GB2046394A - Stylus drive mechanism - Google Patents

Abstract

A stylus drive mechanism for use in chart recorders. The mechanism is moulded in one piece from polypropylene and, in a first embodiment, comprises a first arm member 20, connected by a hinge 24 to one end of a second arm member 22 to which is also attached a stylus arm 40. The other end of the second arm member is attached by a hinge 30 to a pair of bridging members 26, 28 which are pivotally connected to the flexible arms of a fixed yoke 36. The tip of the stylus arm is therefore constrained to move linearly in response to partial rotary motion of the first arm member 20. In a second embodiment (Figure 4 not shown) only one bridging member is employed, formed by two perpendicular arms, one connected to the second arm member and the other, by a further hinge, to a flexible member which is fixed at its end remote from the further hinge. <IMAGE>

Description

SPECIFICATION Stylus drive mechanism This invention relates to a stylus drive mechanism for use in chart recorders.

It is common in chart recorders for the magnitude of the parameter which it is desired to record to be converted into electrical energy. This is then coverted into a limited rotary motion of a shaft, for example by means of a stepper motor. As the magnitude of the parameter varies, so the shaft exhibits this limited rotary motion, for instance it oscillates to and fro relative to a "zero" or "null" position just as the magnitude of the parameter itself varies towards and away from a selected zero or null value for the parameter. Various stylus drive mechanism are known for converting this limited rotary motion into a linear movement of a stylus arm, whereby a stylus mounted on the arm can mark a chart linearly in proportion to the parameter magnitude variation.

Conventional stylus drive mechanisms comprise separate members which typically cooperate through pivots and siides to provide this conversion from rotary to linear motion. However such mechanism are prone to wear due to friction and their cost includes the cost of assembling the various component parts.

We have now devised an improved stylus drive mechanism which, being integrally-formed, avoids the cost of assembling separate components and which also avoids wear arising from friction.

According to the invention there is provided a stylus drive mechanism for converting a limited rotary motion into a linear movement of a stylus arm connected, in use, to the mechanism, which mechanism comprises a plastics article comprising a first arm member for attachment to a shaft providing said limited rotary motion, a second arm member connected, at one end, by a first integral hinge to the first arm member, and, at its other end, extending to a position from which it is connected by a second integral hinge to at least one bridging member, the or each bridging member being joined by a further integral hinge to a fixable member, and the second arm member being attached, in use, to said stylus arm.

In a particularly preferred embodiment, the second arm member is connected by the second integral hinge to each of two bridging members, each bridging member being joined to a different one of two arms of a yoke (constituting the fixable member) by third and fourth integral hinges respectively.

In a further preferred embodiment, the stylus drive mechanism has one bridging member in the form of two arms fixed at right angles to one another. The second arm member is connected by the second integral hinge to the first of said two arms, said first arm lying in the same plane as the second arm member. The second of the two arms (at 900 to the first arm) > is joined by a further third integral hinge to the fixable member. The latter is in the form of a flexible arm which is fixed, in use, at its end remote from the third integral hinge.

The mechanism is preferably formed in one piece of polypropylene, e,g, by moulding, with the hinges strengthened by having the polypropylene oriented therein. Oriented polyproylene hinges are themselves known, and it is customary to form the orientation by briefly working the hinge after moulding.

In use, a stylus arm is connected to and extends parallel to the second arm member. The stylus arm duplicates the motion of the second arm member and a stylus on the stylus arm can be employed to record a linear movement of the stylus arm in proportion to limited arcuate motion supplied to the first arm member. The yoke member is fixed in position but the yoke arms flex to accommodate the motion of the second arm member at its second integral hinge end. The stylus arm may be a separate member connectable to the second arm member of the mechanism or it may be integrally-formed with the mechanism itself.

The invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows a conventional stylus drive mechanism; Figure 2 shows a stylus drive mechanism in accordance with the present invention; Figure 3 shows a plan view of the stylus drive mechanism of Figure 2, and Figure 4 shows an alternative embodiment of the stylus drive mechanism of the present invention.

The direction of movement of the components of the stylus drive mechanism shown in the Figures is indicated by arrows.

Referring to Figure 1, the stylus drive mechanism comprises a rotatable drive shaft 2 which is connected in use to a drive means (not shown). The drive shaft 2 is rigidly attached to a first arm member 4 which extends transverse to the axis of drive shaft 2. The first arm member 4 is connected to a second arm member 6 by a pivot 8. The second arm member 6 is provided at one of its ends with a stub axle 10 which slides within a fixed slide 13. The second arm member 6 has attached thereto one end of a stylus arm 14. The latter is provided at its other end with a point stylus 16.

In operation, the drive means effects a limited arcuate motion in the drive shaft 2. The arcuate motion is transmitted to the first arm member 4. This latter motion, by way of the pivots, causes the second arm member 6to pivot the stub axle 10 and to cause the stub axle 10 to slide in the fixed slide 12.

