JPH08309779A - Method and apparatus for controlling position of template of toggle type mold clamping apparatus - Google Patents

Abstract

PURPOSE: To obtain a highly hollow molded product of high quality by controlling the distance between a movable plate and a fixed plate with high accuracy especially in highly hollow molding in a method and apparatus for controlling the position of the template of a toggle type mold clamping apparatus. CONSTITUTION: In a highly hollow molding method, the execution value obtained by measuring the position and speed of a movable plate 12 and a set value or the detection position signals from the crosshead position sensor and tiebar elongation sensor of a toggle type mold clamping apparatus 10 are used and a crosshead 18d is subjected to feedback control to keep the interval between molds constant to perform molding of high quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold platen position control method and device for a toggle type mold clamping device, and more particularly, to a distance between a movable platen and a fixed platen when molding a high hollow molded product by an injection molding machine. The present invention relates to a new improvement for obtaining a high-quality high hollow molded product which is controlled with high precision.

[0002]

2. Description of the Related Art In general, a method of forming a high hollow molded product with an injection molding machine is one in which the mold clamping force is released before it is solidified after the molten resin is filled in the mold by injection and gas is injected into the molten resin. While moving the mold, the movable mold is retracted in synchronism with the gas injection to form the rib and the hollow part. When the molded product retreated to the thickness, it was kept cooling and waited for the molten resin to solidify, then the gas was discharged and the mold was taken out.

[0003]

Since the conventional method for molding a high hollow molded article is configured as described above, the following problems exist. That is, conventionally, when performing this molding method, using a general injection molding machine, with the mold clamping force required for the mold being applied, the retreat control and position of the movable mold during gas injection are performed. The control is performed by a hydraulic cylinder and a sensor provided in the mold. The force due to the gas pressure is considerably large, and the hydraulic cylinder also requires a considerably large one, which is expensive. Therefore, there is a drawback that an expensive mold is required every time the molded product changes. If the hydraulic cylinder in the mold controls the movable mold backward, the amount of backward movement and the value measured by the sensor are 1 to 1. Therefore, the hydraulic control accuracy and the sensor accuracy immediately affect the cylinder position. There is a drawback that the control accuracy is poor and the thickness accuracy of the molded product is poor.

The present invention has been made to solve the above problems. In particular, the injection molding machine side controls the backward stroke of a movable mold (movable plate) during gas injection after injection. As a result, a hydraulic cylinder for retreat control in the die is not required, and it is possible to perform high hollow molding with an inexpensive die, and the retreat control of the movable die (movable plate) is performed by the movable die. Provided are a mold plate position control method and device for a toggle type mold clamping device, which is improved in control accuracy by performing movement with a crosshead that is larger than the retreat amount, and improves thickness accuracy of a high hollow molded product. The purpose is to

[0005]

A method of controlling a mold plate position of a toggle type mold clamping device according to the present invention uses a toggle type mold clamping device to inject a molten resin into a mold after completion of mold clamping, and to perform the melting. Before the resin is solidified, the mold clamping force is released, the gas is injected into the molten resin and the movable plate is retracted, and after the molten resin is solidified and cooled, the gas is discharged to form a high hollow molded product from the mold. Using the execution value and the set value that are measured to control the position and speed of the movable plate or the mold while controlling to take out,
The cross head of the toggle type mold clamping device is feedback-controlled, and speed control is performed until the movable platen reaches the set retreat limit position in the previous period, and when it reaches the retreat limit position, it is switched to the position control that holds that position to discharge gas. This is a method of keeping a constant distance between the movable platen and the fixed platen.

A method of controlling a mold platen position of a toggle type mold clamping device according to the present invention uses a toggle type mold clamping device, in which a molten resin is injected into a mold after the mold clamping is completed, and before the solidification of the molten resin is completed. The mold clamping force is released, gas is injected into the molten resin, the movable plate is retracted, and after the molten resin is solidified and cooled, the gas is discharged and the high hollow molded product is taken out from the mold. Along with it, the backward speed control of the movable plate and the holding control at the backward limit position are calculated and controlled to the backward speed and the position of the crosshead, and the deformation amount of the toggle type mold clamping device generated by the gas pressure is controlled by the tie bar. Measure the amount of change in elongation and calculate the movement distance of the crosshead to control it by controlling the crosshead so that the distance between the movable platen and the fixed platen does not change even if the toggle type mold clamping device deforms. In a way to control That.

