CA2723610C

CA2723610C - Method for determining dead zone of valve

Info

Publication number: CA2723610C
Application number: CA2723610A
Authority: CA
Inventors: Jussi Puura; Markus Saarela
Original assignee: Sandvik Mining and Construction Oy
Current assignee: Sandvik Mining and Construction Oy
Priority date: 2008-05-13
Filing date: 2009-05-11
Publication date: 2013-07-16
Anticipated expiration: 2029-05-11
Also published as: AU2009247995B2; CN102027185A; JP2011522174A; CN102027185B; CA2723610A1; EP2310611A4; FI120918B; JP5319759B2; AU2009247995A1; FI20085445A0; WO2009138558A1; FI20085445A; EP2310611A1

Abstract

The invention relates to a method for determining the dead zone of a proportional control valve (8) used for controlling an actuator of a rock drilling device, the method comprising controlling the control valve (8) with an electric P controller (12) and measuring the position of the actuator in a coordinate system representing its movement with a separate position detector.
The dead zone is determined by means of a product of the P controller of the control valve (8) and the difference value.

Description

I
METHOD FOR DETERMINING DEAD ZONE OF VALVE

BACKGROUND OF THE INVENTION
[0001] The invention relates to a method for determining the dead zone of a proportional control valve used for controlling an actuator of a rock drilling device, the method comprising controlling the control valve with an electric P controller and measuring the position of the actuator in a coordinate system representing its movement with a separate position detector.

[0002] In a hydraulic rock drilling apparatus, actuators as feed beam cylinders of booms are controlled by using proportional directional control valves. In practice, this involves controlling the actuator in both directions, whereby, when the valve is in the middle position, i.e. in the 0 position, the actuator does not move, and when the valve spool is displaced in either direction, the actuator moves at a proportional speed relative to the spool offset in such a way that the more the spool deviates from the 0 position, the faster the actuator operates.

[0003] However, in present control systems it has been noted that when the valve is operating, there is typically what is called a dead zone on both sides of the 0 point where no pressure fluid flows to the actuator in spite of a control signal.

[0004] If this dead zone of the valve is known, control can be corrected by taking the dead zone into account and by forming in an electric control signal, for example, an initial offset value of the extent of the dead zone when starting from the 0 position, so that the initial value of the control signal is equal to the required error.

[0005] In practice this is not feasible, however, because the dead zone varies valve-specifically. Further, the dead zone may be different in different operating directions of the valve. Different valves also have dead zones of different extents, so one single value to correct this matter does not exist.

BRIEF DESCRIPTION OF THE INVENTION

[0006] An object of this invention is to provide a method with which the operation of a hydraulic actuator of a rock drilling device can be made more accurately controlled than before.

[0007] The method according to the invention is characterized by the method comprising the steps of:

(a) setting for the P controller, for controlling the control valve (8), the first value of the controller gain to be 0 or such a value that the actuator is not expected to move due to the effect thereof, and setting for the actuator a target value deviating from its current value, whereby the difference between the current value and the target value of the actuator determines the first difference value;
(b) adding to the value of the controller gain a value increment of the extent of a predetermined step for the P controller for controlling the control valve;
(c) waiting for a predetermined time to establish whether the position value given by the position detector of the actuator expresses that the actuator has begun to move;
(d) if, on the basis of the position value of the position detector, the actuator has begun to move, moving to step (f);
(e) repeating steps (b) to (c) until, on the basis of step (d), it is time to move to step (f);
(f) waiting until the movement of the actuator has, on the basis of the position detector of the actuator, stopped, and determining a second difference value as a difference value between the target position and the position of the moment of stopping;
(g) determining at least one offset value in accordance with steps (h) and/or (i) and storing it in memory to be used for compensating for the dead zone of the control valve when controlling the control valve;
(h) determining a first offset value as a product of the P controller gain according to step (d) and the first difference value according to step (a);
(i) determining a second offset value as a product of the P controller gain according to step (d) and the second difference value according to step (f).
[0008] An essential idea of the invention is to determine for each control valve at least one control offset value corresponding to the dead zone in the middle of the movement range of the control valve spool and, each time the valve is controlled, taking into account the dead zone in the direction of motion of the valve. One embodiment of the invention comprises determining for each control valve in both directions of motion at least one control offset value corresponding to the dead zone and controlling the valve in both directions of motion by using the corresponding offset value to compensate for the dead zone of the valve.

[0009] An advantage of the invention is that a simple method enables definition of the properties of each valve and of the valve-specific dead zone in both directions of motion of the valve, if required, in the control system, whereby, when controlling the actuator, the dead zone of the valve can be virtually eliminated irrespective of whether the error is purely due to valve properties or caused by the valve properties and the control electronics together.

