The invention relates to a device for controlled rotational positioning of a carrier plate rotatably mounted on a support member, the device being used e.g. in a rotary feeder or a rotatable rotor frame, a drive motor being connected to a rotational drive means acting between the carrier plate and the support member, in accordance with the preamble to claim 1.

The rotatable mounting is normally achieved with the aid of roller bearings which have the advantage of low friction and, also, long life. In addition, it is usual to use a gear trans¬ mission as rotational drive means. However, such an arrangement involves certain disadvantages since an exact rotational positioning is impeded by the carrier plate and associated equipment having an angular momentum, which give raise to an uncontrollable, continued rotational movement when the drive motor is stopped, and the final rotational position will be indeterminate. Moreover, a gear transmission gives rise to positioning errors due to the necessary backlash between meshing teeth .

The object of the present invention is to provide, against this background, an improved rotational positioning device which enables exact, repeatable rotational positionings, even when the carrier plate with asscociated euqipment has a considerable mass, and consequently a large angular momentum.

This object is achieved in accordance with the invention by the carrier plate being mounted in sliding bearings on the support member and that the rotational drive means includes an endless drive belt, as disclosed in claim 1. The sliding bearings permit a certain friction between the carrier plate and the support member, although this friction is relatively low. Using simple means (see claims 7 - 9 relating to suitable material for the slide elements of the sliding bearings) it is possible to

achieve that the carrier plate can be rotationally set to an exact desired position, with a suitable common adjustment of the mentioned friction, the weight of the carrier plate and associated equipment and the rotational speed achieved by the motor and rotational drive means. The sliding friction namely enables a very short and controllable breaking distance. The endless drive belt also gives a no-play and exact movement translation between drive motor and the carrier plate.

Further suitable distinquishing features of the rotational positioning device in accordance with the invention are disclosed in the dependent claims and will be apparent from the detailed description given below of a preferred embodiment, which is made with reference to tha accompanying drawing, where

Fig. 1 schematically illustrates in a central cross-section, to a certain extent exploded, the parts included in a rota¬ tional positioning device in accordance with the inven¬ tion,

Fig. 2 is a view from above of an annular member with circular¬ ly distributed slide elements included in the rotational positioning device according to Fig. 1 ,

Fig. 3 is a view from above seen according to the arrows

III - III in Fig. 4 of the rotational positioning device with associated drive means.

Fig. 4 is a central section through the rotational positioning device according to Fig. 3.

The device illustrated on the drawing (see Fig. 4) is placed on a rigid foundation 1, e.g. a floor, on which a support member in the form of a circular support plate 2 is mounted on feet 3 screwed to the floor such that the plate 2 can be kept in a desired, suitably horizontal position with the aid of adjusting screws 4 in the feet 3.

In the support 2 there is a central, circular hole 5 (Fig. 1) and welded to the upper side of the plate there is a holding collar 6 concentric with, and somewhat spaced from the hole edge 5a, the holding collar 6, accommodating a sliding bearing means 7 for an upper, rotatable carrier plate 8. The latter is similarly circular and provided with a central hole 9, defined by an integral, downwardly projecting collar 10. The carrier plate θ is assumed to the be included in a rotatable apparatus or machine, e.g. a rotary feeder, a mechanical handling apparatus or an industrial robot, for which it is essential that exact and repeatable rotational positionings can be achieved.

For this purpose the sliding bearing means 7 includes an annular member 11, which is non rotatably attached to the holding collar 6 of the support plate 2 and provided with inernal conical surfaces 11a, lib facing upwards and downwards, respectively. A plurality of cylindrical slide elements 12a are inserted with a press fit in corresponding bored blind holes in the upper conical surface 11a (see Fig. 2) . These circularly distributed slide elements 12a engage against the collar 10 of the carrier plate 8, the lower part of which is bevelled to a supplementary conical surface 10a (Fig. 1).

According to Fig. 4, the carrier plate 8 is kept in a stable position with the aid of a radially internally arranged and vertically oriented sleeve 13, which extends through the central holes 5 and 9 of the support plate 2 and carrier plate 8, the upper part of the sleeve 13 being threaded into the collar 10 of the plate 8, while its lower part has a radially extending external flange 13a with a sloping, upwardly facing conical surface 13b. Circumferentially distributed, cylindrical slide elements 12b are inserted in bored blind holes on this conical surface 13b, similarly to the as the slide elements 12a in the conical surface 11a, so that both pairs of opposing

conical surfaces 10a, 11a and lib, 13b are kept fixed in rela¬ tion to each other by the intermediary action of both slide element arrays 12a, 12b.

The slide elements 12a and 12b suitably comprise a thermo¬ plastics material, which is relatively stiff and has low friction against the opposing conical surfaces. A suitable material is polyamide, preferably with an addition of a lubricant, such as an oil molecule composition.

The rotational drive of the carrier plate 8 relative the support plate 2 is achieved with the aid of a servo-controlled electric motor 14 which is adjustably attached to the upper side of the plate 8. The motor 14 has a right-angled drive 15 with a pinion 16, which is in mesh with an endless toothed belt 17, which is kept tensioned round the pinion 16 and an exteriorly toothed ring 18 on the holding collar 6, such as to rotate the carrier plate 8 when the motor is activated.

The described rotational positioning device can be modified in many ways within the scope of the following claims. Instead of circumferentially disposed slide elements, a closed annular slide ring can be used, e.g. placed in an annular groove. If it is found suitable, one array of slide elements can be replaced by a roller bearing. In certain cases it may be sufficient to arrange a single (upper) array of slide elements, or a single slide ring, e.g. if the carrier plate 8 has a large diameter in relation to the dimensions of the equipment it carries, and the mounting will thus be stable without axial (vertical) retention from below.

The electric motor can also be replaced by some other kind of motor, e.g. a fluid controlled drive unit.