More specifically, it is a method of controlling a mold clamping cylinder for driving the crosshead by using a servo valve.

The mold platen position control device of the toggle type mold clamping device according to the present invention uses the toggle type mold clamping device, injects the molten resin into the mold after completion of the mold clamping, and once the molten resin is solidified. The mold clamping force is released, gas is injected into the molten resin, the movable plate is retracted, and after the molten resin is solidified and cooled, the gas is discharged and the high hollow molded product is taken out from the mold. In a mold plate position control device of a toggle type mold clamping device, a servo valve connected to a mold clamping cylinder of the toggle type mold clamping device, a movable plate retreat speed setter and a movable platen retreat limit position setting connected to the servo valve. A control unit having a container,
A position sensor for measuring the position of the movable plate or the mold, and using the measurement value and the execution value measured by the position sensor the position and speed of the movable plate or the mold, the toggle type mold by the control unit. The configuration is such that the crosshead of the fastening device is feedback-controlled.

More specifically, the control section includes a servo amplifier connected to the servo valve, first and second switches connected to the servo amplifier, the first switch and the movable plate retreat speed setting. A speed feedback controller connected to the controller, a position feedback controller connected to the second switch and the movable platen backward limit position setter, and a comparator connected to each switch and each feedback controller. Is provided, and the speed control and the position control are switched by the comparator and each switch.

The mold platen position control device of the toggle type mold clamping device according to the present invention uses a toggle type mold clamping device having a cross head and a tie bar, and after completion of mold clamping, a molten resin is injected into a mold to melt the molten resin. Before the resin is solidified, the mold clamping force is released, the gas is injected into the molten resin and the movable plate is retracted, and after the molten resin is solidified and cooled, the gas is discharged to form a high hollow molded product from the mold. In a mold plate position control device of a toggle type mold clamping device for controlling to take out, a servo valve connected to a mold clamping cylinder of the toggle type mold clamping device, a movable plate retreat speed setting device connected to the servo valve, and The movable platen is provided with a controller having a backward limit position setter, a crosshead position sensor and a tie bar extension sensor provided in the toggle type mold clamping device, and the movable platen and the movable platen are detected by using detection signals from the respective sensors. A structure in which to perform the control of Rosuheddo.

More specifically, the control unit includes a servo amplifier connected to the servo valve, first and second switches connected to the servo amplifier, the first switch and the movable plate retreat speed setting. A speed feedback controller connected to the controller, a position feedback controller connected to the second switch and the movable platen backward limit position setter, and a comparator connected to each switch and each feedback controller. , The first connected to each of the setters,
A second arithmetic unit is provided, and the speed control and the position control are switched by the comparator and each switch.

[0012]

