WO1999006815A1

WO1999006815A1 - Compliance measurement device

Info

Publication number: WO1999006815A1
Application number: PCT/GB1998/002209
Authority: WO
Inventors: George Edward Torrens; Nicholas Stephen Birchall; George Frederick Pickaver
Original assignee: The Secretary Of State For Defence
Priority date: 1997-07-31
Filing date: 1998-07-23
Publication date: 1999-02-11
Also published as: JP2001512235A; GB2340948A; GB9929419D0; EP1000337A1; GB9716046D0

Abstract

A compliance measurement device having a plurality of platens (2, 3) mounted for relative movement to receive and compress a material of interest therebetween. A drive means (4, 5, 12) is provided for moving one or more of the platens (3) to apply a predetermined compressional force on the inserted material as is a means for recording changes in one or more of the external dimensions of the material under the compressional force.

Description

Compliance Measurement Device

The present invention relates to a compliance measurement device and in particular to a device for measuring the compliance of a material, including composite materials and living tissue, subjected to a compressive force.

It is sometimes necessary to have measure of the compliance of compressible materials such as flower bulbs, protective packaging or even human fingers or toes in order to predict how an example of a material or material composite from a particular class will respond to applied forces. In the case of human digits, compliance or the degree of change in the external dimensions of the digit pulp is one of the more important physical parameters of the hand which may effect the level of a person's grip on an object and consideration of this parameter could be useful in the design of , for example, tool handles. Consider, for example, workers in hazardous environments, such as may be encountered in deep sea diving, the nuclear industry or in the rescue services, which by their nature require workers to wear protective equipment. This equipment may often reduce the workers' sensory perception, movement and often their muscle strength available to apply to a tool, all of which makes the benefits of good handle design obvious.

Accordingly the present invention provides a device for measuring the compliance of a material characterised in that there is provided a plurality, preferably two, of platens mounted for relative movement and adapted to receive and compress a material of interest therebetween; drive means for moving one or more of the platens to apply a predetermined compressional force on the inserted material and means for recording changes in one or more of the external dimensions of the material under the compressional force. Thus through the determination of the changes in external dimensions of a material when subjected to a known compressive force a measure of the compliance of the material can be provided.

Usefully, one or both platens may be adapted to provide a surface which is of adjustable contour. This enables the platens to be customised, for example, shaped to conform to the shape or surface texture of the material under test.

Preferably the recording means comprises a means, such as an image recorder, for recording the spread of the compressed material across the face of a platen. As the compressional force is increased then the spread of the material increases to produce an increased image which can be recorded and measured.

Simply the material may have a printing fluid, such as ink, applied to it before insertion into the device and the image recorder may then comprise a removable print surface, such as a paper sheet, disposable on to the face of one of the platens for recording a printed image of the compressed material.

Alternatively the image recorder may be an optical recorder, for example a video camera, digital imaging device or a co-operating scanner and image sensor, disposed to record the image of the material under test which is presented on the face of a platen. This has the advantage that such images can easily be stored on computer for subsequent retrieval and manipulation and be more easily compared with images of known origin for verification systems.

Most usefully the recording means may additionally comprise a means for measuring the compressional displacement of the material along an axis of movement of the one or more platens. This additional measurement enables a cross correlation with spread measurement to be made for a more accurate compliance determination.

The invention may further provide a means, such as a strain gauge, for measuring the applied force between the platens. This would permit the material to be subjected to known variations in applied force. Additionally, the force measuring means may be operably connected to the drive means through a control switch adapted to halt the movement of the one or both platens at a predetermined applied force. This may be employed to provide a form of safety cut out which may be set to prevent a damaging force being applied to the material between the platens or could be used to vary the predetermined applied force in a controlled manner.

A support may usefully be provided which will allow a material for compression, such as a digit, to be mounted in an accurate and repeatable position in relation to the platens. Such a support may be permanently or moveably mounted on the device.

Usefully the device can be manufactured so as to be easily portable and can be configured so as to be hand held. Such a design will aid in the measurement of a variety of samples.

An embodiment of the invention will now be described, by way of example only, with reference to the drawing of the accompanying figure of which:

Figure 1 is schematic, part sectional views of a digit pulp compliance measurement device according to the present invention. Figure 2 is a schematic representation of the device of Figure 1 in use.

