Table of Contents

Introduction	2

Research	2

Flexible Resistor	2

Fibre Optics	2

Pressurised Air	2

Capacitors	2

Method Selection	3

Progress	3

The Glove	3

The Capacitors	3

The Test	4

Problems Encountered	5

Future Planning	6

Direction	6

Finger Bend Sensors	6

Contact Sensors	6

Hand Location and Rotation	7

Revised Project Plan	7

References	8

Introduction

Sign language is not an integral part in communication learning of most Australian citizens. This forms a language barrier for those who must use sign language to convey messages to others; an especially difficult case are deaf persons talking to blind. With advances in technology comes the ability to help overcome these problems.

The development of a sensor glove with the specific goal of detecting finger motion and contact has been directed towards an effective yet compact design. The full range of motion of a hand is not required – only the minimum sensor level for current and future trends of Australian Sign Language need be considered.

Research

Traditional virtual reality gloves do not take into account the multiple joints of each finger. It is for this reason that a standard virtual reality glove was almost immediately abandoned; at least two joints in each finger are used to create different signs.

Flexible Resistor

A standard virtual reality glove does, never the less, contain components to detect finger bending. This problem is perhaps the most important to be solved in sensor glove design, at least research wise, as detecting when a finger is pressed against another is simply a button. The most common method used for detecting finger bending is the use of a flexible resistor that changes its resistance when flexed. Available from Spectra Symbol (ref 1) this is a patented commercial product, and can be bought for approx. $10 each. However these sensors are too long to cover just one knuckle, so while one could be used to cover the base knuckle, another would have to cover two. This alone is not a problem, but it does introduce extra complexity into the circuit, and various other problems may exist such as the third knuckle affecting amount of bend as well.

Fibre Optics

Another approach could be to use a fibre optic cable. When bent, not as much light will reflect through the wire and a light sensitive resistor could be used as part of an analogue to digital converter to measure this. This has more problems than the previous method – fibre optic cables are not designed to be constantly flexed and will break before long. This is not a durable design as so was again abandoned.

Pressurised Air

Air pressurised hoses with pressure sensors at the end is another approach. Major problems existing with this is that a tube must be kept pressurised, and the tubes (in addition to other equipment such as pressure sensors) are also somewhat bulky.

Capacitors

Capacitor plates are the next choice – they can be made flat to avoid the bulky state, and are easily constructed. At first a design using a compressible dielectric was tested, however this was soon abandoned as the amount of compression would be uneven when the capacitor was placed across a knuckle. Another option when using capacitors is derived from how many radios use fine tuning – by modifying the surface area. Using a sliding plate configuration, as the finger is bent it can drag forward one plate (with the other in a fixed position) thereby changing the effective capacitor surface area. This of course changes capacitance.

One useful characteristic of capacitors is that they will discharge a stored charge. The rate of this discharge is dependent upon the RC value of a circuit. For a constant resistance, the voltage level after the capacitor begins to discharge will change as the plates slide – this is the basis of detecting the amount of bend of a finger.

Method Selection

While the flexible resistor is at first the best choice to use, there are some shortcomings. The price is an obvious drawback, as for two hands a total of at least twenty are required. There is also the case of fingers crossing over. This may introduce additional forces that change the resistance – and unwanted electrical characteristic if crossing of the fingers is read as one or both fingers bending substantially.

Sliding capacitor plates provide a more rigid structure to work with, although the method is more mechanical in nature than some others.

Progress

Using an m16c/62 microchip development board as the basis for taking readings off the sensors, the first step was in method verification. The most difficult part in any project such as this is to ensure that the basic idea if fundamentally sound. If the microchip can not give proper readings, then making the glove is a moot point.

The Glove

Initial setup problems for the development board were encountered but overcome with the correct software and development files. Previous problems with the project had included what materials to create the glove out of. The glove must meet certain parameters to be both durable and effective:

Fit the hand comfortably, but not hang loose.

Easily removed without breaking any wires.

Not restrict movement.

For the purposes of testing the finger bend sensors a soccer goal keeper's glove was chosen. These gloves are specifically designed to fit the hand for better ball grip, so they won't move about, and also don't restrict movement. The drawback is that they are designed to stay on the hand and hence are not easily removed without affecting anything attached to the fingers. As this is only a bend sensor testing phase, this does not currently matter, but it will for a finalised presentation glove.