In the method and apparatus for controlling the mold platen position of the toggle mold clamping device according to the present invention, first, in the case of the constitutions of claims 1 and 4, the injection is carried out after the completion of the mold clamping, and the molten resin is injected at an early stage before the solidification. Retract the crosshead to the crosshead position of to release the mold clamping force. Next, gas injection is started in the molten resin, and the movable plate is retracted at a set speed corresponding to the gas injection amount to form ribs and hollows. Further, the movable platen is retracted at a constant speed by measuring the position with a servo valve for controlling the movement of the crosshead and a movable platen position sensor, and converting the position and time into a velocity for feedback control. When the movable plate retreats to the set position, gas injection is stopped and the position control is switched to cooling until the molten resin solidifies while maintaining that position. When cooling is completed, the gas is discharged. At this time, the tie bar is stretched due to the gas pressure, and if the gas is discharged with the crosshead fixed at that position, the tie bar contracts due to the decrease in the gas pressure. As a result, the movable plate moves forward slightly and the molded product is crushed. However, feedback control of the crosshead is performed to keep the position of the movable plate constant, and until the movable plate reaches the set backward limit position. By controlling the speed and switching to the position control that holds that position when the backward limit position is reached, the distance between the movable platen and the fixed platen during gas discharge can be made constant, and the thickness of the molded product can be kept constant. After that, the mold is opened according to the gas discharge completion signal, and the high hollow molded product is taken out. Further, in the case of the structures of claims 2 and 6, injection is performed after completion of the mold clamping, and the crosshead is retracted to the crosshead position before the injection before the molten resin is solidified to release the mold clamping force. Next, gas injection is started in the molten resin, and the movable plate is retracted at a set speed corresponding to the gas injection amount to form ribs and hollows. Furthermore, since the positional relationship between the crosshead and the movable platen is geometrically determined at this time, the retractable speed of the crosshead corresponding to the retracted speed of the movable platen is calculated, and the position of the crosshead is controlled to control the movable platen. Control the reverse speed of. That is, the movable platen is retracted at a constant speed by measuring the position with a servo valve that controls the movement of the crosshead and a crosshead position sensor, converting the position and time into speed, and performing feedback control. When the movable plate retreats to the set position, gas injection is stopped and the position control is switched to cooling until the molten resin solidifies while maintaining that position. When cooling is completed, the gas is discharged. At this time, the tie bar is stretched due to the gas pressure, and if the gas is discharged with the crosshead fixed at that position, the tie bar contracts due to the decrease in the gas pressure. As a result, the movable plate will move forward slightly and the molded product will be crushed.
The amount of tie bar expansion is measured, and the cross head is retracted in accordance with the contraction of the tie bar, and control is performed to maintain a constant gap between the movable platen and the fixed plate during gas discharge. That is, since the relationship between the amount of extension of the tie bar and the amount of movement of the crosshead is determined by the geometrical calculation of the link mechanism, feedback control of the position of the crosshead that corresponds to the amount of contraction of the tie bar can be performed during gas discharge. It is possible to keep the distance between the movable platen and the fixed platen constant to keep the thickness of the high hollow molded product constant. Further, the mold is opened and the molded product is taken out by the gas discharge signal.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a method and apparatus for controlling a mold platen position of a toggle type mold clamping device according to the present invention will be described in detail below with reference to the drawings. In FIG. 1, a reference numeral 10 is a toggle type mold clamping device. The toggle type mold clamping device 10 includes a tie bar 17 for connecting a fixed plate 11, a movable plate 12 and a housing 13, and a movable plate 12. A plurality of links 18a, 18b, 18c and a crosshead 18d that form a toggle mechanism 18 provided between the housings 13.
And a mold clamping cylinder 20 connected to the crosshead 18d via a piston rod 20b. A fixed mold 14 and a movable mold 15 for forming a cavity 15a are provided between the boards 11 and 12.
A gas pressure source 37 for supplying gas is connected to the cavity 15a via a pressure control device 38.

The movable plate 12 is provided with a position sensor 40 for measuring the position and speed (measurement value and execution value) of the movable plate 12 or the movable mold 15, and the mold clamping cylinder 20. Is connected to a servo valve 35 connected to a hydraulic power source 36, and the servo valve 35 is connected to a servo amplifier 51 of a control unit 60 having a movable platen reverse speed setting device 41 and a movable platen reverse limit position setting device 42. Has been done. This servo amplifier 51 includes the first and second switches 4
9 and 50, and the switches 49 and 50 are connected to the comparator 4
7, the first switch 49 is connected to a speed feedback controller 46 connected to the position sensor 40 via a speed converter 45, and the speed feedback controller 46 moves the movable platen reverse speed setter 41. It is connected to the. The second switch 50 is connected to a feedback controller 48 connected to the movable plate retracting position setting device 42, and the position feedback controller 48 is connected to the position sensor 40.

Next, the operation will be described. Before that,
The main operation of each unit described above will be described. The movable platen retreat speed setter 41 sets the retreat speed of the movable platen 12 during gas injection, and the movable platen retreat limit position setter 42 retreats the movable platen 12 which determines the final thickness of the high hollow molded product 16. The limit position is set, the controllers 46 and 48 compare and control the reverse speed and the set value and the actual value of the reverse limit position, and the comparator 47 and the switches 49 and 50 set the movable platen 12 to the set reverse limit position. The speed is controlled until it reaches, and when it reaches the backward limit position, it is operated to switch to the position control for holding that position. The speed converter 45 described above is not necessary if the speed sensor is provided together with the position sensor 40. The position sensor 40 detects the actual value and performs the following control by using both the set value and the actual value.

