GB2404990A

GB2404990A - A spring device for measuring pushing and pulling forces

Info

Publication number: GB2404990A
Application number: GB0417616A
Authority: GB
Inventors: Melvyn Hughes; Andrew John Dodds
Original assignee: COMMOTION Ltd
Current assignee: COMMOTION Ltd
Priority date: 2003-08-06
Filing date: 2004-08-06
Publication date: 2005-02-16
Anticipated expiration: 2024-08-06
Also published as: GB0318440D0; GB2404990B; GB0417616D0

Abstract

A device for indicating pushing and pulling forces 10. The device 10 comprising a helical spring 12 having a base end 14 and a free end 16, the free end 16 being movable relative to the base end 14 by compression or extension of the spring 12. The device 10 also comprises a tube 26, the base end 14 of the spring 12 being in contact with a cap 28 on the end of the tube 26. An elongate actuator 18 is operative on the free end 16 of the resilient means 12 and has a plunger 20 at one end and means for attaching loads 22 at the other end. The free end 16 of the spring 12 is movable relative to the base end 14 by pulling on the attaching means or pushing on the plunger of the actuator 18. The force applied is indicated by an indicator 24 which moves with the free end 16. The device is suitable for use in teaching demonstrations and experiments.

Description

A DEVICE FOR INDICATING PUSHING AND PULLING FORCES

The present invention relates to a device for indicating pushing and pulling forces.

In school teaching demonstrations and experiments, the frictional force acting on an object, for example those acting on an object being pulled across a surface, may be measured using a spring balance. The spring balance then indicates the force acting on the object. It is desirable to be able to indicate pushing forces as well as pulling. However, known spring balances cannot measure pushing forces.

The invention in its various aspects is defined in the claims, to which reference should now be made.

Advantageous features are set forth in the appendant claims.

The invention will now be described in more detail, by way of example, with reference to the drawings, in which: Figure 1 is a side view of a first embodiment of a device for indicating pushing and pulling forces embodying the present invention; and Figure 2 is a perspective view of a second embodiment of a device for indicating pushing and pulling forces embodying the present invention.

The device for indicating pushing and pulling forces of Figure 1 comprises resilient means in the form of a spring 12 having a base end 14 and a free end 16. The spring 12 is a helical spring, of wire, with spaced-apart turns in the unstressed state. The free end 16 of the spring 12 is movable towards the base end 14 by pulling or pushing the free end 16 to compress the spring 12 and this reduces the spacing between turns.

An actuator 18, in the form of a cylindrical rod, extends through the spring 12. One end of the actuator 18 projects beyond the free end 16 of the spring 12 forming a plunger 20. The other end of the actuator 18 projects beyond the base end 14 of the spring 12 forming an end 22 for attaching loads. A spring-engaging abutment ring 24 is located around and secured to the actuator 18. The abutment ring is of larger outside diameter than the spring 12 and bears on the free end 16 of the spring 12.

The abutment ring 24 tapers radially in thickness on both sides to a point to form an outer edge 25. The outer edge of the abutment ring 24 also forms an indicator or cursor.

The spring 12 is located in a body or housing comprising a tube 26 of clear or transparent plastics material. The tube 26 is closed at one end by a base cap 28 and at the other end by a stop cap 30. The base end 14 of the spring 12 is in contact with the base cap 28 which forms an abutment for the spring 12. A stop ring 32 is located around and fixed to the rod of the actuator 18 between the abutment ring 24 and the stop cap 30. The stop ring 32 tapers radially in thickness on one side to a point to form an outer edge 33. The base cap 28 has a through hole 34 with a diameter that is larger than the diameter of the rod of the actuator 13 but smaller than the diameter of the spring 12. The stop cap 30 has a through hole 36 with a diameter that is larger than the diameter of the rod of the actuator 18 but smaller than the diameter of the stop ring 32. The tube 26 is transparent and the engaging ring 24 can be seen through it.

The tube 26 has graduations 38 on it along its length which the abutment ring 24 moves relative to when loads - 3 - are applied to the actuator. The graduations 38 form a scale and the outer edge 25 of the abutment ring 24 forms an indicator or cursor. The force applied to the actuator 18 is indicated by the position of the abutment ring 24 relative to the graduations 38.

In this example, means for attaching loads to the end 22 are provided by a hole 40 through which one end 42 of an S-shape hook 44 passes.

A U-shape hanger or bail 46 of bent wire is pivotally connected to the housing. The free ends 48 of the wire hanger or bail 46 are bent inwardly and extend into holes in the stop cap 30. The bail 46 is arranged such that it extends to beyond the end of the plunger 20 even when the plunger 20 is fully extended.

