WO2003046388A1

WO2003046388A1 - Actuator

Info

Publication number: WO2003046388A1
Application number: PCT/EP2002/013472
Authority: WO
Inventors: Eckhard Polman
Original assignee: Eckhard Polman
Priority date: 2001-11-26
Filing date: 2002-11-26
Publication date: 2003-06-05
Also published as: DE20119153U1; AU2002358057A1

Abstract

The present invention relates to an actuator (1) having a housing (1a) in which a driving shaft (2) is accommodated provided with a through bore (7), which through bore serves as an actuated cylinder (3), at least one piston (4) and a piston shaft (5) extending axially in said through bore, said at least one piston and said piston shaft being rotatable together with said driving shaft. Based on the known prior art, it is the aim of the invention to provide an improved actuator according to the above preamble, which obviates the described drawbacks, and which allows an accurate and stable positioning of the piston shaft in axial direction. As a technical solution for this object the actuator according to the invention is characterised in that said at least one piston and said piston shaft is movable back and forth in both directions within said through bore by actuating said cylinder. This allows an accurate positioning of the piston shaft relative to the driving shaft enabling the accurate operation of the actuator under various operating conditions.

Description

Actuator.

DESCRIPTION

The present invention relates to an actuator having a housing in which a driving shaft is accommodated provided with a through bore, which through bore serves as an actuated cylinder, at least one piston and a piston shaft extending axially in said through bore, said at least one piston and said piston shaft being rotatable together with said driving shaft.

Such actuators are known in the state of the art and are used for driving all kinds of devices, which devices are intended to perform besides a rotational movement also an axial movement for adjusting purposes. Therefore such devices are fixed to an end of said piston shaft projecting out of said shaft of the actuator, which piston shaft extends axially into a through bore in said shaft and is can be rotated together with said shaft. Thus said device can be rotated and displaced in axial direction together with the axially extending piston shaft. From DE-19647396 it is disclosed to use such an actuator as driving means of a measuring device of an underwater pelletizer. The measuring device is to be considered as the device to be used with the actuator according to the present invention. Furthermore, such actuators are for example used for setting transmission devices as well as for coupling or shaft exchangers.

A drawback of the known actuators is, that an accurate and stable position of the piston shaft in axial direction can not be maintained. It can happen that the axial position of the piston shaft in certain operation conditions, for example due to forces exerted in axial direction on said device, changes. These uncommon and undesired displacements result in an increased wear and damages to the device, as well as a reduced accuracy of the operations to be performed with said devi ce.

Based on the known prior art, it is the aim of the invention to provide an improved actuator according to the above preamble, which obviates the described drawbacks, and which allows an accurate and stable positioning of the piston shaft in axial direction.

As a technical solution for this object the actuator according to the invention is characterised in that said at least one piston and said piston shaft is movable back and forth in both directions within said through bore by actuating said cylinder. This allows an accurate positioning of the piston shaft relative to the driving shaft enabling the accurate operation of the actuator under various operating conditions.

According to a further preferred embodiment of the invention the position of the piston shaft relative to the shaft is controllable, preferably using actuating and control means. This improves the accurate operation of the actuator according to the invention as external influences on the position of the piston shaft, e.g. forces exerted in axial direction on said piston shaft, are now minimized and corrected. This also reduces wear and inaccuracy of the actuator, extending its life span as furthermore an automatic correction of the position within the framework of the control is herewith obtained.

In a preferred embodiment of the invention the actuated cylinder is a double-acting piston cylinder.

According to the invention, also a cylinder with several pistons (multiple piston cylinder) is applicable.

In another preferred embodiment the actuator according to the invention is provided with locking means interacting with the piston shaft, which locking means lock the axial position of the piston shaft relative to the shaft. Using the preferably pneumatic operatable locking means an accurate and stable positioning of the piston shaft in axial direction is obtained. In a further embodiment of the invention the force for locking the axial position of the piston shaft is approximately two till three times the displacement force of the cylinder, thus allowing an reliable locking of the piston shaft under all possible operating conditions.

In a preferred embodiment of the invention the locking means comprise at least one ring-shaped element, which element at least partly surrounds the piston shaft, and which ring-shaped element interacts with the piston shaft by means of a pneumatic actuated lever, preferably a so called knee lever, for locking the piston shaft in a desired position relative to the shaft. By operating the lever, the ring shaped element will be urged or pressed against the piston shaft thus locking or blocking the piston shaft in a mechanical manner.

