CH628830A5 - Device for driving and positioning a machine tool bed provided with a plurality of work stations - Google Patents

Description

The invention relates to a device for driving and positioning a machine tool table provided with a plurality of equidistant work stations, arranged radially with respect to a central axis.

The use of rotary transfer machines with n stations to perform various operations on workpieces or to be checked requires a stop of the plate to perform the machining operation and a rotation of

360 °

n to bring each piece to work.

Different means are used to ensure the step-by-step rotation of the plate.

For example, a reciprocating linear actuator acts on a ratchet corresponding to each working position.

In this case, in addition to the somewhat brutal passage from one position to another, the positioning of each workstation lacks rigor.

There is also known training by a Maltese cross which has the advantage of softness and the disadvantage, when n increases, of increasing the disparity between the stopping time and the traveling time.

Indeed, the downtime of the platform being determined by the work to be performed on each station, the time to move from one station to another depends on the number of these. As the number of positions increases, the changeover time becomes more and more important compared to the downtime.

The object of the invention is to set up a device making it possible to vary the ratio between the downtime and the movement time of the plate and to ensure the precision of the positioning under the tool of each of the n workstations. set work.

To this end, the device according to the invention is characterized in that it is constituted by a Maltese cross driven by a motor rotating alternately at different speeds making it possible to determine the ratio chosen between the necessary stopping time of each work station and the time of its movement, and by the fact that means are provided to ensure an invariable and rigorously repetitive positioning of each work station during the downtime under the tool.

The means can be constituted by an adjustable stop for each work station, a pawl, rotating with the plate, engaging on the stop, and a jack exerting on the plate a pressure contrary to its direction of rotation, in order to press the pawl on the stopper at each stop.

The main advantages of such a device lie in its simplicity:

- training by a Maltese cross makes it possible to divide the circumference of the plate by a relatively large number n without unnecessary complications;

in its reliability:

- the precise positioning of each stop of the plate avoids defective machining or control.

The advantages will emerge from the description of an embodiment of the invention, given by way of example, and from the drawing in which:

fig. 1 is a schematic view of a tray equipped with a drive device;

fig. 2 is a detail of FIG. 1;

fig. 3 is a schematic view of a positioning device.

The transfer machine shown in fig. 1 essentially comprises a plate P driven in rotation by means of a Maltese cross A, the movement of which is controlled by a camshaft B, itself driven by a reduction gear R.

Each finger 1 of the cross A set in motion by the motors 2 and 3 ensures the displacement of the work stations 4 by penetrating into a notch 5 of the plate P during its angular displacement represented by FIG. 2.

If, for example, the rotary transfer machine has six stations, the plate P, on which the cross A is fixed, will have to rotate by the angle â = 60 ° to move from one station to another. This rotation will be carried out by finger 1 which will have rotated by the angle B = 120 °.

The stopping period of the plate P (machining period) corresponding to the angle c = 240 °. So, for a six-station machine driven by a Maltese cross, the downtime is twice the changeover time:

vs

T ~ =

For a machine with twelve stations, the angles will be:

360 °

â = 30 °, B = 180 ° - 30 ° = 150 °, c = 360 ° - 150 ° = 210 °

12

stop c 210 °

the ratio will be - = - 1.40

change B 150 °

For a machine with twenty-four stations, the angles will be:

360

â = = 15 °, B = 180 ° - 15 ° = 165 °, c = 360 ° - 165 ° = 195 °

24

stop 195 °

the ratio = = 1.18.

change 165 °

The angle c corresponding to a determined machining time, the angle B (change time) increases radially with the number n of stations.

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628830

In order to correct this defect in the drive through a Maltese cross while retaining the qualities of the latter as regards the flexibility of operation, the drive of the camshaft B which determines the working cycle of the machine is produced using two motors 2,3, having different rotational speeds.

These motors drive each other and are controlled by an inverter to work alternately:

The motor 2, for example, ensures a rotation of the plate equal to the angle B,

- the motor 3, a rotation equal to the angle c.

By correlatively varying the speed of the motors and the diameter of the pulleys, it is possible to obtain a determined machining time and a suitable change time.

In another embodiment, a single motor running at two speeds is used.

In another embodiment, a single motor is used controlled by a variable speed drive which can be mechanical, hydraulic or electronic.

The positioning of each station 4 under the tool must be extremely precise, failing which a shift on a single station causes errors in series. A locking of the plate at each station 4 is essential to avoid any accidental displacement during the work of the tool.

The shaft 6 supporting the plate P ensures the centering of each station 4.

The angular positioning of each station 4 is ensured by:

- a pawl 8 carried by the plate P and rotating with it,

An adjustable stop 11 fixed to the frame at the periphery of the plate P for each station 4,

- A single-acting cylinder 10 snapping into a peripheral cell 13 of the plate P.

The pawl 8 pivots on a pin 7; it is returned to position by a spring 9, and held in place against each stop 11 by a support 12.

The finger 1 of the Maltese cross A penetrates into the cell 5 of the plate P to effect the angular displacement of a station 4, that is to say

360 °

the pawl 8 passes to the next stop 11 and exceeds the station by a few tenths of a millimeter.

The jack 10 acting in a cell 13 exerts a pressure 15 contrary to the direction of rotation of the plate P and forces the pawl 8 against the stop 11, throughout the machining time at station 4.

Each stop 11 has an adjustment screw which, cooperating with a means for controlling the angular position of each station 4, makes it possible to strictly ensure the coordinates thereof in a strictly repetitive manner.

In order to carry out permanent control of the angular positioning, the periphery of the plate P includes markers 14, indexes or bores, which cooperate with an optical or magnetic, or electronic laser sighting device, detecting the error. This control device, in a simple embodiment, stops the machine; in a more elaborate embodiment, it is slaved to a device for comparison with a reference value and instantaneous correction of the error without stopping the machine, for example by acting on the adjustment of the stops 11.

R

2 sheets of drawings

Claims (8)

628830 1. A device for driving and positioning a machine tool tray provided with a plurality of equidis-tant work stations, arranged radially with respect to a central axis, characterized in that it is constituted by a Maltese cross driven by an engine rotating alternately at different speeds to determine the ratio chosen between the necessary downtime of each workstation and the time of its movement, and by the fact that means are provided to ensure a invariable and rigorously repetitive positioning of each workstation under the tool. 2. Device according to claim 1, characterized in that the Maltese cross is driven by two coupled motors rotating alternately at different speeds. 2 3. Device according to claim 1, characterized in that the means consist of an adjustable stop for each work station, a ratchet rotating with the plate engaging on the stop and a cylinder exerting on the plate a pressure opposite to its direction of rotation in order to press the pawl on the stopper at each stop. 4. Device according to claim 3, characterized in that the plate comprises peripheral marks corresponding to each work station and that means for controlling the angular position of these marks are arranged on the machine tool. 5. Device according to claim 4, characterized in that the control means are optical. 6. Device according to claim 4, characterized in that the control means are magnetic. 7. Device according to claim 4, characterized in that the control means are electronic. 8. Device according to claim 4, characterized in that the control means are slaved to a comparator and to means for instantaneous correction of deviations.