GB2058370A - Dynamometer Cell - Google Patents

Abstract

The rate of primary precession in a gyroscopic dynamometer cell is proportional to a force applied to its inner gimbal. The inner gimbal 13 is supported by the outer gimbal 10 with a freedom of movement about an axis YY which is at right angles to but spaced from the axis XX about which the primary precession occurs. A non- coprecessing link 15 then applies the force through a swivel 17 directly to the inner gimbal along the axis of primary precession. <IMAGE>

Description

SPECIFICATION Dynamometer Cell This invention relates to a gyroscopic dynamometer cell for measuring an applied force.

Such gyroscopic dynamometer cells are known, for instance, from UK Patent Specification 498112 and from German Patent Specification 2055794, 2119546, 2235808, 2434485 and 2058144, and there is also a general description of their operation in UK Patent Specification 1468625. A typical construction comprises an outer gimbal supported from a casing for rotation about a vertical axis, an inner gimbal supported from the outer gimbal for movement about a first horizontal axis intersecting the vertical axis, a rotor supported from the inner gimbal and driven at constant speed about a second horizontal axis which is at right angles to the first horizontal axis and intersects both the first horizontal axis and the vertical axis, a lever connected at one end by a pivoted link to the outer gimbal and at the other end by a pivoted link to the inner gimbal, and a non-coprecessing force applying link connected by a swivel device to the centre of the lever. With this construction the force applied to the lever causes corresponding primary precession of the gyroscope about the vertical axis, the rate of primary precession being directly proportional to the load and being measured electronically to give a linear digital measurement of the applied force.

Secondary precession about the first horizontal axis is eliminated by variable torque device which applies a compensating torque to the outer gimbal about the vertical axis.

It has been found that this lever can introduce an appreciable source of error. Any slight inaccuracy in the machining of this lever is a direct source of error, and any slight tipping of the lever can also have a deleterious effect on the overall accuracy. A major source of potential error arises from the effect of temperature on the lever as mentioned in the publication "Waegen und Dosieren" issue 1/1976, page 8, lines 9-7 from the bottom right-hand column.

An object of this invention is to provide a gyroscopic dynamometer cell in which the inaccuracies associated with the lever are avoided.

According to the invention a gyroscopic dynamometer cell includes an outer gimbal supported from a casing for rotation about a first axis, an inner gimbal supported by the outer gimbal for movement about a second axis which is at right angles to but spaced from the first axis, a rotor supported from the inner gimbal for rotation about a third axis which intersects both the first and second axes at right angles, and a non-coprecessing force applying link for applying the force along the first axis to a coprecessing member carried by the inner gimbal. The coprecessing member carried by the inner gimbal is preferably connected to the non-coprecessing force applying link by a pivotal connection having a pivotal axis parallel to the second axis but intersecting the first axis and a swivel connection having a swivel axis coinciding with the first axis.

This pivotal connection is preferably provided by a cross-flexure device. The inner gimbal is also preferably supported from the outer gimbal by a cross-flexure device. The coprecessing member carried by the inner gimbal may be an integral part of the inner gimbal or the shaft of the rotor.

The inner gimbal may be a motor casing supporting the rotor. A variable torque device is preferably arranged to react between the casing and the outer gimbal and a control is provided for adjusting the torque applied by the variable torque device to counteract any secondary precession. The variable torque device may by positioned between the outer gimbal and the noncoprecessing force applying link.

The invention will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side elevation of one embodiment; Figure 2 is a side elevation of another embodiment; Figure 3 is a side elevation of a further embodiment, and Figure 4 is a side elevation of yet another embodiment.

In the drawings those parts of the dynamometer cell not necessary for understanding the novel features of the invention are omitted and the same reference numerals have been used in each Figure to denote equivalent components.

With reference to Figure 1, an outer gimbal 10 is supported inside a casing frame 11 by a single bearing 12 so that it can freely rotate about the axis XX. An inner gimbal 13 is supported by two aligned pairs of cross-flexures 14 for very limited tipping movement about the axis passing through the point Y (hereinafter called the axis W). It will particularly be noted that the outer gimbal 10 is deliberately off-set to one side so that the axis YY is spaced from, but at right angles to, the axis XX.

The inner gimbal 13 is formed as part of a motor casing which encloses the unseen rotor and supports it for rotation about the axis ZZ which intersects the axis XX and W at right angles. A non-coprecessing force applying link 1 5 passes through a clearance hole 16 through the casing frame 11 aligned with the axis XX and is supported by a swivel connection 1 7 carried by a member 1 8 formed integral with the inner gimbal 13. In this manner the link 15 does not take part in the precessional movement but applies the force to the inner gimbal 13 without using a lever and pivoted links as previously required and without incurring any of the potential inaccuracies associated herewith.It will be noted that the swivel connection 1 7 includes a low friction bearing and this can of course be selected so that the link 1 5 will remain vertical despite any slight secondary precessional tipping of the inner gimbal 13.