In a further embodiment of the invention the ring shaped element is a ring surrounding the piston shaft, preferably a stainless ring.

According to a further preferred embodiment of the invention the actuator is provided with measuring means for determining the position of the piston shaft, which measuring means are preferably adapted for determining the axial position of the piston shaft with an accuracy of one tenth of a millimetre. Preferably it is possible to lock the piston shaft with the locking means in its axial position relative to the shaft with an accuracy of one tenth of a millimetre.

According to a further preferred embodiment of the invention the position of the piston shaft relative to the shaft is controllable, preferably using actuating and control means connected with the pneumatic cylinder, the locking means and the measuring means. The piston shaft is preferably movable in both directions

In a further embodiment of the invention the measuring means are provided integrally with the locking means, such that they are constructed as one unit. Such a unit can easily be replaced, for example in the event of a malfunction. Accordingly, it is also without effort possible to adapt an ordinary actuator with the features according to the invention.

In a further preferred embodiment of the invention the measuring means are mounted on the actuator. In a further preferred embodiment of the invention the measuring means are mounted at an universal joint for the pneumatic supply of the cylinders and/or the locking means.

In a specific embodiment said measuring means comprise a magnet positioned on said piston shaft, which magnet is movable accommodated through one or more electromagnetic coils placed around said piston shaft. Thereby operate the measuring means according to the principle of electro-magnetic induction (LVDT-principle) . This ensures an accurate and contactless measurement of the position of the piston shaft.

In a preferred embodiment of the invention the actuator is used as driving means of a pelletizer, in particular an underwater pelletizer.

In a further embodiment the actuator is used as driving means of a transmission setting device.

According to a further embodiment the actuator is used as driving means of a coupling- or a shaft exchanger.

Moreover the actuator can be an electro- or pneumatic motor, whereas the cylinder can be an pneumatic, hydraulic or electronic actuated cylinder.

Further advantageous characteristics of the invention are described below using the preferred embodiments shown in the drawing, which drawing shows in:

Figure 1 a first embodiment of an actuator according to the invention;

Figure 2 a second embodiment of an actuator according to the invention;

Figure 3 a third embodiment of an actuator according to the invention; Figure 4 and 5 detailed views of another embodiments of an actuator according to the invention.

Figure 1 shows a partly open side view of a first embodiment of an actuator 1 according to the invention. The actuator can be constructed as an electromotor, e.g. an AC electromotor or as an hydraulic or pneumatic motor. The actuator has a housing la in which a driving shaft 2 is accommodated. Said driving shaft 2 of the actuator 1 is provided with an axial through bore 7 with a significant cross section, in which a piston shaft 5 is accommodated. The cross section of the axial through bore 7 corresponds with the cross section of the piston shaft 5. The piston shaft 5 is mounted axially in a liquid tight manner in the through bore 7 and is made of stainless steel and projects with its free end 5a (left side in the drawing) out of the shaft 2. To this free end of the piston shaft 5 a desired device to be driven is mounted. Furthermore in said housing la a cylinder 3 is present, wherein the cylinder wall 3a forming said cylinder 3 is connected to the driving shaft 2. Said driving shaft 2 with the cylinder housing 3a is rotatable accommodated in said housing la by means of suitable ball bearings 13a and 13b. In said cylinder 3 a piston 4 is accommodated, which piston is connected or mounted to the piston shaft 5.

The piston shaft 5 as well as the piston 4 can be rotated together with the driving shaft 2, whereas the piston shaft 5 and the piston 4 furthermore can be displaced in axial direction through the shaft 2 due the actuation of the cylinder 3. As clearly shown in Figure 1 the piston 4 divides the cylinder 3 in two chambers 17a-17b, wherein each cylinder chamber 17a-17b is connected with supply line 10 or 12 respectively. The piston 3 is connected via an universal joint 11 to supply lines 10 and 12 for supplying pressurised air or another pneumatic or hydraulic medium to the two chambers piston 4 for displacing the piston 4 within the cylinder 3 and thus the piston shaft 5 within the through bore 7 of the shaft 2. The supply lines 10 and 12 of the universal joint 11 are connected to an actuating and control means (not shown) for actuating the cylinder 3 and for controlling the movements of the piston shaft 5 and piston 4 within the cylinder 3 and the shaft 2.

