GB2035709A - Platform drive system - Google Patents

Abstract

A stepping drive for generating a linear movement of an elevating platform 4 comprises a rotor 3 which is connected to the stator 1, 2 of the drive via a high-precision thread 6a, 6b by which means a rotation of the rotor produces a corresponding axial displacement of the rotor and of the platform 4. An anti-twisting device 5 is arranged by which means the elevating platform performs only axial movements. The stator has two pole systems (11, 12, Figure 2 not shown) for producing the rotary movement of the rotor. <IMAGE>

Description

SPECIFICATION Platform drive system The invention relates to a drive system for generating a linear movement of an elevating platform, for accurately adjusting the elevating platform to any desired working heightwhich is located between two limits. The invention can be utilised in automatic equipment for semi-conductor production and also in control and servo systems.

In automatic equipment for semi-conductor production, problems of accurate linear adjustment are occurring to an increasing degree. In this type of adjustment it is of advantage to displace the armature in a linear manner in order to save bearing points and to maintain the desired constructional shape.

In order to generate a specified linear movement between two limit positions there are linear motors in which a translatory movement is produced, as is described, for example, in DD-WP 83,200, DE-OS 2,349,139 and US-PS 3,566,224 and 3,851,186. In these the pole systems of the stator are arranged behind one another and act on magnetic projections of the rotor. In this process the frequency pulses are converted directly into incremental path changes.

These arrangements are limited in their accuracy of positioning by the manufacturing accuracy of the pole systems, that is by the modular grid separation of the magnetic projections. It is also of disadvantage in the electro-magnetic linear drive systems that in the rest position they have relatively little rigidity with respect to outside forces in the direction of movement of the system. An electro-magnetic linear drive is unsuitable for driving an elevating platform which is constantly acted upon by outside interferences in the form of variable masses and forces.

In DD-AP 102,248 an electric servo motor is described in which the stepping motor is provided with an axially rigid rotor with a through bore of the rotor shaft. The rotor shaft carries partially an inner thread which co-operates with a threaded spindle. If the rotor is turned a longitudinal displacement of an adjusting member connected to the threaded spindle is effected which is proportional to the rotation of the rotor. In this process the longitudinal movement takes place in very small part-steps. This drive makes use of the combination, known also from many other applications, of a normal rotary stepping motor with a rotatably mounted armature which, however, is axially rigid, and with a threaded spindle/threaded nut system. This produces a relatively complicated construction and a large axial overall size of the system.

In German Offenlegungsschrift 2,720,053 an electro-magnetic stepping motor is described in which the rotor is mounted rotatably on a pivot. This pivot is mounted in the core in such a manner that it is able to slide axially. In this invention there is no correlation between the rotary movement of the rotor and the axial mobility.

From DD-WP 36,236 motors are known which permit a longitudinal displacement of the armature for the purpose of braking or coupling. In this arrangement the armature is moved between two end positions without intermediate stop. The displacement of the armature is here a function for braking which is equalised, for example, in an additional device described in DD-WP 47,230. German Offenlegungsschift 2,115,246 and German Offenlegungsschrift 2,750,843 also describe stepping motors with axial displacement of the rotor for the purpose of coupling or braking.

These inventions do not relate to a specified axial adjustment of the rotor in dependence on the angle of rotation of the rotor.

The object of the invention consists in providing a stepping drive for generating a linear movement of an elevating platform of flat construction, which consists of few components and the movable parts of which have only few bearing points.

It is the task of the invention to obtain, by constructively uniting the transmission system with the motor, preferably a stepping motor, a considerable simplification of the construction by omitting additional bearing points, and also to achieve a flat construction of the stepping motor.

According to the present invention there is provided a drive system for generating a linear movement of an elevating platform comprising a stator (1) having one or several pole systems (2), a rotor (3) mounted so that it is caused to move axially when rotated, the elevating platform being not rotatably mounted with respect to the stator and being connected to the rotor so that axial movement of the rotor causes said linear movement of the elevating platform. In this arrangement the stator effectively engages the rotor via a high-precision thread so that the rotor, when rotated, simultaneously also performs an axial movement. in addition, the outer periphery of the rotor consists of soft-magnetic material and is there provided with teeth and grooves with a constant indexing angle ep.

The pole system or systems are adapted, when driven appropriately, to produce a rotation of the rotor. The pole systems mounted at the stator effectively magnetically engage the teeth of the rotor over the whole traversed.

In addition, between rotor and elevating platform an annular guide is provided which represents a positive effective engagement, with the result that the elevating platform follows the axial displacements of the rotor without play. Between the stator and the elevating platform also an anti-twisting device is arranged.

In develeopement of the invention, a pole system consists of two pairs of poles with two single poles each. The single poles also carry teeth, the teeth of the first single pole of the first pair of poles in an assumed basic position overlapping the teeth of the rotor and the teeth of the second single pole being provided with an offset of 112cup, the teeth of the first single pole of the second pair of poles with an offset of 3/4 qo and the teeth of the second single pole with an offset of l/4s with respect to the teeth of the rotor.

Between the two pairs of poles also a permanent magnet is arranged.

In further development of the invention the stator is provided with two pole systems.

In further development the height of the pole systems is greater than or equal to the length of the traverse d plus the height of the teeth of the rotor.