Referring now to figure 1 , the device 1 comprises a fixed platen 2 and a movable platen 3. Drive means comprising a stepper motor 4 in operable connection with a worm drive 5 and sliding drive 12 is housed in the body 6 of the device 1. This drive means 4,5,12 is then operably connected to the movable platen 3 to drive this platen 3 linearly along an axis connecting the two platens 2,3 as the motor 4 rotates. Due to the design of drive means, the device can accurately provide forces between 1 and 40 Newtons. Typically the device will be used to provide compressional forces between 10 and 20 Newtons with human tissue. It is however possible that higher ranges i.e. up to 40 Newtons may be used in conjunction with protective (PPE) handwear and/or materials alone. A clutch assembly 7 is disposed between the motor 4 and the sliding drive 12 and is set to slip at an applied force of 40 Newtons in order to avoid damage to an inserted digit (shown by broken line representation of a finger). A strain gauge 8 is attached to the underside of the fixed platen 2 and used to measure the force applied through the platens 2, 3 and to provide an electrical output dependent on the sensed force. A removable paper sheet (not shown) may be located on the upper surface of the movable platen 3 using spring clips 9 a, b and records the spread of the digit on to which ink has been placed. One or both platens 2,3 may be detachably mounted to the device to permit platens having different surface contours to be inserted. A support 10 on which a hand or foot can grip or rest is positioned on the side of the body 6 and is used to ensure the accurate and repeatable location of the digit on the platen 3 (figure 2). The support 10 is pivotally located on the body 6 to enable it to be used in the three positions shown in figure 2a, depending on the digit to be tested (figures 2b-d) and may be detachably mounted to the body 6. Supports customised in ways depending on the object under test may thus be substituted in order to facilitate the location of the object between the platens 2,3. A rotatable knob 11 is operably connected to the worm drive 5 and provides for the manual adjustment of the separation between the platens 2,3.

5

In use an inked digit is placed between the platens 2, 3 with the inked portion in contact with a paper sheet located on the platen 3. The movable platen 3 is then driven towards the fixed plate 2 under the control of a microprocessor (not shown) , such as a suitably programmed computer, which is operably connected l o to both the output of the strain gauge 8 and to the input of the stepper motor 4.

As the platen 3 is driven the inserted digit is subjected to increased applied force until a predetermined force is sensed by the strain gauge 8 whose output then causes the microprocessor, which acts as a control switch, to halt the platen 3 and

15 maintain this force. The digit pulp is squashed and spreads across the platen 3.

After a period of time, sufficient to record an ink print on the paper (say 0.5 seconds) the platen 3 is driven in the opposite direction to remove the force and the digit carefully extracted from between the platens 2, 3. The inked paper can then be removed and measurements taken from the image of the squashed digit.

20 The computer may also be programmed, in a manner clear to a person skilled in the art, to measure and store the number of electrical output pulses required to drive the stepper motor between a predetermined minimum and a predetermined maximum sensed applied force, corresponding to, for example, the digit being lightly held and being subject to the predetermined force respectively, and to

25 convert this to a measure of distance travelled by the movable platen 3. Hence the compression of the digit along the axis of movement of the platen 3 can be determined. Although the invention is described with reference to the measurement of the compliance of digit pulp it will be appreciated by those skilled in the art that the device may be easily modified for use with other materials without departing from the claimed invention.

Claims

1. A device for measuring the compliance of a material characterised in that there is provided a plurality of platens mounted for relative movement to receive and compress a material of interest therebetween; drive means for moving one or more of the platens to apply a predetermined compressional force on the inserted material and means for recording changes in one or more of the external dimensions of the material under the compressional force.

2. A device as claimed in Claim 1 characterised in that the recording means comprises a means for recording the spread of the compressed material.

3. A device as claimed in Claim 2 characterised in that the means for recording the spread comprises an image recorder.

4. A device as claimed in Claim 3 characterised in that the image recorder comprises a removable print surface disposable onto the face of a platen for recording a printed image of the compressed material.

5. A device as claimed in Claim 3 characterised in that the image recorder comprises an image sensor adapted to record an image presented on the face of a platen and to provide a digital output external of the device.

6. A device as claimed in any one of the preceding claims characterised in that there is further provided a means for measuring the compressional displacement of the material in the direction of movement of the platens.

7. A device as claimed in any one of the preceding claims characterised in that there is further provided a means for measuring the applied force between the platens.

8. A device as claimed in Claim 7 characterised in that the force measuring means is operably connected to the drive means through a control switch adapted to halt the movement of the one or both platens at a predetermined applied force.

9. A device as claimed in any preceding claim characterised in that the number of platens is two.

10. A device as claimed in Claim 9 characterised in that one platen is movable.

11. A device as claimed in any preceding claim characterised in that one or more of the platens is adapted to provide a face having an adjustable contour surface.

12. A device as claimed in any preceding claim characterised in that there is further provided a support on which a material for compression can be mounted so as to provide an accurate and repeatable positioning of the material in relation to the platens.