The Capacitors

Capacitor plates were constructed from cut copper rectangles 15mm x 20mm in size. Copper was chosen for its excellent electrical conductivity and ease of soldering connections to (thanks John).It is also very rigid and so won't deform as the hand moves.

To affect a high enough time constant for the circuit a 1MΩ resistor was placed in series with the capacitor. Though a 10MΩ resistor was also tried, it was deemed that the smaller time constant of the first resistor was preferred. The sensor should be able to be probed as fast as possible – the longer the time constant, then the longer the wait after discharge start until the voltage level is probed (otherwise the voltage levels will be too similar to infer amount of bend from). There is also the point that the capacitor takes time to charge, and a longer waiting time here again could produce further complications when working with a real time system for finger bend sensing.

- - - - Capacitor plates half overlapping

____ Capacitor plates fully overlapping.

While not immediately obvious from this diagram, the difference in voltage is still enough that it can be detected, especially if a few microseconds are waited before taking any readings.

Figure 1 – changing capacitance with a 0-5V input square wave signal.

The voltage probe is attached to an A-D converter input pin, with +5V from pin zero of port0. The ground pin is one of two such pins on the development board.

Figure 2 – A diagram of the capacitor plate circuit and A-D converter input.

The Test

After much reading and browsing of documentation involving the m16c/62 microprocessor, a capacitor was housed in a plastic encasing allowing the top capacitor to slide and using a sheet of plastic as the dielectric. The approximate dielectric constant of the plastic is two.

Supplying a 5V output from the development board to the circuit allows a charge to build up across the capacitor plates. When this supplied voltage is then set to 0, the plates begin to discharge. Waiting a few microseconds before taking a reading allows a large enough difference in voltages for different circuit time constants for comparison purposes.

Analogue to digital conversion within the microprocessor is done via a reference voltage, in this case 5V, and according to the following equations:

10-bit resolution (Vref X n / 210 ) – (Vref X 0.5 / 1010 ) (n = 1 to 1023), 0 (n = 0)

8-bit resolution (Vref X n / 28 ) – (Vref X 0.5 / 210 ) (n = 1 to 255), 0 (n = 0)

Where Vref is the reference voltage. 8-bit resolution does not require as long to determine, and was the first method used. This proved usable, but due to the close values of n being received, 10-bit resolution is more suitable; any magnetic fields could cause a small extra current and so a buffer zone of n values for different amounts of bend is desired.

The n values produced by the test range from 319 (plates fully overlapping) to 200 (plates only just overlapping). Repeated experiments have shown this number can vary quite substantially for a single plate overlap position; the reason for this being that the testing circuit does not hold the capacitor plates as rigid as it could. Any slight angle of the plate in any plane of rotation can affect the overall capacitance through slight variations in the distance between plates and effective surface area. This is solved through the creation of better housing, and is a prime example of the reasons for having an n-value buffer zone for discrete bend value representations.

For displaying these values to screen, the standard serial interface available through any POSIX compliant operating system is used. As windows is not completely POSIX compliant, the cygwin environment was used (www.cygwin.com). Error checking has not yet been implemented, but is planned.

Problems Encountered

Various problems have been faced in development thus far. They have been mainly restricted to simply getting the right software and debugging code, however some rather interesting conundrums have been faced with the capacitor plates and voltage level readings.

In outputting n-values to the screen, on one occasion they appeared to be almost completely random. Negative values were received (which, according to the specifications, is not possible) and their magnitude varied greatly. At first this was assumed to simply be a problem in reconstructing the data after sending it through the serial cable, or packet errors. However both these ideas were discarded after various software tests pinpointed the error to the analogue to digital converter. Magnetic interference from nearby speakers had not previously caused any problems, not had anything else. What's more, 5V indications were being given when the input pin was connected directly to ground. Everything mysteriously started to work again – it was not until the next day that it was discovered that nearby residents had experienced power fluctuations from the mains power supply. This had obviously been affecting the input power to the development board and so producing erroneous results for the tested voltage. This was an unavoidable problem, but would not affect a mobile system that relies on battery power. For testing purposes, it's simply a waste to use batteries and so this can be expected to arise again.

