspondingly regulated. In the other case, the amount of hysteresis is - 9 continuously measured anew and the hysteresis compensation correspondingly controlled. Sensors measure the actual amount of the hysteresis.

In connection with the hysteresis compensation different strategies are applied in combination or independently, to ensure trouble-free, precise function of the actuating element. These include: - the cold start strategy of the actuator; - the calibration of the actuating element; the identification of situations which imply stalling of the actuator; the determination of the end positions of the actuating element; - the compensation of the backlash of the actuating element when an end position has been reached; - the starting strategy until the necessary nominal torque has been reached.

These methods are utilized in connection with the method according to the invention.

The disclosures in German patent application No. 10305332.8, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Nomenclature Actuating element Actuator End position AD End position BO Driving shaft of the actuator Controller Controller including hysteresis measurement End position sensor Amount of the hysteresis H Angular position of the actuating element, as Angular position of the actuator, aA

Claims

Claims 1. A method for hysteresis compensation of actuating elements

driven by actuators, whereby due to the elasticity of the total system, particularly the mechanical backlash in the components participating in the movement and the elastic deformation of the actuating element, housing and actuator, a positional deviation - the hysteresis - occurs, particularly used with flap valves in air conditioning systems, whereby a unique mechanical position equal for either direction of movement is assigned to each controlled position (electrical position), characterized in that the method of hysteresis compensation is only used, if the actuating element is not driven to an end position, the method of hysteresis compensation is only used, if the actuator previously changed the direction of movement, after a change of direction of movement, that number of compensation steps of the actuator which corresponds to the hysteresis of the total system, to the amount of hysteresis are made, and only then the control steps of the actuating element changing the position in the new direction of movement are counted to determine the actual mechanical position of the actuating element.
2. A method according to Claim 1, wherein in the course of movement, when an end position is reached, this end position is determined.
A method according to Claim 2, - 12 wherein the determination of the end position is made to ensure that the hysteresis compensation is only used in positions between the two end positions.
4. A method according to one of the preceding claims, wherein the amount of hysteresis is predetermined and the hysteresis compensation is regulated.
5. A method according to any one of claims 1 to 3, wherein the amount of hysteresis is continuously measured anew and the hysteresis compensation is controlled.
6. A method according to claim 5, wherein the actual amount of the hysteresis is determined by means of sensors.
7. A method for hysteresis compensation substantially as herein described with reference to the drawings.