BRIEF DESCRIPTION OF THE INVENTION

[0010] The invention will now be described in greater detail in the attached drawings, in which Figure 1 shows schematically an actuator of a rock drilling device;
Figure 2 shows schematically an exemplary characteristic curve of a proportional directional control valve and the value of the control signal required by it;
Figure 3 shows schematically a block diagram of a solution applicable to the control of a valve and an actuator;
Figure 4 shows schematically a flow chart for applying the method according to the invention.

[0011] For the sake of clarity, embodiments of the invention are shown simplified in the figures. Similar parts are denoted with the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Figure 1 shows schematically an actuator in a rock drilling apparatus. Reference numeral 1 indicates schematically a base to which a boom 3 is turnably connected by means of a joint 2. The boom 3 can be turned around the axis of the joint 2 with an actuator, i.e. a hydraulic cylinder 4, which is connected by its one end to the base I with joints 5, and correspondingly by its other end turnably to the boom 3 with a joint 6. In order to control the hydraulic cylinder 4, pressure medium from a pump 7 can be fed into it via a proportional control valve 8, whereby from the other end of the hydraulic cylinder 4, pressure fluid flows into a pressure fluid container 9 also via the valve 8. In order to control the hydraulic cylinder 4, the proportional control valve 8 is controlled with a control unit 10, to which also sensors 11 indicating the turning angle of the boom are connected. Further, the figure shows a feed beam 12 at the end of the boom 3, along which a drilling machine 13 and a drill rod 14 connected thereto move when a hole is being drilled in rock 15. Various turning cylinders or rotary motors for turning the feed beam relative to the boom, feed apparatuses for moving the drilling machine and other actuators are generally known as such and since they do not essentially relate to the invention, there is no need to show them in the drawings or explain them in the description in more detail.

[0013] Figure 2 shows schematically a typical characteristic curve of a valve, where straight line A indicates a theoretical characteristic curve of the valve, i.e. the relation of the control signal arriving at the valve and the amount of flow of the pressure fluid passing through the valve. Correspondingly, straight lines B1 and B2 show real control signals of the valve operation and the volume flows of the pressure fluid passing through the valve.

[0014] As seen from the figure, the relation of the control signal and the volume flow passing through the valve is such that when the control signal is 0, the volume flow is also 0, and depending on the value of the control signal, the volume flow through the valve changes linearly from zero in one direction or the other.

[0015] In practice, there is a dead zone in the operation of the valve either as a property of the valve or due to the combined effect of the valve property and control electronics, this dead zone being +-20 units in Figure 2.
Therefore, volume flow through the valve does not begin until the value of the control signal is 20 units in one direction or the other, and only above this value does the volume flow of the pressure fluid follow the value of the control signal through the valve.

[0016] If the situation were this ideal with all control valves, this would be easily corrected by setting, in the control unit, the offset required by the dead zone in the control signal of the valve. In practice, this is not feasible because the dead zone of each valve and of the direction of motion of each valve spool is individual.

[0017] Figure 3 shows schematically a block diagram of a solution applicable to controlling a valve actuator. The figure shows a controller 16, which is a part of a control unit or which may be formed by a computer program or a part of it in the control unit. The controller 16 is connected to control an entity 17 formed by a control valve 8 and an actuator with a control signal which is proportional to the difference value between the measured position of the actuator and the desired position and which is here generally referred to as control. The controller 16 is what is called a P controller, i.e. it controls the valve and via that the actuator in such a way that it is directly proportional to the control signal arriving at it. Further, the figure shows schematically a summing unit 18, to which an offset value and a control signal given by the controller 16 are brought to control the valve. On the basis of these, final control is generated for the control valve in the summing unit 18.
[0018] Calibration of the valve and actuator operation is performed by first setting for the controller the gain value 0 or such a value with which the control valve does not yet begin to let pressure fluid to the actuator. At this stage, the offset value is naturally 0. After this, a target value is set for the actuator to be controlled, i.e. a position value deviating from the current position, so that the difference value between the current position and the desired position of the actuator will be a given value, for example in calibration a turning angle of 1 or for linear movement 1 m. Naturally, also other numerical values relative to the angle or linear movement are feasible. The gain value of the P controller gain may also be a value other than 0, as far as the control provided by the product of the gain value and the difference value does not generate actuator movement. In practice, the gain value and the target value for determining the difference value can be set in any order or even simultaneously. Thus, in step (a) of claim 1, the intention is not to have determination of the values in the particular order mentioned but the setting order may be any of the above-mentioned orders.