A pushing force acting on an object can be measured by pushing the object with the plunger 20 while holding the housing or body of the device by the tube 26. A pulling force acting on an object can be measured by attaching the free end 50 of the S-shape hook 44 to an object and pulling on the U-shape bail 46 or on the housing. Application of either of the pulling or pushing forces, causes the abutment ring 24 to engage with the free end 16 of the spring 12. The spring 12 is then compressed between the abutment ring 24 and the base cap 28. The abutment ring 24 moves relative to the tube by a distance indicated by the position of the outer edge 25 of the abutment ring along the graduations 38 on the tube 26 which correspond to the applied force.

The stop ring 32 and the stop cap 30 cooperate to prevent the actuator 18 from completely coming out of the tube 38. - 4 -

Resilient means other than a spring 12 may be used.

For example, a rubber tube or Belville washers may be used.

In the example shown, the resilient means 12 is described acting in compression. In an alternative embodiment, the resilient means 12 can act in tension. In which case, the resilient means 12 is attached at one end to an abutment on the stop cap 30 and at the other end to the actuator 18.

The device for indicating pushing and pulling forces of Figure 2 is similar to that of Figure 1 and like components have been given the same reference numerals.

The plunger 20' is of non-circular cross-section having a flat surface 110 on one side. The cross-section in this embodiment is T-shaped with the cross-piece of the T providing the flat surface. The hole 36' in the stop cap 30 is of complementary T-shaped cross-section so that the actuator cannot rotate relative to the stop cap 30.

By providing the flat surface 110 on the plunger 20', the plunger 20' can be written on using a write on/ wipe off marker typically used for writing on white boards.

The end surface 148 of the stop cap 30 can be used as an indicator. In use, as the plunger 20' moves, marks may be made on the plunger 20' where it aligns with the indicator formed by the end surface 148 of the stop cap 30 to give an indication of the applied force. The device 100 can then be calibrated by a user. For example, a pair of scissors can be attached to the hook 50' and the amount this causes the actuator 18' to be moved can be recorded by marking the plunger 20' where it enters the stop cap 30. Another pair of scissors can be attached to the hook 50' and a mark can be made in the same way. The process can be repeated to produce a scale in "scissor units". - 5 -

Conveniently, the marks can be made by writing on the flat exposed side of the T-shape plunger 20'. These marks can then by easily erased if a user so wishes so that a new scale can be added.

A T-shape plunger 20' and a complementary through hole in the stop cap 30' provides a rigid plunger 20' while having a large flat surface which is easy to write a scale on and read a scale from. It is also easy to write a scale on and read a scale from the device 100 because the T-shape of the plunger 20' and through hole prevent it from rotating.

The base cap 28' has an internally screw threaded through hole 122 which receives a complementary externally screw threaded bush 127. The bush 127 has a through hole 36' with a circular cross-section extending through it and the actuator 18' passes through the through hole 36'. A washer 121 bears onto the end of the bush 127 and the base end 14 of the spring 12 bears onto the opposite surface of the washer 121. An annular lip 123 projects axially from the surface of the washer 121 and fits inside the end turn of the spring 12 to centre the spring 12 inside the tube 26. The periphery of the outside end of the bush 127 is profiled with knobs 118 to make the bush easy to be gripped for turning. As the bolt 127 is screwed and unscrewed, it moves the washer 121 longitudinally, and thus the spring 12 and abutment ring 24' along the tube 26, in order to change the position of the indicator formed by the edge of the abutment engaging ring 24' so that it can be aligned with the zero marking on the graduations 38. This is particularly beneficial because repeated extensions and compressions may deform the spring slightly and this zeroing arrangement can be used to compensate for any error this causes. - 6 -

The free end of the plunger 20' terminates in a tip of rubber which also has a sector shaped pad 132 at its extremity for use in pushing against objects.

The abutment ring 24' is tapered on one side only so that the side that engages the spring is flat.

The shank of the actuator 18' between the abutment ring and the end 22 has a cruciform cross-section. The transverse dimension of the cruciform adjacent the abutment ring 24' is larger than along the rest of the actuator 18' to help locate the end of the spring 12 adjacent the abutment ring 24'.

The hook 50' is generally S-shape. The portion 42' which extends through the hole 40 in the end 22 for attaching loads is straight. Beyond the hole 40 it is formed with one or more (in the drawings we have shown two) discete sharp bends 144 rather than a continuous curve as in the embodiment of Figure 1 to make the hook less easily removed from the hole 40.