The actuation and displacement of the piston 4 within the cylinder 3 takes place by creating a pressure difference between the two cylinder chambers 17a-17b in order to displace the piston 4 and thus the piston shaft 2 in axial direction. The actuation and control means (not shown) can be operated as a hydro-pneumatic control means in order to control the position of the piston shaft 5 relative to the driving shaft 2. The position of the piston 4 within the cylinder 3 can be maintained by for example equalizing the pressure difference between both cylinder chambers 17a-17b by opening a valve between both supply lines 10-12.

Thus with the use of pressure differences it is with this embodiment possible to displace the piston shaft 5 back and forth in both directions within the shaft 2 enabling the accurate operation of the actuator under various operating conditions.

As the position of the piston shaft 5 relative to the shaft

2 is controllable using said actuating and control means the accurate operation of the actuator 1 is herewith improved as external influences on the position of the piston shaft 5, e.g. forces exerted in axial direction on said piston shaft 5, are now minimized and corrected. This also reduces wear and inaccuracy of the actuator 1, extending its life span as furthermore an automatic correction of the position of the piston shaft 5 and the device to be driven connected to said piston shaft 5 is obtained.

Figure 2 shows a partly open side view of an actuator 1, here an AC electromotor. Also in this embodiment the corresponding parts are denoted with the same reference numerals. The driving shaft 2 of the actuator 1 is provided with an axial through bore 7 with a significant cross section. The through bore 7 serves as a pneumatic actuated cylinder

3 in which a piston 4 and a piston shaft 5 is disposed. The piston shaft 5 can be displaced in axial direction through the shaft 2 as well as rotated together with the shaft 2. The cross section of the axial through bore 7 corresponds with the cross section of the piston 4 and the piston shaft 5 of the cylinder 3.

In a similar manner in conjunction with Figure 1 the piston 4 can be displaced within the through bore 7 by applying pressure differences via said pneumatic or hydraulic supply lines 10-12 to the cylinder chambers present at both sides of the piston 4 within the through bore 7/cylinder 3.

The piston shaft 5 is mounted axially in a liquid tight manner in the through bore 7 and is made of stainless steel and projects with its free end (left side in the drawing) out of the shaft 2. To this free end of the piston shaft 5 a desired device to be driven is mounted. During operation the piston shaft 5 of the cylinder 3 moves over specific distances in and out the shaft 2 of the actuator 1, as shown in the drawings with the double arrow V.

Locking means 6 for locking or fixating the axial position of the piston shaft 5 relative to the shaft 2 are mounted near the other end of the piston shaft 5 (right side of the drawing). In another embodiment (not shown) the locking means are connected to the actuator and rotate with it during operation. The locking means 6 comprise a ring 8 manufactured from steel, through which ring 8 the piston shaft 5 of the cylinder 3 is guided, and wherein the ring 8 can be urged against the piston shaft 5 of the cylinder 3 using a pneumatic actuated knee lever 9 in order to lock or fixate the piston shaft 5. Near the end (right side of the drawing) an universal joint

11 with a connection for pressurised air is mounted to the fixation means 6, for supplying pressurised air or another pneumatic medium to the piston 4 for displacing the piston shaft 5 within the cylinder 3. The supply for pressurised air 10 of the locking means 6 and the supply of pressurised air 12 of the universal joint 11 of the piston 4 of the cylinder 3 are connected to an actuating and control means (not shown), for actuating and controlling the movements of the piston shaft 5 and piston 4 within the cylinder 3 and the shaft 2 as well as the lever 9 of the locking means 6 in a predetermined manner, such that the force for locking the actual position of the piston shaft 5 will be two till three times larger as the friction force of the cylinder 3. The position of the piston shaft 5 relative to the shaft 2 is obtained with an accuracy of one tenth of a millimetre using a measuring device 13 integrally mounted to the locking means 6, which position is passed as a further control value to the actuating and control means. The axial position of the piston shaft 5 relative to the shaft 2 can be locked by the locking means 6 with an accuracy of one tenth of a millimetre using the driving and control means.

In Figure 3 a further embodiment of an actuator according to the invention is shown, which embodiment comprises a multiple-piston cylinder consisting of multiple pistons 4 mounted on the piston shaft 5, dividing the cylinder 3 in separate cylinder chambers.

