GB2043822A

GB2043822A - Stepping Mechanisms

Info

Publication number: GB2043822A
Application number: GB7909442A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-03-17
Filing date: 1979-03-17
Publication date: 1980-10-08
Also published as: GB2043822B

Abstract

A stepping cam mechanism comprises a cam element (10) rotatable about a pivot through a plurality of relatively small incremental steps, the cam element being stabilised in each set position without slip, for example by having a plurality of contiguous linear faces around its periphery. <IMAGE>

Description

SPECIFICATION Stepping Mechanisms This invention relates generally to stepping mechanisms which incorporate a cam to advance one element towards another.

The invention is particularly applicable to dressing apparatus, for example such as that described in my copending UK patent application 27137/75, Serial No. 1 566547. In the aforesaid patent application there is described apparatus for and a method of reshaping the surface of a workpiece, such as the blade of a squeegee, involving the incremental movement of a guide member and of a reshaping tool relative to one another. The preferred means of effecting this incremental movement as described in the aforesaid patent application involves the use of a rectangular cam which has one dimension differing from the other by a given amount. This difference in the two dimensions of the rectangle is equal to the depth of cut.

It is an object of the present invention to provide a stepping mechanism which includes a cam and which is adapted for the incremental movement of one element relative to another.

Although the invention is particularly applicable to the type of dressing apparatus disclosed in the aforesaid patent application, it is to be understood that it is not limited to such apparatus and has wider applications.

It is an object of the present invention to provide a stepping mechanism capable of producing a feed advance movement in steps, and which makes it possible to achieve an accurate zero setting before the feed advance takes place.

Two embodiments of stepping mechanism in accordance with the present invention will now be described by way of example and with reference to the accompanying drawings, in which:~ Fig. 1 shows a multi-face cam; Fig. 2 is a partial sectional view through a cam and lock assembly suitable for use with workpiece dressing apparatus such as referred to above; and, Fig. 3 is a schematic diagram showing the cam and ratchet wheel assembly of Fig. 2 in more detail.

Referring first to Fig. 1 this shows a multi-face cam 10 which has a central hole 12 to receive a mounting spindle. Around the hole 12 is a boss 14 which has a diametrically disposed hole through it for a retaining pin (not shown). The cam has eleven linear faces and one indented region 20. The junction between one end of this indented sector 20 and the adjacent linear face forms a stop 22. The cam is shown within a circle to illustrate how rotation of the cam, in use, from one face to the next, will produce increasingly larger increments of feed advance of an element coupled to the cam. Thus, the circumscribing circle touches the cam outline at the stop 22, and each successive face of the cam, moving in a clockwise direction, is further away from the circle.This is indicated by identifying the cam faces as +7,+6,+5,... -2, -3. The cam face which is shown at the twelve-o-clock position in the drawing is the zero setting cam face, thus giving one three setting positions to one side of the zero and seven setting positions to the other side of the zero. A cam of this nature could replace the rectangular cam described in the aforesaid patent application No. 27137/75, Serial No.1566547.

Fig. 2 shows part of a stepping mechanism which comprises an adjustable cam mechanism and a locking device. This again is appropriate for use with dressing apparatus such as described in the aforesaid patent application for increasing the depth of cut. Beneath a baseboard 30 is mounted a chassis 32 with a locking spindle 34 and a cam spindle 36 extending therethrough. Anti-friction washers 38, such as of nylon or PTFE, are positioned between the baseboard 30 and locating rings on the two spindles. A further antifriction washer 40 is provided between the baseboard 30 and the chassis 32 around the locking spindle 34. The locking spindle 34 carries a locking nut 42 beneath the chassis so that rotation of the locking spindle will cause the parts to be clamped to prevent relative movement between them.

Beneath the chassis 32 the cam spindle 36 carries a click-plate disc 44 which has a cam 46 attached to it. As can be seen in Fig. 3, the clickplate disc 44 is essentially circular and the contour of the cam 46 is such that it extends out beyond the circumference of the click-plate disc around part of its periphery. The peripheral surface of the cam 46 bears against a ball race 48 secured beneath the chassis. Associated with the click-plate disc 44 is a ratchet mechanism comprising a lever arm 50 which is pivotable about a pivot 52 and carries a roller 54 at one end adapted to engage in one of a plurality of recesses 56 around the edge of the click-plate disc. A solenoid 58 controls the pivotal movement of the lever 50 which is also provided with a return bias spring 60 connected to the end adjacent to the roller 54.The click-plate disc 44 is also springloaded to return it to its zero feed position when not in use. In use, the solenoid 58 is energised when the main motor (not shown) of the machine is switched on, thus causing the roller 54 to engage with the recess 56 associated with the zero position of the cam. Subsequent rotation of a control knob attached to the upper end of the cam spindle 36, in order to effect an incremental feed advance, causes the click-plate disc 44 to rotate and the roller 54 to jump from the zero notch to one of the other peripheral notches 56, thereby causing the cam to rotate in steps and transmitting a stepped feed motion via the ball race 48.

By these means one can effect an accurate zero adjustment of the stepping mechanism before setting it for any desired feed advance. For example, one can approach the zero setting in steps of for example 0.0010 inches to obtain a closely controlled depth of cut. A further advantage of the multi-face cam shown in Fig. 1 is that this is self-holding, by virtue of the fact that the pressure exerted against the linear cam faces tends to maintain the cam in a stable state without slip. This is accomplished in the arrangement shown in Figs. 2 and 3 by the use of the ratchet mechanism when one is using a smooth cam.

Claims

1. A stepping cam mechanism comprising a cam element rotatable about a pivot, means to rotate the cam element through a plurality of relatively small incremental steps, and stabilising means effective to maintain the cam element in each set position without slip, the cam element being biassed to return to a constant zero setting position when not subjected to external restraints.

2. A stepping cam mechanism as claimed in claim 1, in which the stabilisation of the cam element is effected by the cam element having a plurality of contiguous linear faces around its periphery.

3. A stepping cam mechanism as claimed in claim 2, in which the successive linear faces, relative to a circumscribing circle, lie respectively further from the circle as one moves around the cam element.

4. A stepping cam mechanism as claimed in claim 2 or 3, in which the cam element has a peripheral stop defined by the junction between one of said faces and an indented section of the periphery.

5. A stepping cam mechanism as claimed in claim 1, in which the cam element has a curved outline around at least part of its periphery, and the stabilising means comprises a disc which is parallel to, concentric with and secured to the cam element and which is arranged to be rotatable in controlled steps, the curved outline of the cam element extending out beyond the periphery of the disc.

6. A stepping cam mechanism as claimed in claim 5, in which the disc has a plurality of peripheral recesses engaged by a ratchet mechanism which includes a detent arranged to click from one recess to the next as the disc is rotated.

7. A stepping cam mechanism as claimed in claim 2, 3 or 4, in which the zero setting position is determined by one of said linear faces which has other such faces on each side of it, thereby enabling incremental movement in opposite directions on respective opposite sides of the zero face.

8. A stepping cam mechanism substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.