In further development of the invention the stator carries a guide pivot which at its lower end is provided with the high-precision outer thread, the rotor having a centric bore with the high-precision inner thread. The guide pivot carries at its upper end a sliding block as anti-twisting guard between stator and elevating platform. In this arrangement the sliding block engages an axial groove of the elevating platform.

Reference is now made to the accompanying drawings, in which: Figure 1 shows the section A-A through the illustrative embodiment, and Figure 2 shows the electromagnetic pole system.

The stepping drive, shown in Figure 1, for generating a linear movement of an elevating platform is constructed predominantly rotationally symmetrically and consists of a stator 1 with a pole system 2, a rotor 3 which can be turned with respect to the stator 1 and thus also moves axially, and an elevating platform 4 with an anti-twisting device 5.

In this arrangement the stator 1, here constructed in the shape of a disc, carries an edge projection 25 for attaching the pole system 2, and a centric guide pivot 22. The guide pivot 22 carries at its lower end a high-precision outer thread 6a and at its upper end the anti-twisting device 5 in the form of a sliding block. The rotor 3 is also constructed as a flat plate which carries in a centric bore 23 the corresponding high-precision inner thread 6b which effectively engages the high-precision outerthread 6a. In addition, the outer periphery of the rotor 3 consists of soft-magnetic material and is there provided with teeth 7 and grooves 8 with a constant indexing angle cp. The pole system 2 consists of two pairs of poles 11; 12 with the single poles 13; 14; 15; 16.The single poles 13; 14; 15; 16 each carry teeth 17; 18; 19; 20 which effectively engage the teeth 7 magnetically over the whole traversed. In this arrangement the height of the pole system is greater than or equal to the length of the traverse d plus the height of the teeth 7.

In an assumed basic position the teeth 17 overlap the teeth 7 and the teeth 18 are provided with an offset of 1/2rip, the teeth 19 with an offset of 3/4(p and the teeth 20 with an offset of 1/4cp with respect to the teeth 7. In addition, between the pairs of poles 11; 12 a permanent magnet 21 is arranged.

If the individual poles 13; 14; 15; 16 are driven in a suitable manner the pole system 2 is adapted to produce a rotation of the rotor 3. The rotor 3 thereby moves along the high-precision thread 6 in the axial direction with respect to the stator 1. In addition, the rotor 3 is provided with an annular guide 9 and the elevating platform 4with a corresponding guide 10.

The guides 9; 10 engage one another effectively positively and without play, as a result of which the elevating platform 4 also performs the axial movement of the rotor 3. The anti-twisting device 5, which is free of play, arranged at the upper end of the guide pivot 22 engages an axial groove 24 of the elevating platform 4. This fixes the angular position of the elevating platform 4 with respect to stator 1 and the elevating platform 4 performs the axial movements transmitted by the rotor 3.

In the embodiment according to the invention it is furthermore of advantage that the torque of the rotor 3, and thus the lifting force of the elevating platform 4, change linearly with the diameter of the rotor 3. In addition, the flat construction is advantageous during use. In addition, it is possible to provide the plate of the rotor 3 with perforations in orderto realise a low moment of inertia while retaining adequate rigidity.

Claims (1)

1. A drive system for generating a linear movement of an elevating platform comprising a stator (1) having one or several pole systems (2), a rotor (3) mounted so that it is caused to move axially when rotated, the elevating platform being not rotatably mounted with respect to the stator and being connected to the toyor so that axial movement of the rotor causes said linear movement of the elevating platform.

2. A system according to Claim 1 wherein the rotor (3) is screw threadedly mounted on the stator (1) via a high-precision screw thread (6).

3. A system according to Claim 1 or 2 wherein the outer periphery of the rotor (3) consists of a soft magnetic material and is provided with teeth (7) and grooves (8) spaced to provide a constant indexing angle cp, the pole systems (2) magnetically cooperating with the teeth (7) over the whole axial traverse (d) and are adapted to produce rotation of the rotor.

4. A system according to Claim 1,2 or 3 wherein the rotor is provided with an annular groove (9) and the platform is provided with an annular projection (10) which is located within groove (9) so that the rotor and platform are axially movable in unison, anti rotation means (5) being provided to prevent the platform rotating relative to the stator 5.A system according to any of Claims 1 to 4, characterised in that a pole system (2) consists of two pairs of poles (11 ;12) with the single poles (13;14;15;16), that the single poles (13;14;15;16) each carry teeth (17;18;19;20)which effectively engage the teeth (7) magnetically, the teeth (17), in an assumed basic position, overlapping the teeth (7), and that the teeth (18) are provided with an offset of 1/2rep, the teeth (19) with an offset of 314up and the teeth (20) with an offset of 1/4cup with respect to the teeth (7), and that between the pair of poles (11) and the pair of poles (12) a permanent magnet (21) is arranged.

6. A system according to any of Claims 1 to 5, characterised in that the stator (1) is provided with two pole systems (2) is greater than or equal to the length of the traverse (d) plus the height of the teeth (7).

8. A system according to Claim 2 or any of Claims 3 to 7 when dependent on Claim 2 characterised in that the stator (1) carries a guide pivot (22) which at its lower end is provided with the high precision outer thread (6a), that the rotor (3) is provided with a central bore (23) with a highprecision inner thread (6b), and that the guide pivot (22) at its upper end carries a sliding block as anti-rotating device (5) which engages an axial groove (24) in the elevating platform (4).

9. A drive system for generating a linear movement of an elevating platform substantially as described with reference to and as illustrated in the accompanying drawings.