GB2089929A - Feed device having a threaded spindle and threaded members axially movable by the spindle - Google Patents

Abstract

A feed device has a plurality of axially telescopically extensible arms, each of which is drivingly connected to a respective threaded nut member in turn drivable by a single rotatable threaded spindle (5). To accommodate possible variation in the spacing of adjacent nut members being driven on the spindle, a threaded portion (G1, G3) at each end of the spindle has one or more flanks (22', 23') of the thread set back from the flank or flanks (22, 23) of the basic thread by an amount which decreases towards the middle of the length of the spindle, the reduced length flanks merging into the basic length flanks. <IMAGE>

Description

SPECIFICATION Feed device having a threaded spindle and threaded members axially movable by the spindle This invention relates to a feed device containing a threaded spindle and a plurality of female parts with driving thread, in particular for telescopically adjustable supporting arms, in which the adjacent female parts or parts of the supporting arms are adapted to be coupled together at an axial distance apart and at least one of the female parts in each case engages with the spindle.

For certain purposes of application of moving connections consisting of nuts and threaded spindle, it is necessary that from time to time two nut elements which are coupled together so that they are not rotatable relative to each other should both be situated on a threaded spindle at the same time, in other words the distance between the female parts which are coupled together is slightly less than the length of the threaded section of the spindle.

This situation occurs, for example, in a known device of telescopically variable length which is formed as cantilevered supporting arm for holding tools, measuring instruments, antennae, sensors or the like (German Patent No. 2,603,488).

According to the said Patent Specification, several supporting arm elements are longitudinally displaceable in relation to each other, supported against each other adapted to be stopped in certain positions of extension in relation to each other by means of abutments and stop devices, and designed to be coupled together in a certain sequence. The supporting arm elements are coupled together in such a manner that there is always one element having its female part in engagement with the spindle thread, and before this element leaves ths spindle thread, the female part of the adjacent element has engaged with the spindle thread.Since all the elements, or the female parts thereof, are secured against relative rotation with each other, an end play connection (yielding connection) ailowing for a certain amount of relative displacement in the direction of movement is provided for the functional reliability between the element and its female part.

In practice, there may be deviations from the theoretical distance between two adjacent elements or their nuts as determined by the stopping position compared with the length of the spindle. These deviations may be due to manufacturing tolerances or to differences in thermal expansion between the spindle and the elements carrying the nuts caused by differences in the coefficients of expansion and/or by temperature gradients between the various parts of the apparatus.

It follows from this that when ever the thread of the second female element is to be threaded onto the spindle, the turns or flight lands of the two threads are not in the correct position in relation to each other for engagement and this may lead to difficulty in threading of the nut onto the spindle or to jamming. In the worst case, the turns or lands of the thread may strike against each other and completely prevent threading.

The compensating device hitherto known, which provides a resilient connection between the nut element and supporting element, is only suitable for certain cases, e.g. if the masses to be displaced are relatively small or if the device is to be used under conditions of weightlessness.

It is an object of the present invention to provide a feed device of the type indicated above which under all conditions occurring in practice (large masses to be displaced or the like) will enable the female parts to be threaded on the spindle while the second or adjacent female part is still in engagement with the spindle, regardless of any differences in thermal expansion and without any obstruction by jamming or difficulty in threading.

To solve this problem according to the invention, the thread of the spindle and/or of the nuts, starting from each end and extending over a limited section of thread, has one or other flank set back compared with the flanks of the basic thread by an amount diminishing towards the centre of the spindle, and the flanks of the said end sections merge into the flanks of the basic thread.

Such a formation of thread provides a certain clearance over a givcn length or range of engagement which ensures that when a second or subsequent nut element is to be threaded onto the spindle, the parts will always enter into engagement without jamming or difficulty of threading. When threading takes place, the load is steadily and smoothly transferred from the nut which is being removed from the spindle thread to the other nut which is at the same time being threaded onto the spindle. This end play connection is extremely easy to achieve and requires no additional parts.

An example of the invention is described below with reference to the drawings, in which Fig. 1 is a schematic longitudinal section through a supporting arm of telescopically variable length comprising several elements one inside the other in their extended position, Fig. 2 shows on an enlarged scale the formation of the thread on the driving spindle of the telscopic arm, and Fig. 2a corresponding to Fig. 2 shows another embodiment of the parts of the feed device.

Fig. 1 shows, as an example of application, the feed device 1 in combination with a supporting arm 2 of telescopically variable length. The free end of the supporting arm in this case serves to carry an instrument (not shown), for example, a measuring instrument for use in space craft. The supporting arm 2 is composed of tubular elements Ti, T2, T3 and T4 mounted one inside the other which are displaceable relatively to each other in the direction of their common longitudinal axis A but secured against relative rotation. The feed device 1 comprises a driving spindle 5 which is arranged concentrically inside the element T and rotatably mounted on a fixed bracket 6. The mounting end of the spindle 5 is connected to a driving motor 8 by way of a reduction transmission 7.

In addition to its threaded portion G, the driving spindle 5 carries near its mounted end a cylindrical magazine section 11 the function of which will be explained hereinafter. The feed device 1 also comprises the nut elements M1, M2, M3 and M4 each of which is attached to the lower end of one of the telscopic parts T by a rigid carrier plate 14.

When the supporting arm 2 is withdrawn, all the nut elements M are disengaged from the driving spindle 5 concentric to the cylindrical section 11 with the exception of the nut element M4. This nut element remains engaged with the spindle 5 when the supporting arm is withdrawn. When the supporting arm is extended to its end position, the nut element M1 remains in engagement with the spindle 5.