The arrangement shown in Figure 2 differs from the described with reference to Figure 1 only in so far as the member 18 has been omitted and the rotor has been provided with an elongated shaft 1 9 which passes through a low friction bearing 20 carried by a casing 21 connected to the swivel connection 1 7. A flexible suspension such as cross-flexures may be used to connect the casing 21 to the casing of the swivel connection 1 7.

With both the Figure 1 and 2 embodiments a variable torque device may be mounted on top of the casing frame 11 to apply a compensating torque to the outer gimbal shaft in the same manner as set out in our UK Patent 1468625.

Slip-rings for supplying current to the gyroscope motor may also be positioned here.

Figure 3 differs from Figure 1 only in so far as the inner gimbal 1 3 is formed separate from the motor casing and has the member 18 formed intergral with it. The member 1 8 is connected to the casing of the swivel connection 1 7 by two aligned pairs of cross-flexures 23 and the variable torque device 24 is illustrated as it is in a novel and advantageous position between the outer gimbal 10 and the link 15. The rotor of the variable torque device 24 applies torque to the outer gimbal shaft 22 which is of course rotatively coupled to the outer gimbal 10. The stator of the variable torque device 24 is of course held against rotation by any convenient connection to the casing frame 11.Slip-rings for supplying current to the gyroscope motor may be arranged within the casing frame 11 to take full advantage of the decrease in overall height gained by positioning the device 24 inside the frame 11.

Figure 4 differs from Figure 3 only in so far as the outer gimbal 10 is extended to be supported as shown in a second bearing 25 located by the hole 1 6. A bore 26 is formed through the extension of the outer gimbal to provide a clearance hole for the link 1 5. Although the variable torque motor 24 has been shown in the same position, it will of course be appreciated that it will be somewhat more difficult to secure its stator to the frame 11 although this of course can be achieved by making the shaft 22 hollow and secures the stator to a stud extending through the hollow shaft 22 aand secured by a bracket to the casing 11.

With all embodiments it is advantageous to limit the spacing between the axes XX and W to that necessary to permit unimpeded rotation of the mechanism.

By omitting the previously taught lever and pivoted links, the overall height of the dynamometer cell is reduced and this is of particular advantage where the cell must be inhibited for use in explosive environments.

Claims (13)

Claims

1. A gyroscopic dynamometer cell including an outer gimbal supported from a casing for rotation about a first axis, an inner gimbal suppported by the outer gimbal for movement about a second axis which is at right angles to but spaced from the first axis, a rotor supported from the inner gimbal for rotation about a third axis which intersects both the first and second axes at right angles, and a non-coprecessing force applying link for applying the force along the first axis to a coprecessing member carried by the inner gimbal.

2. A gyroscopic dynamometer cell, according to Claim 1, in which the coprecessing member carried by the inner gimbal 1 3 connected to the non-coprecessing force applying link by a pivotal connection having a pivotal axis parallel to the second axis but intersecting the first axis and a swivel connection having a swivel axis coinciding with the first axis.

3. A gyroscopic dynamometer cell, according to claim 2, in which the pivotal connection is provided by a cross-flexure device.

4. A gyroscopic dynamometer cell, according to any preceding claim, in which the inner gimbal is supported from the outer gimbal by a crossflexure device.

5. A gyroscopic dynamometer cell, according to any preceding claim, in which the coprecessing member carried by the inner gimbal is an integral part of the inner gimbal.

6. A gyroscopic dynamometer cell, according to any of claims 1 to 4, in which the coprecessing member carried by the inner gimbal is the shaft of the rotor.

7. A gyroscopic dynamometer cell, according to any preceding claim, in which the inner gimbal is a motor casing supporting the rotor.

8. A gyroscopic dynamometer cell, according to any preceding claim, in which a variable torque device is arranged to react between the casing and the outer gimbal and a control is provided for adjusting the torque applied by the variable torque device to counteract any secondary precession.

9. A gyroscopic dynamometer cell, according to Claim 8, in which the variable torque device is positioned between the outer gimbal and the noncoprecessing force applying link.

10. A gyroscopic dynamometer cell substantially as described herein with reference to Figure 1 of the accompanying drawings.

11. A gyroscopic dynamometer cell substantially as described herein with reference to Figure 2 of the accompanying drawings.

12. A gyroscopic dynamometer cell substantially as described herein with reference to Figure 3 of the accompanying drawings.

13. A gyroscopic dynamometer cell substantially as described herein with reference to Figure 4 of the accompanying drawings.