[0019] When the P controller gain is 0, the valve control is 0. This is due to the valve control being, at each moment of time, the controller gain multiplied by the difference value of the actuator. When the controller gain is sufficiently low, the actuator does not begin to move because the product of the gain and the difference value does not exceed the control gain required by the valve.

[0020] Next, the value of the P controller gain is increased. For example value 1 may be set as gain, whereby P controller gain x difference value, for example 1, is obtained as the value of the valve control.

[0021] At this stage, one must wait for some time, for example 0.5 seconds or, depending on the device, longer in order to see on the basis of the signal arriving from the position detection sensor whether this control fed to the control valve generates actuator movement, which would mean that the position of the actuator begins to move towards the target position. If such movement is not detected, P controller gain is increased with predetermined increments, i.e. steps, one step at a time, and after each increment, there is a waiting period in order to detect possible movement of the actuator before the P controller gain can be further increased. When movement is detected in the actuator, the first offset value is the same as the controller gain multiplied by the above-mentioned difference value of the initial position and the target position of the actuator.

[0022] If offset in the actuator is detected as early as after the setting of the first gain value, there is no dead zone in the control valve, and the volume flow of the pressure fluid generating from the valve control may, even with this minimum control, be too great to achieve a good control result.

[0023] On the other hand, when the actuator has started moving, the first offset value according to the product of the gain value, which has generated the movement and has been set for the P controller, and the difference value is stored in memory, and it may be later used for controlling the valve and thus the actuator.

[0024] When the actuator has started to operate as a result of the control valve being opened, the valve control starts to decrease because its value is the product of the P controller gain and the remaining difference value.
The difference value is here the distance between the target position and each particular momentary position. When the actuator continues the movement, the value of the valve control is reduced, and at some point, the actuator stops moving because the value of the control valve control is reduced with the reduction of the difference value to such an extent that the control valve stops letting pressure fluid to the actuator and closes. The movement of the actuator may, of course, stop because the actuator achieves the target position, the difference value being thus 0. The second offset value of the control valve, at which the closing took place, is obtained by multiplying the gain set for the P
controller by that difference value of the actuator which was the offset at the end of the movement, and this second offset value is stored in memory. This product of the P controller and the difference value, obtained when the actuator movement stops, is the second offset value relative to the control valve control and represents the dead zone in the middle area of the valve in the valve operation. In reality, this gives both the first offset value of the valve control, representing the offset required for starting the valve control, and the second offset value of the valve control, representing the offset that remained when the valve control ended. These two values differ from each other, and when the valve is controlled later, both values, only one value or some value between them can be used for compensating for the dead zone. Likewise, since these values are usually different in different directions of motion of the valve spool, it is possible to use only one offset value in both directions of motion or a separate offset value in each direction. In embodiments requiring extreme accuracy, both offset values obtained may naturally be used in both directions of motion.

[0025] This determination of the dead zone of the control valve is shown schematically in Figure 4, which illustrates an example of determining the offset value, i.e. the dead zone, as a flow chart when both the first and the second offset value are determined.

[0026] In Figure 4 gain Kp, i.e. control value, of the P controller has been set to 0 in the first step 21 of the flow chart, due to which the control valve does not obtain control and therefore the actuator cannot move either.

[0027] Next, step 22 comprises setting position value 1 as reference value Ref relative to the current position of the actuator, as well as the desired direction of motion. This value I may be for example 11' at a turning angle, 1 m in linear movement or another suitable value expressed, by way of example, as number 1.

[0028] Subsequently, in step 23, the current gain value Kp added by one, i.e. Kp = Kp + 1, is set as the gain of the P controller .
Correspondingly, one means here one predetermined extent of a step, which is expressed, by way of example, with number 1.

[0029] This done, one must wait in step 24 as a consequence of the gain value in question to see whether the value causes movement in the actuator. This movement, if there is any, is detected on the basis of the position value given by the position detector.

[0030] In step 25, a decision about how to proceed is made on the basis of the position value given by the position detector and expressing whether the actuator has started moving. If no movement is detected, one returns to step 23, adding yet one predetermined gain step to the gain Kp of the P controller. The loop of steps 23 to 25 is repeated as long as it is observed in step 25 that the actuator has started moving. Then, in accordance with step 26, the current control value formed by the product of the P
controller gain value and the difference value Ref set in step 22, i.e. the first offset value, offset 1, is stored in memory to be used later for controlling the control valve of the actuator.

[0031] When actuator movement has been detected, one waits in step 27 without making any changes to the control of the control valve.

[0032] In the next step 28, it is checked with the position detector of the actuator whether the actuator is still moving, i.e. whether the position value given by the position detector changes. As long as this value continues to change, one returns to step 27 and, in a predetermined time period, moves to step 28 again to check whether the actuator is moving.