In this known manner, the resultant motion of the first arm member 4 causes the stylus arm 14, at its point stylus 16 end, to describe what can be approximated, for recording means, as a straight line. Provided the motion of drive shaft 2 is limited to a small arc, it is in substantially direct proportion to the linear motion provided to the stylus 16.

Referring to Figures 2 and 3, there is shown a rotatable drive shaft 18 which, in use, is connected to a drive means (not shown). The drive shaft 18 is connected rigidly to a first arm member 20, which is pivotally attached to one end of a second arm member 22 by means of a first integral hinge 24. The other end of the second arm member 22 is attached to each of the one ends of two equal length bridging members 26 and 28 by a second integral hinge 30.

The ends of the bridging members 26 and 28 distant from the second hinge 30 are attached by third and fourth integral hinges 32,34 one to each arm of a yoke 36. A hole 38 is provided in the yoke for enabling the neck of the yoke to be held in a fixed position, for example by means of a screw or pin.

The arms of the yoke 36 are capable of limited flexibility. The second arm member 22 is attached to a stylus arm 40, which is provided at its end remote from the second arm member with a point stylus 42.

As with conventional pen drive mechanism, in operation the drive means subjects the drive shaft 18 to a limited rotary motion. Since the shaft 18 is fixed to the first member 20 a similar rotary motion is transmitted thereto. This motion is transmitted via the hinge 24 to the second member 22, which is able to pivot about the hinge 30. This hinge 30 is also able to move over a limited distance towards and away from the neck of the yoke 36, due to the flexibility of the arms of the yoke 36. Thus, the motion transmitted to the second member 22 by the first member 20 is subjected to the limits of movement imposed upon it by the hinge 30 and bridging members 26 and 28. The resultant motion so applied to the second arm member 22 is to provide a motion equivalent to that of the second arm member 6 in the conventional mechanism shown in Figure 1.The point stylus 42 thus describes a linear movement in proportion to the limited arcuate motion of shaft 18.

Referring to Figure 4, a rotatable shaft 44 is connected in use to a drive means (not shown) and is rigidly connected to a first arm member 46 which is pivotally attached by an integral hinge 48 to one end of a second arm member 50. The other end of the second arm member 50 is pivotally attached by a second integral hinge 52 to a first arm 54 of a bridging member 56. A second arm 58 of the bridging member 56 is pivotally attached by a further, third integral hinge 60 to an elongated arm 62 of a fixable member 64. A hole 66 is provided in the fixable member 64 enabling the fixable member 64 to be held in a fixed position e.g. by a pin or stud.

The arm 62 of the fixable member 64 is capable of limited flexibility. In use, the second arm member 50 has attached thereto a stylus arm (not shown) provided at its ends remote from the second arm member 50 with a point stylus (not shown).

As described in the previous embodiment, in operation, the limited rotary motion of the drive shaft 44 is transmitted to the second arm member 50, which can pivot about the hinge 52. This hinge 52 can also move over a limited distance in a direction parallel to the longitudinal axis of the arm 54, due to the movement of the second arm 58 of the bridging member 56 about hinge 60 and flexing of the flexible arm 62.

Thus, the motion transmitted to the second arm member 50 by the first member 46 is subjected to limits imposed upon it by the hinge 52 and the bridging members 56. The resultant motion of the second arm member 50 causes the pen stylus (not shown) to describe a linear movement as described for the embodiment of Figures 2 and 3.

Claims (7)

1. A stylus drive mechanism for converting a limited rotary motion into a linear movement of a stylus arm connected, in use, to the mechanism, which mechanism comprises a plastics article comprising a first arm member for attachment to a shaft providing said limited rotary motion, a second arm member connected, at one end, by a first integral hinge to the first arm member and, at its other end, extending to a position from which it is connected by a second integral hinge to at least one bridging member, the or each bridging member being joined by a further integral hinge to a fixable member, and the second arm member being attached, in use, to said stylus arm.

2. A stylus drive mechanism according to claim 1, wherein the second arm member is connected by the second integral hinge to each of two bridging members, each bridging member being joined to a different one of two arms of a yoke, constituting the fixable member, by third and fourth integral hinges respectively.

3. A stylus drive mechanism according to claim 1 wherein only one bridging member is provided and which comprises two arms disposed at right angles to one another, the second arm member being connected by the second integral hinge to one of said two arms, said second arm member and said first arm lying in the same plane, and the second of said two arms being joined by a third integral hinge to the fixable member, which fixable member comprises a flexible arm fixed, in use, at its end remote from the third integral hinge.

4. Astylus drive mechanism according to claim 1,2 or 3, wherein the plastics article is formed in one piece.

5. A stylus drive mechanism according to any of claims 1 to 4 wherein the plastics article is moulded.

6. A stylus drive mechanism according to any of claims 1 to 5 wherein the plastics article is of polypropylene and the hinges include oriented polypropylene.

7. A stylus drive mechanism substantially as hereinbefore described with reference to either Figures 2 and 3 or 4 of the accompanying drawings.