The known feed device 1 operates on the principle that there will always be one nut element M in engagement with the driving spindle 5, and before one of the nut elements M has been removed from the upper or lower end of the spindle 5, the thread of the next following nut element must have entered into engagement with the thread of the spindle 5.

For this purpose, the supporting elements Tare adapted to be coupled at predetermined axial distances by means of extension stops 1 5 and 1 5'. In addition, stop elements 1 8 operating under spring action are provided, and these may sngage in recesses 20 on the adjacent supporting element T. The feed device 1 combines long extension of the supporting arm 2 with extremely short driving spindle 5. When axial transport of the parts T is transferred from one nut element M ;o the other, it happens from time to time that two nut elements M are both in engagement with the driving spindle 5 at the same time or that a nut element M must be threaded onto the spindle 5 while anther nut is still on the spindle.The thread of the spindle and/or of the nut therefore has a particular form of construction, which is described below.

As shown in Fig. 2, it is the thread on the spindle which has the particular form of construction. The spindle 5, which has a square thread, comprises a thread flight land 21 with the two thread flanks 22 and 23. The pitch of the thread is indicated at h.

Starting from the two ends of the thread of the spindle 5, threaded sections G1 and G3 are formed, within which there is superimposed on the basic thread of pitch h a thread of different pitch h'. There are three possible embodiments of this arrangement. The full lines in Fig. 2 show as first embodiment the formation of the threaded sections G1 and G3 in which the pitch h' is greater than the pitch h of the basic thread, the original formation of thread being indicated by dash. dot lines.In the threaded sections G1 and G3, starting in each case from the end of the thread, the inwardly facing flanks 22 or 23 at the end of the thread are shifted backwards by the amount a' from the original flanks, and the amount a' continuously decreases, depending on the difference in pitch, until, towards the centre of the spindle, the set back flanks 22' and 23' coincide with the original flanks 22 and 23 of the basic thread. The corrections in the threaded sections G 1 and G3 are mirror images of each other.

As shown in Fig. 2a, the second embodiment is formed by setting back the outer flanks 23 or 22 of the threaded spindle to produce the threaded sections G1 and G3, using a smaller pitch h" than that of the basic thread. In this case, the amount a" by which the flanks 23' and 22' are set back from the original flanks 23 and 22 again diminishes until the set back flanks 23' and 22' coincide with th original flanks 23 and 22.

The third embodiment, not shown here, consists of setting back both flanks 22 and 23 of the thread of each section G1 and G3. Both threads with a larger pitch h' and with smaller pitch h" are now superimposed on the thread of pitch h in the manner indicated. The reference numerals are here given to the flanks in mirror image formation at both ends of the spindle 5 in relation to the threaded section G2. This form of thread may be used both for right-handed screws and for left-handed screw.

Correction of the thread may also be carried out on nut elements or on the nut elements and the spindle.

The supporting arm 2 or feed device operates as follows: To extend the supporting arrn 2, the driving spindle 5 is rotated by the motor 8 and the supporting arm element T4 is moved away from the bracket 6 by means of the nut element M4 on the spindle 5. When the extension stops 1 5, 1 5' have made contact, the supporting arm element T3 is also carried along in the direction of extension and the nut element M3 of the supporting arm element T3 is carried in the same direction and thereby threaded ontn the driving spindle 5 so that over a limited length of displacement both the nut element M4 and at the same time the adjacent nut element M3 are ip engagement with the thread of the driving spindle 5.

The thread sections G1 and G3 are formed to enable whichever is the adjacent nut element to be threaded onto the spindle without locking or jamming of the threads. Owing to the fact that a thread cut with a pitch h' or h" is superimposed on the basic thread cut with pitch h, some play for threading is provided between the thread of the driving spindle 5 and the thread of the nut elements M4 and M3 in engagement with the spindle.

When the nut element M3 has come into engagement with the thread of the spindle, the nut element M4 is unscrewed from the driving spindle 5, and further movement of the supporting arm element T4 is effected by means of the supporting arm element T3. A detachable connection is established between the adjacent supporting arm elements by means of the stop devices 17. After a suitable path of displacement, the supporting arm element T3 is coupled to the supporting arm element T2 by way of the stops 1 5, 1 5', and the nut element M2 of the supporting arm element T2 is threaded onto the spindle 5, as described above.

The process of retraction of the arm takes place in the same manner as described above but in the reverse sequence. To couple the supporting arm elements T, the releasable stop 1 7 is overcome.

The supporting arm element T1 then withdraws while its nut element M1 remains in engagement with the driving spindle 5 at the position of maximum extension of the supporting arm 2. The effect of the formation of the thread of the driving spindle is the same as described for the process of extension.

Claims (5)

1. A feed device having a threaded spindle and a plurality of female members each with a driving thread adjacent female members being arranged to be coupled together at an axial spacing with at least one of the adjacent female members being engaged with the threaded spindle, wherein the thread of the spindle and/or of each member has d portion of limited length at each end of the thread in which portions one or other flank of the thread is set back from the flanks of the basic thread by an amount which decreases towards the centre of the spindle, and the or each said flank of the portions merges into a flank or flanks of the basic thread.

2. A feed device according to claim 1 wherein the female members are drivingly connected to axially telescopically extensible arms.

3. A feed device according to claim 1 or claim 2 wherein the portions are formed by a thread of different pitch superimposed on the basic thread.

4. A feed device according to any preceding claim, wherein the setting back of the or each flank of the portions is carried out with a lower pitch on the outer flank or with a higher pitch on the inner flank than the pitch of the basic thread.

5. A feed device constructed and arranged substantially as herein described and shown in the drawings.