GB2521912A

GB2521912A - Motorised drive unit for a microscope table

Info

Publication number: GB2521912A
Application number: GB1419550.7A
Authority: GB
Inventors: Ralf Tide; Martin Volk
Original assignee: Marzhauser Wetzlar GmbH and Co KG; Maerzhaeuser Wetzlar GmbH and Co KG
Current assignee: Marzhauser Wetzlar GmbH and Co KG; Maerzhaeuser Wetzlar GmbH and Co KG
Priority date: 2013-11-19
Filing date: 2014-10-31
Publication date: 2015-07-08
Anticipated expiration: 2034-10-31
Also published as: GB201419550D0; GB2521912B

Abstract

A motorised drive unit for adjusting a microscope table. The drive unit comprises a drive shaft 3 on which is arranged a rolling ring transmission 5, which comprises a carrier and three rings 6 which contact and surround the shaft. The rings are inclined to the axis, with the outer rings having inclinations parallel to one another. The inner ring is inclined at the same angle but in an opposite direction. The inside surface 8 of each ring comprises two faces meeting one another at an angle. In use, one face acts against the shaft via friction, and the other is inclined to it. The shaft is rotated by an electric motor 1, which causes the rolling ring transmission to transverse the shaft. A screw 11 and a resilient washer act upon a bearing mount of the centre ring, to cause the rings to clamp against the shaft.

Description

MOTORISED DRIVE UNIT FOR A MICROSCOPE TABLE

The present invention relates to a motorised drive unit for a microscope table.

Microscope tables with motorised table adjustment are known in various forms.

Microscope tables usually consist of two table plates which are disposed one above the other and are mounted perpendicularly with respect to one another on a stationary base plate to be displaceable. Usually provided as drive units are electric motors which drive, by way of a coupling, a spindle on which a nut connected with the table plate is mounted.

The motor housings have a predetermined size. The diameters of the spindle and the nut are dependent on the required stability, the length of the travel paths of the tables and the required positioning accuracy. The last-mentioned is dependent on the pitch of the thread on the spindle. The spindle is, in general, separately mounted and has to be adjusted for alignment with the motor axis.

In the case of a motorised table drive known, from DE 10 2004 057 451 Al the height dimensions of the drive housing considerably exceed the thickness of the table plates, wherein one drive unit is arranged laterally above and the other perpendicularly thereto below the table. The housings, which project beyond the table plate, of the drive units obstruct manipulation of objects on the microscope table.

A microscope table is known from US D596 655 5 in which two drive housings are recessed relative to the table surface so that free access to the table surface from all sides is given.

Common to all prior art constructions are the relatively high overall superstructures of the microscope tables with motorised table adjustment. The mechanically positive coupling of the drive units with the table plates to be adjusted produces a risk of jamming in mutually adjustable openings of the table surfaces.

Currently available high-performance electric motors are known in comparatively compact forms. However, the spindle drives cannot be reduced in constructional size to such an extent as may be desired, so that the constructional heights of the drive units again exceed the table heights.

Apart from spindle drives, a friction transmission is known from DE 1 057 411, which has, instead of a spindle, a smooth shaft and a linear drive nut' consisting of several rolling rings. Due to the inclined setting of the rolling rings relative to the shaft they act like the nut of a screw spindle. The internal running surface of each of the rolling rings is formed with a spherical convexity. The diameter of the shaft and the size of a housing of the linear drive nut in known constructions are designed for robust industrial app'ications and are not suitable for incorporation in microscope tables with high demands on positioning accuracy.

The invention therefore has the object of creating a motorised drive unit for microscope tables, which drive unit can be integrated in the constructional height of the table construction and prevents risk of jamming curing table adjustment.

According to the present invention this object is fulfilled in the case of a microscope table with a motorised table adjustment in that an electric motor with a drive shaft with constant or continuous extension at one end and a rolling ring linear drive or transmission arranged thereon are present as drive unit.

It has unexpectedly proved that electric motors of small mode of construction may be capable of directly driving a transmission element, particularly a linear drive nut, i.e. rolling ring transmission, if an extended or prolonged drive shaft is provided. The arrangement of the linear drive nut on the extended drive shaft saves separate mounting of the linear drive nut shaft and connection of the shaft by way of a coupling. Adjustment of the running axis for the linear drive nut in conjunction with the microscope table to be driven is substantially simplified. The drive unit as a whole can be significantly more compact than prior art drive units.