In Figure 4 a detail is shown of the free end 5a of the piston shaft 5 extending from the housing la of the actuator 1. According to another aspect of the invention the free end 5a is provided with a coupling element 21, which coupling element 21 serves as a mounting element for a device to be actuated by the actuator. The coupling element 21 is mounted in a fixed manner to the free end 5a of the piston shaft 5, e.g. by means of a press fit.

The coupling element 21 is also mounted with its flange 21a to the end 2a of the driving shaft 2 by means of several ball splines 20. The ball splines 20 comprises several splines or grooves 20a-20c provided in the circumferential surface of the free end 2a of the shaft 2 respectively the inner circumferential surface 22 of the flange 21a of the coupling element 21. In said coinciding grooves or splines 20a-20c iron balls are placed. The ball spline 20 ensures a rotational fixation of the piston shaft 5, the coupling element 21 and the driving shaft 2, whereas the ball spline also allows an axial displacement of the coupling element 21 (together with the device mounted to it) due to the actuation of the cylinder 3 and the displacement of the piston shaft 5.

The coupling element 20 can be regarded as an universal mounting tool for all kinds of devices, which have to be driven/actuated with the actuator according to the invention. A further detail is shown in Figure 5 showing the measuring device mounted to the piston shaft 2. The measuring device comprises a magnet 25 placed in the piston shaft 2a. Outside and adjacent to the piston shaft 2a measuring coils 25a-25b are placed, which measure the axial displacement of the piston shaft 2-2a by means of electro-magnetic induction. More in particular the measuring device uses the LVDT- principle.

The piston shaft 2a is only capable of axial displacement as the shaft 2a is connected with the actual piston shaft 2 by means of a ball bearing coupling 23a-23b. The embodiments shown in the drawings serve only as an elucidation of the invention and does not limit the invention.

Claims

1. An actuator comprising: a housing in which a driving shaft is accommodated provided with a through bore, which through bore serves as an actuated cylinder, at least one piston and a piston shaft extending axially in said through bore, said at least one piston and said piston shaft being rotatable together with said driving shaft, characterized in that said at least one piston and said piston shaft is movable back and forth within said through bore by actuating said cylinder.

2. An actuator according to claim 1, characterized in that said cylinder is a double-acting cylinder.

3. An actuator according to claim 1, characterized in that said cylinder is a multiple piston-cylinder.

4. An actuator according to anyone of the preceding claims, characterized in that said cylinder is a pneumatic, hydraulic or electronic actuated cylinder.

5. An actuator according to anyone of the preceding claims, characterized in that the cylinder is actuated using actuating and control means, which serve as hydro-pneumatic control means.

6. An actuator according to anyone of the preceding claims, characterized in that it comprises locking means interacting with the piston shaft, which locking means lock the axial position of the piston shaft relative to the shaft.

7. An actuator according to claim 6, characterized in that the force for locking the axial position of the piston shaft is approximately two till three times the displacement force of the cylinder.

8. An actuator according to claim 6 or 7, characterized in that, the locking means comprise at least one ring-shaped element, which element at least partly surrounds the piston shaft, and which ring-shaped element interacts with the piston shaft by means of a pneumatic actuated lever for locking the piston shaft in a desired position relative to the shaft.

9. An actuator according to claim 8, characterized in that the ring shaped element is a ring surrounding the piston shaft, preferably a stainless ring.

10. An actuator according to anyone of the claim 6-9, characterized in that the locking means are capable of locking the piston shaft in its axial position relative to the shaft with an accuracy of one tenth of a millimetre.

11. An actuator according to anyone of the preceding claims, characterized in that the actuator is provided with measuring means for determining the axial position of the piston shaft.

12. An actuator according to claim 11, characterized in that the measuring means are adapted for determining the axial position of the piston shaft with an accuracy of one tenth of a millimetre.

13. An actuator according to claim 11 or 12, characterized in that the measured axial position of the piston shaft serves as a control value for actuating and control means of the cylinder.

14. An actuator according to anyone of the claim 11-13, characterized in that said measuring means comprise a magnet positioned on said piston shaft, which magnet is movable accommodated through one or more electromagnetic coils placed around said piston shaft.

15. An actuator according to anyone of the preceding claims, characterized in that the free end of the piston shaft is provided with a coupling element for mounting all kinds of devices.

16. An actuator according to claim 15, characterized in that the coupling element is connected with the free end of the driving shaft by means of at least one ball spline.