First, as is well known using the toggle type mold clamping device 10, after the molds 14 and 15 have been clamped, they are injected from an injection machine (not shown), and the crosshead position before injection is injected at an early stage when the molten resin does not solidify. The cross head 18d is moved backward until the mold clamping force is released. Next, gas injection is started into the molten resin via the gas pressure control device 38, the movable platen 12 is retracted at a set speed corresponding to the gas injection amount, and the cavity 15 is moved.
A rib portion and a hollow portion (not shown) of the high hollow molded product 16 in a are formed. That is, the movable platen 12 is retracted at a constant speed by measuring the position with the servo valve 35 for controlling the movement of the cross head 18d and the position sensor 40, converting the position and time into speed, and performing feedback control. Therefore, at this time, only the first switch 49 is turned on to perform the speed feedback control. When the movable platen 12 retracts to the set position and the position sensor 40 detects that the movable platen 12 has reached the retracted limit position, gas injection is stopped and the output of the comparator 47 switches to the second switch 50. Then, the control is switched to the position feedback controller 48 to perform the position control, and the position is maintained and the molten resin is cooled until it is solidified. When this cooling is completed, the gas is discharged. At this time, the tie bar 17 is expanded due to the gas pressure, and if the gas is discharged while the crosshead 18d is fixed at that position, the tie bar 17 contracts due to the decrease in the gas pressure. As a result, the movable platen 12 moves forward slightly and crushes the high-hollow molded product 16. However, by feedback-controlling the crosshead 18d so as to keep the position of the movable platen 12d constant,
The distance between the movable platen 12d and the fixed platen 11 during gas discharge is kept constant to keep the thickness of the high hollow molded product 16 constant. After that, the mold is opened according to the gas discharge signal and the high hollow molded product is taken out.

Next, in the case of another embodiment shown in FIG. 2, it is basically the same as the first embodiment shown in FIG. 1 except for a part, and the same portions are denoted by the same reference numerals. Only different parts will be described. That is, the housing 13 of the toggle type mold clamping device 10 is provided with the crosshead position sensor 31 for detecting the position of the crosshead 18d, and the tie bar extension sensor 32 for detecting the extension of the tie bar 17 is provided. The position detection signal 31a of the above-mentioned crosshead position sensor 31 is provided to the speed converter 45, the comparator 47 and the position feedback controller 4 of the controller 60.
8 and the extension detection signal 32a of the tie bar extension sensor 32 is input to the position calculator 44 provided between the position feedback controller 48 and the movable platen retreat limit position setter 42, and the speed feedback controller 46 and A speed calculator 43 is provided between the movable platen reverse speed setting device 41.

Next, the operation will be described. Injection is performed after completion of the mold clamping using the toggle type mold clamping device 10, and the crosshead 18d is retracted to the crosshead position before the injection before the molten resin is solidified to release the mold clamping force. next,
Gas injection is started into the molten resin, and the movable plate is retracted at a set speed corresponding to the gas injection amount to form ribs and hollows. At this time, since the positional relationship between the cross head 18d and the movable platen 12 is geometrically determined, the retreat speed of the cross head 18d corresponding to the retreat speed of the movable platen 12 is set to the first computing unit 4
3, the backward speed of the movable platen 12 is controlled by controlling the position of the crosshead 18d. That is, the distance between the movable platen 12 and the fixed platen 11 is measured by measuring the position with the servo valve 35 for controlling the movement of the crosshead 18d and converting the position and time into velocity to perform feedback control. The movable platen 12 is controlled and retracted at a constant speed. When the movable platen 12 retracts to the set position, the gas injection is stopped, the first switch 49 is switched to the second switch 50 to switch to the position control, and the molten resin is cooled while the position is maintained until it solidifies. When cooling is completed, the gas is discharged. At this time, the tie bar 17 is expanded due to the gas pressure, and if the gas is discharged while the crosshead 18d is fixed at that position, the tie bar 17 contracts due to the decrease in the gas pressure.
As a result, the movable platen 12 advances slightly and the high hollow molded product 16
Therefore, the amount of tie bar expansion is measured, and the cross head 18d is retracted by the calculated amount in accordance with the contraction of the tie bar 17, and the distance between the movable platen 12 and the fixed platen 11 during gas discharge is kept constant. To control. Therefore, the relationship between the amount of expansion of the tie bar 17 and the amount of movement of the cross head 18d is determined by the geometrical relation calculation of the link mechanism, so that the cross head 18 corresponding to the amount of contraction of the tie bar 17 is determined.
By performing feedback control of the position of d, the distance between the movable platen and the fixed platen during gas discharge can be made constant, and the thickness of the high hollow molded product 16 can be kept constant.
The mold is opened and the high hollow molded product 16 is taken out. That is, the backward speed control of the movable plate 12 and the holding control at the backward limit position are calculated and controlled by the backward speed and the position of the crosshead 18d, and the deformation amount of the toggle type mold clamping device generated by the gas pressure. Is measured by measuring the amount of change in the elongation of the tie bar 17 and calculating the movement distance of the cross head 18d to control the cross head 18d, thereby controlling the movable plate 12 even if the toggle type mold clamping device 10 is deformed. The distance between the fixed platen 11 and the fixed platen 11 can be controlled so as not to change.