Construction of the inner or internal running surface as a symmetrical pointed cone is particularly advantageous for play-free frictional mounting of rolling rings of the transmission on the drive shaft, which is smooth. It has proved that the cone point resting under pressure on the drive shaft does not produce corrugations such as might prevent smooth running of the linear drive nut. Even after multiple back-and-forth running of the rolling rings due to reversal of the rotational direction of the drive shaft no damage of the preferably hardened and polished surface of the drive shaft can be seen.

The length of the drive shaft can be adapted to usual table adjustment ranges of 100 to millimetres and has proved to be very load-bearing capable in the case of a free length of approximately 150 millimetres.

The rate of advance of the linear drive nut is dependent in known manner on the rotational speed of the drive shaft and the inclination of the rolling rings with respect to the axis of the drive shaft, With respect to the matching of the two parameters, an angle of incidence of 3° to 12°, particularly 4.5°, has proved advantageous for the required positioning accuracy and position repeatability.

For selling of the appropriate angle of incidence and for insertion of the drive shaft it has proved advantageous if the diameter of the frictional contact of each of the rolling rings is 0.4 to 0.8 millimetres, particularly 0.5 millimetres1 greater than the diameter of the drive shaft. By virtue of the pointed-cone construction of the frictional contact surface, different adjustment speeds can be set in wide ranges even with this small difference in diameter, For installation in a microscope table small electric motors with a drive shaft diameter of 4 to 6 millimetres have proved particularly advantageous. The free end of the extended drive shaft is advantageously supported in a bearing which can also accept small transverse displacements of the drive shaft.

A linear drive nut' preferably consists of three rolling rings, wherein the inclinations of the two outer rolling rings with respect to the axis of the drive shaft are parallel to one another and the inclination of the centre rolling ring is arranged with the same1 but oppositely directed, angle of inclination. In that case the frictional contact zone of the two outer rings lies on one side of the drive shaft and the frictional contact zone of the centre rolling ring lies on the side of the surface of the drive shaft opposite thereto. Due to pressure on the centre rolling ring perpendicularly to the axis of the drive shaft a symmetrical bracing of the rolling rings at the drive shaft is produced. The pressure determines on the one hand freedom of the linear drive nut from slip and on the other hand, in dependence thereon, the friction force, which is to be overcome, for clamping protection.

Miniaturisation of the rolLing ring transmission is achieved through arrangement of the rolling rings in bearing mounts with suitable contact surfaces and incorporation of the bearing mounts in a common carrier. In that case, the bearing mounts for the two outer rolling rings are fixed in the carrier and the bearing mount of the centre rolling ring is arranged to be adjustable in height and laterally in the carrier. After assembly, the openings of the rolling rings lie in a row one behind the other so that the drive shaft can be pushed through. The rotational axes of the roiling rings lie in a common plane together with the axis of the drive shaft. The centre bearing mount is adjustable perpendicularly to the axis of the drive shaft in the carrier by lateral pressure. As a result, the rolling rings come into punctiform contact with the drive shaft. On change in the contact pressure, the contact points of the outer and centre rolling rings shift diametrally with respect to one another on the circumferential surface of the drive shaft.

For changing the contact pressure of the rolling rings a grub or set screw is arranged in the carrier and advantageously acts on the bearing mount by way of a resilient washer. On installation of the rolling ring transmission in a microscope table the frame is advantageously aligned so that the screw is accessible from an open side.

For precise positioning of the microscope table independently of the set pressing pressure it is advantageous if a position measuring system with a linear measuring scale and control means for a regulating circuit is associated with the table adjustment. The drive unit can then be controlled in a manner known per se in dependence on the position measurement signals.

A preferred embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross-sectional view of a drive unit embodying the invention and Fig. 2 is a schematic perspective view from above of the drive unit.

Referring now to the drawings, Fig. 1 shows a drive unit comprising an electric motor 1 with electrical terminals 2 and a drive shaft 3 continuously prolonged at one end and of substantially constant diameter. The drive shaft 3 is mounted, in alignment with the motor axis, at a free end in a mount 4 with a play perpendicularly to the drive shaft 3. A rolling ring transmission 5 is pushed onto the drive shaft 3. The drive shaft 3 has, for example, a diameter of 4 millimetres and the surface thereof is ground.