The stop cap 30 is inserted into the end of the tube 26. It has a peripheral flange 120 which abuts the end of the tube and a main portion which fits inside the tube.

The ends 48 of the wire hanger or bail are inserted through aligned holes in the wall of the tube and in the sides of the end cap to retain the stop cap in position.

The bail is resilient so that the ends can be removed from the holes to enable the device to be assembled and disassembled.

The base cap 28' is attached to the tube 26 by sonic welding. The sonic welding between the base cap 28' and the tube 26 provides a particularly strong join between these components which prevents the base cap 28' being - 7 - forced out of the tube 26 when the spring 12 is n compressed.

The stop cap 30' and the end cap 28' have flats on one side so that the housing may be placed on a surface without a tendency to rotate.

In other respects the device of Figure 2 is the same as that of Figure 1.

All the components other than the spring, the hook and the rubber tip may be moulded in plastics material.

In another embodiment, the scale can be written on the actuator 18, 181 and an indicator can be marked on the tube.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention. - 8 -

Claims

1. A device for indicating pushing and pulling forces, the device comprising: a resilient means having a base end and a free end, the free end being movable relative to the base end by compression or extension of the resilient means; a body, the base end of the resilient means being in contact with an abutment on the body; and an elongate actuator operative on the free end of the resilient means, the actuator having a plunger at one end and means for attaching loads at the other end; wherein the free end of the resilient means is movable relative to the base end by pulling on the attaching means or pushing on the plunger of the actuator, the force applied being indicated by indicating means which move with the free end of the resilient means.

2. A device for indicating pushing and pulling forces according to claim 1, wherein the body is tubular and the resilient means is disposed inside the tubular body.

3. A device for indicating pushing and pulling forces according to claim 1 or 2, wherein the actuator is a rod extending through the resilient means.

4. A device for indicating pushing and pulling forces according to any preceding claim, wherein the body is clear and marked with a scale and the actuator carries the indicator which is visible through the body.

5. A device according to any of the preceding claims in which the body is transparent so that the actuator can be seen through the body.

6. A device according to claim 5 in which the indicating means comprise a scale and a cursor, the cursor and scale - 9 - moving relative to one another when a force is applied to the actuator.

7. A device according to claim 6 in which the cursor is mounted on the actuator and the scale is marked on the body, the cursor being visible through the body.

8. A device according to claim 6 in which the cursor is marked on the body and the scale is on the actuator, the scale being visible through the body.

9. A device according to any of the preceding claims in which an abutment is provided on the actuator which engages the free end of the resilient means, the abutment carrying the indicating means.

10. A device according to claim 9 in which the abutment on the actuator comprises an abutment ring which is disposed around and fixed to the actuator, the outer edge of the abutment ring comprising the indicating means.

11. A device according to any of the preceding claims in which the plunger has a flat writing surface on one side.

12. A device according to any preceding claim in which the plunger has a non-circular cross section and passes through a complementary shaped hole in an end cap of the body so that the plunger cannot rotate relative to the I body.

13. A device according to any preceding claim, wherein the plunger has a T-shape cross-section and passes through a complementary T-shape through hole in one end of the body.

14. A device according to any of the preceding claims in which the abutment on the body is adjustable axially - 10 relative to the body whereby the position of the free end of the resilient means in the unstressed state relative to the body can be moved.

15. A device according to claim 14 in which the body includes a screw threaded bush which fits in a screw threaded hole at the base end of the body, turning the bush relative to the hole in the body causing the position of the abutment to be adjusted.

16. A device according to claim 15 in which the abutment is formed by a washer placed between the inner end of the bush and the base end of the spring.

17. A device according to claim 15 or 16 in which the screw threaded hole is provided in an end cap of the body which is attached to the rest of the body by sonic welding.

18. A device according to any of the preceding claims in which the body comprises a cylindrical tube.

19. A device according to any of the preceding claims in which the resilient means comprises a helical spring and the actuator extends along the axis of the spring through the centre of the spring.

20. A device according to any preceding claim, wherein I the resilient means acts under compression.

21. A device for indicating pushing and pulling forces according to any preceding claim, wherein the resilient means is a spring.

22. A device for indicating pushing and pulling forces according to any preceding claim, wherein the free end of the plunger is made from resilient material.

23. A device according to any preceding claim, wherein a bail is attached to the body, the bail extending to beyond the free end of the plunger when the plunger is fully extended.

24. A device for indicating pushing and pulling forces substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.