[0019]

Since the method and apparatus for controlling the mold platen position of the toggle type mold clamping device according to the present invention is configured as described above, the following effects can be obtained. That is, since the position of the movable plate or the mold is detected by the position sensor, the speed control is switched to the position control, and the crosshead is feedback-controlled so that the position of the movable plate is always constant.
The movable platen can maintain a constant distance between the fixed plates without being affected by the expansion and contraction of the tie bar, which is expanded by the gas pressure. High quality (the rib and hollow parts are formed as designed). It is possible to obtain a high hollow molded product according to (1). In addition, by equipping the injection molder side outside the mold with the retracting device for the movable mold during gas injection and discharge, instead of inside the mold as in the conventional case, multiple types of molds can be used. Since it does not need to use a mold, it can be provided at low cost. In addition, since the toggle mechanism moves the crosshead in a far greater amount than the moving amount in the movable plate, feedback control of the servo valve is performed at a position where the moving amount is large, so that the movable plate position is smaller than the response accuracy of the servo valve. Since the precision becomes smaller, there is an effect that the precision of the thickness of the molded product is improved, and high quality and high hollow molding can be performed by adding a few devices to a general injection molding machine.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an apparatus to which a mold board position control method of a toggle type mold clamping apparatus according to the present invention is applied.

FIG. 2 is a configuration diagram showing another embodiment of FIG.

[Explanation of symbols]

 10 Toggle Type Clamping Device 11 Fixed Plate 12 Movable Plate 13 Housing 14 Fixed Die 15 Movable Die 16 High Hollow Molded Product 17 Tie Bar 18 Toggle Mechanism 18d Crosshead 20 Die Clamp Cylinder 31 Crosshead Position Sensor 32 Tiebar Extension Sensor 35 Servo Valve 40 Position sensor 41 Movable platen reverse speed setting device 42 Movable platen backward limit position setter 43 Speed calculator 44 Position calculator 45 Speed converter 46 Speed feedback controller 47 Comparator 48 Position feedback controller 49, 50 Switch 51 Servo Amplifier 60 Control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area B29L 22:00

Claims (7)