The rolling ring transmission 5 consists of three rolling rings 6, which are each arranged in a respective bearing mount 7 at an angle of 9° relative to one another and symmetrically at an angle of 4.5° with respect to the axis of the drive shaft 3. The internal running surface 8, i.e. inner circumferential surface, of the rolling ring 6 is ground to be of symmetrical pointed-cone form. The angle of the pointed cone is selected so that an unobstructed inclination relative to the drive shaft 3 over a range of 3° to 12° is possible. In the illustrated orientation of Fig. 1 the two outer rolling rings 6 bear from above against the drive shaft 3 and the centre rolling ring 6 from below. Through symmetrical bracing of the rolling rings 6 relative to one another the contact zones of the pointed-cone running surfaces 8 do not lie in the same sectional plane, i.e. one of the two annular chamfers defining the pointed conical form has maximum frictional contact with the shaft at one side thereof and the other one of the chamfers has maximum frictional contact with the shaft at the opposite side thereof as can be inferred from Fig. 1. The opening diameter (cone base diameter) of the pointed-cone running surfaces 8 is approximately 0.5 millimetres greater than the diameter of the drive shaft 3. That makes it possible to easily push the rolling ring transmission 5 onto the drive shaft 3 when the rolling rings 6 are not braced relative to one another.

As shown in the perspective view of the drive unit, the rolling rings 6 are held in a common carrier 9. The bearing mounts 7 of the two outer rings 6 are fastened in stationary position in the carrier 7. The bearing mount 7 of the centre rolling ring 6 is arranged in the carrier 9 to be displaceable both in height and laterally, as can be seen at the gap 10 between the bearing mount 7 and the carrier 9.

A grub or set screw 11, which is not illustrated in detail, is inserted into the carrier 9 and when screwed in acts on the bearing mount 7 of the centre rolling ring 6. A resilient washer, which is not illustrated in detail, is inserted between a head of the screw 11 and the bearing mount 7 so that the bracing or pressure of the rolling ring 6 against the drive shaft 3 loosens or reduces when a predetermined resistance is reached during displacement of the rolling ring transmission 5 and the drive shaft 3 can further rotate without axial movement or advance of the rolling ring transmission 5. A settable clamping protection is achieved in this way Fastened to the carrier 9 is a flange 12 which can be coupled with a microscope table (not shown). For precise positioning of the microscope table a position measuring system with linear measuring scale and regulating-circuit control is associated in a manner known per se with the drive unit. Thus, slipping as a consequence of the clamping protection does not have a disadvantageous effect on the positioning of the microscope table.

Claims

CLAIMS1. A motorised drive unit for a microscope table, comprising an electric motor with a drive shaft, which has a constant extension at one end, and a rolling ring transmission arranged on the drive shaft extension.
2. A drive unit according to claim 1, wherein the rolling rings each have a symmetrical pointed-cone internal annular running surface.
3. A drive unit according to claim I or claim 2, wherein the free length of the drive shaft is between 100 and 200 millimetres.
4. A drive unit according to claim 3, wherein the free length is substantially 150 millimetres.
5. A drive unit according to any one of the preceding claims wherein the rolling rings each have an inclination relative to the axis of the drive shaft of 3° to 12°,
6. A drive unit according to claim 5, wherein the inclination is substantially 4.5°.
7. A drive unit according to any one of the preceding claims, wherein the diameter of the annular running surface of each the rolling rings is 0.4 to 0.8 millimetres greater than the diameter of the drive shaft.
8. A drive unit according to claim 7, wherein the diameter of the annular running surface of each of the rolling rings is substantially 0.5 millimetres greater than the diameter of the drive shaft.
9. A drive unit according to any one of the preceding claims, wherein the diameter of the drive shaft is preferably 4 to 6 millimetres.
10. A drive unit according to any one of the preceding claims, wherein the rolling ring transmission consists of three rolling rings, the two outer ones of which are arranged in stationary position and the centre one of which is arranged to be displaceable in height and laterally in bearing mounts of a common carrier of the rings.
11. A drive unit according to any one of the preceding claims, comprising a position measuring system with linear measuring scale for measuring table adjustment by the drive unit.
12. A drive unit according to any one of the preceding claims, wherein the drive shaft has a free end supported in a mount in alignment with the motor axis.
13. A drive unit according to any one of the preceding claims, wherein the surface of the drive shaft is hardened, polished or ground.
14. A drive unit according to any one of the preceding claims, wherein the transmission comprises a rolling ring carrier equipped with a magnet or light-barrier switching vanes to trigger table end adjustment positions by the drive unit.
15. A drive unit according to any one of the preceding claims, comprising a set screw acting on a bearing mount of a centre one of a plurality of rolling rings of the transmission to set a shaft clamping force of the transmission.
16. A drive unit according to claim 15, wherein a pressure point of the screw at the bearing mount is biased by a resilient washer.
17. A microscope table assembly comprising a microscope table and a drive unit according to any one of the preceding claims for adjusting the table.
18. An assembly according to claim 17, wherein the transmission of the drive unit is coupled to the table and the motor of the drive unit is operable to displace the table by way of the shaft and the transmission.