[0033] Once it has been observed in step 28 that the position value of the position detector of the actuator does not change any longer, one moves to step 29, where the difference value between the target position set for the actuator and the position at the stopping moment, i.e. the difference value, is determined. Thus, the second offset value, offset 2, of the control valve, in other words the extent of the dead zone in the middle area of the valve from the 0 position towards the measured direction of motion, is obtained by multiplying the value of the difference value by the gain value of the P
controller. This second offset value is stored in memory, and it may be used in schematic presentation according to Figure 3 by adding the obtained offset value to the control value of the valve irrespective of whether the control system used is analogue or digital, and also when using manual control, for instance joystick control.

[0034] The above method may be implemented automatically in a computer-controlled apparatus, in which case the control may be performed by anyone and there is no need for control specialists. In rock drilling apparatuses having several different actuators, this calibration may be performed automatically for all control valves and actuators controlled by them, in which case separate offset values are obtained for each of them. Control may also be performed in both directions of motion, in which case the different offset values in different directions of motion can be stored for each valve and each actuator. In some cases, sufficient control accuracy is obtained by selecting the offset value from between the initial and final offset values and by using this value for correcting the control. If desired, the same value can be used in both directions of motion.

[0035] The invention is explained only by way of example in the description and drawings, and it is not in any way restricted to what is presented therein. What is essential is that in the operation of a proportional control valve, the dead zone where the valve does not in reality control the actuator is determined in the way described in the claims and that the error value thus obtained is used for compensating for the dead zone of the valve during the use of the device and the control of the valve. Once stored in memory, the offset value or values may be used for controlling the actuator, irrespective of the control manner used in real controlling or the mode of the controller. Thus, the values may be used with P, D and/or l controllers as well as in control systems using both analogue and digital control signals for controlling valves. Likewise, when manual controllers are used for controlling, the control system may take the offset values into account in a desired manner.

[0036] In some cases, features of this application may be used as such, irrespective of other features. On the other hand, features presented in this application may be combined to form various combinations.

[0037] The drawings and the related description are only intended to illustrate the idea of the invention. Details of the invention may vary within the scope of the claims.

Claims

1. A method for determining the dead zone of a proportional control valve (8) used for controlling an actuator of a rock drilling device, the method comprising controlling the control valve with an electric P controller and measuring the position of the actuator in a coordinate system representing its movement with a separate position detector, characterized by the method comprising the steps of:
(a) setting for the P controller, for controlling the control valve (8), the first value of the controller gain to be 0 or such a value that the actuator is not expected to move due to the effect thereof, and setting for the actuator a target value deviating from its current value, whereby the difference between the current value and the target value of the actuator determines the first difference value;
(b) adding to the value of the controller gain a value increment of the extent of a predetermined step for the P controller for controlling the control valve (8);
(c) waiting for a predetermined time to establish whether the position value given by the position detector of the actuator expresses that the actuator has begun to move;
(d) if, on the basis of the position value of the position detector, the actuator has begun to move, moving to step (f);
(e) repeating steps (b) to (c) until, on the basis of step (d), it is time to move to step (f);
(f) waiting until the movement of the actuator has, on the basis of the position detector of the actuator, stopped, and determining a second difference value as a difference value between the target position and the position of the moment of stopping;
(g) determining at least one offset value in accordance with steps (h) and/or (i) and storing it in memory to be used for compensating for the dead zone of the control valve (8) when controlling the control valve (8);
(h) determining a first offset value as a product of the P controller gain according to step (d) and the first difference value according to step (a);
(i) determining a second offset value as a product of the P controller gain according to step (d) and the second difference value according to step (f).

2. A method according to claim 1, characterized by determining both the first and the second offset value in at least one direction of motion of the control valve (8) and storing them in memory to be used for compensating (8) for the dead zone when controlling the control valve (8).

3. A method according to claim 1 or 2, characterized by determining the offset values in both directions of motion of the control valve (8).

4. A method according to claim 3, characterized by using the offset values of both directions of motion to compensate for the dead zone of the control valve (8) only in that direction of motion in which it was measured.

5. A method according to claim 3, characterized by forming from the offset values a value which is between these offset values, preferably a value corresponding to the average, for compensating for the dead zone of the control valve (8) when controlling the control valve (8) in at least one of its directions of motion.

6. A method according to claim 5, characterized by this formed value between the offset values being used for compensating for the dead zone of the control valve (8) when controlling the control valve (8) in both of its directions of motion.

7. A method according to any one of claims 1 to 4, characterized by using the first offset value for compensating for the dead zone of the control valve (8).

8. A method according to any one of claims 1 to 4, characterized by using the second offset value for compensating for the dead zone of the control valve (8).