[Claims] 1. A toggle type mold clamping device (10) is used to inject molten resin into a mold (14, 15) after completion of mold clamping, and release mold clamping force before solidification of the molten resin. Injecting gas into the molten resin and retracting the movable plate (12), discharging the gas after solidifying and cooling the molten resin, and then the mold (14, 15)
The toggle-type mold clamping device is controlled by taking out the high hollow molded product (16) from the machine and using the actual value and the set value obtained by measuring the position and speed of the movable plate (12) or the mold (14, 15). Feedback control of the crosshead (18d) of (10),
Speed control is performed until the movable plate (12) reaches the set backward limit position, and when the movable plate (12) reaches the backward limit position, the movable plate (12) and the fixed plate (11) during gas discharge are switched by switching to position control that holds the position. ) And a constant space between the two) and the platen position control method of the toggle type mold clamping device. 2. A toggle type mold clamping device (10) is used to inject molten resin into a mold (14, 15) after completion of mold clamping, and release mold clamping force before solidification of the molten resin. Injecting gas into the molten resin and retracting the movable plate (12), discharging the gas after solidifying and cooling the molten resin, and then the mold (14, 15)
From the high hollow molded product (16) to control the retreat speed control of the movable plate (12) and the holding control at the retreat limit position by calculating the retreat speed and position of the crosshead (18d). Then, the amount of deformation of the toggle type mold clamping device (10) generated by the gas pressure is calculated as the movement distance of the crosshead by measuring the amount of change in the elongation of the tie bar (17).
It is controlled by controlling (18d) so that the distance between the movable platen (12) and the fixed platen (11) does not change even if the toggle type mold clamping device (10) is deformed. Method for controlling mold plate position of toggle type mold clamping device. 3. The mold of a toggle type mold clamping device according to claim 1, wherein the mold clamping cylinder (20) for driving the crosshead (18d) is controlled by using a servo valve (35). Board position control method. 4. A toggle type mold clamping device (10) is used to inject a molten resin into a mold (14, 15) after completion of mold clamping, and release mold clamping force before solidification of the molten resin. Injecting gas into the molten resin and retracting the movable plate (12), discharging the gas after solidifying and cooling the molten resin, and then the mold (14, 15)
In the mold platen position control device of the toggle type mold clamping device that controls to take out the high hollow molded product (16) from the servo valve (20) connected to the mold clamping cylinder (20) of the toggle type mold clamping device (10). 3
5) and a control unit that is connected to the servo valve (35) and has a movable platen reverse speed setting device (41) and a movable platen reverse limit position setting device (42)
(60) and a position sensor (40) for measuring the position of the movable plate (12) or the mold (14, 15), the movable plate (12) or the mold
The position and speed of (14,15) are measured by the position sensor (40) using the execution value and the set value, and the crosshead (18d) of the toggle type mold clamping device (10) is controlled by the control unit (60). A mold plate position control device for a toggle type mold clamping device, which is configured to perform feedback control. 5. The control unit (60) includes a servo amplifier (51) connected to the servo valve (35), and the servo amplifier (51).
The first and second switches (49, 50) connected to
A speed feedback controller (46) connected to the switch (49) and the movable platen reverse speed setting device (41), and connected to the second switch (50) and the movable platen backward limit position setting device (42). Position feedback controller (48) and each of the above switches
(49, 50) and a comparator (47) connected to each of the feedback controllers (46, 48), the speed control and position control by the comparator (47) and each switch (49, 50). 5. The mold platen position control device for a toggle type mold clamping device according to claim 4, wherein the structure is changed over. 6. A toggle type mold clamping device (10) having a crosshead (18d) and a tie bar (17) is used to inject the molten resin into the molds (14, 15) after the mold clamping is completed, and the melting is performed. Before the resin solidifies, the mold clamping force is released, gas is injected into the molten resin, and the movable plate (12) is retracted to solidify the molten resin.
In the mold platen position control device of the toggle type mold clamping device that controls to discharge the gas after cooling and take out the high hollow molded product (16) from the mold (14, 15), the toggle type mold clamping device ( 1
Servo valve (35) connected to the mold clamping cylinder (20) of (0), and the movable platen reverse speed setting device (41) and movable platen reverse limit position setting device (42) connected to the servo valve (35). A control unit (60) having,
The toggle type mold clamping device (10) is provided with a crosshead position sensor (31) and a tie bar extension sensor (32) provided,
A toggle type mold clamping device characterized in that the movable plate (12) and the crosshead (18d) are controlled by using the detection signals (31a, 32a) from the respective sensors (31, 32). Template position control device. 7. The control unit (60) includes a servo amplifier (51) connected to the servo valve (35), and the servo amplifier (51).
The first and second switches (49, 50) connected to
A speed feedback controller (46) connected to the switch (49) and the movable platen reverse speed setting device (41), and connected to the second switch (50) and the movable platen backward limit position setting device (42). Position feedback controller (48) and each of the above switches
(49, 50) and the comparator (47) connected to the feedback controllers (46, 48), and the first and second computing units (43, 43) connected to the setters (41, 42). 44), and the comparator (47)
7. A mold platen position control device for a toggle type mold clamping device according to claim 6, wherein the switch and the respective switches (49, 50) switch between speed control and position control.