As stated above, different n-values have been obtained for the same overlap of the capacitor plates. This was due to small variations in how flat the plates were. For testing equipment to see if the idea would work this is not much of a problem, but does play a major factor in a real system. To solve this for later testing the obvious solution is better housing for the plates to slide within. A better setup than is currently used is to create a piston type capacitor – an inner tube able to slide within a relative stationary one. A dielectric is still required to separate the two of course, but this would provide a smaller capacitor to attach to a glove and so restrict movement less. This type of capacitor will not be created in the near future as the resources are not available – that is a manufacturing problem, not a research problem, but never the less is mentioned due to that it would improve the basic design greatly.

Instead cardboard or plastic will be used for the project to make a tight fitting housing. Cardboard is readily available from cereal boxes, is easily shaped and does not conduct electricity. It is also relatively stiff, providing a good base to attach the capacitor plates to.

Future Planning

Direction

Finger Bend Sensors

The first proof of concept has been conducted. A basic plate has been made and shown that it will work to detect the amount of finger bend. Several problems have been encountered, but none that would stop the progress of designing a glove. Only one capacitor has been made so far, and so the next logical step to take in the design process is to make more and properly attach them to a glove.

There are many expected problems to arise from this – timing will be a key issue as any induced current from voltage changes will need time to rectify. Another issue is that there are not enough input pins on the microchip board that support voltage sampling (eight to be exact) and so a multiplexed system will need to be created. This can cause subtle concerns over voltage losses and input delays, not mention any signal bouncing that may occur over the length of the wires running from the capacitor plates to the input pins.

It is expected that the current capacitor design will interfere with movement of the fingers a little; their design for a manufactured glove has been discussed above. The improved design would reduce the width of the capacitor but increase the height slightly in theory – however in practice the height won't be much more due to the soldering, wires and housing required for the current design making the bulk of its height.

Contact Sensors

There is also the matter of buttons to be placed around the glove in order to detect fine details such as touching fingers together and finger splaying. At current there are two different methods of approach, each of which will be tested: standard buttons, and simple metal contacts as used in previous research (ref: the other thesis). More research into Australian Sign Language is required in order to determine exactly where these need to be placed on each hand.

Finger contact sensors will prove to be the most difficult as putting on and removing the glove will lead to rapid breaking of soldered connections. Some sort of hardened plastic that is strapped on with valcro would provide an easily attached and removed glove, with the rigid plastic providing a good base to attach electrical components to and providing an overall robust system.

Hand Location and Rotation

While the focus of the glove is upon finger motion and contact, there is also the concern of hand roll, tilt, pitch and position relative to the rest of the body. Mike Malak is currently working on this design using infra-red LED's, however as they must be mounted on the glove then there is some overlap. Power consumption and timing are other factors that also need to be considered. If the rest of the project proves of great ease to construct and test, then this aspect will also be covered, however it is of secondary priority to finger motion and contact.

Revised Project Plan

As with many projects, the project plan is revised to provide a more realistic view of what will be accomplished; the first plan is simply what is wanted and taken from an inexperienced point of view.

This project, while falling behind the original plan, is still on track for research and development of the core idea – a sensor glove. Given that the current progress of the project can be summed up to proof of concept and microchip integration testing, it can be expected that the rest can be achieved with relatively greater speed. The following table and graph show the revised schedule.

Weeks	Tasks
6th June - 15th June	Other unit study – no project work.
16th June - 23rd June	Additional capacitor housing construction.
24th June - 7th July	Multiplexing research of sensor input.
8th July - 18th July	Additional bend sensor testing and problem fixing.
19th July - 26th July	No project work planned.
27th July - 9th August	Button research and design.
10th August - 23rd August	Contact sensor construction and testing.
24th August - 5th November	Unsolved problem fixing and general improvement.
27th July - 5th November	Thesis.

Study and work commitments have forced several weeks to be declared as no-project work weeks. Also the thesis covers the entire of second semester in conjunction with research and development. This is intentional; the project does not have to be complete in order to start the thesis. A proper project log book has been kept and can easily provide sections of early design ideas and problems encountered.

The general improvement section includes features such as proper packet error checking from and to the development board and prototype wear and tear repairs.

Co-ordination with tying the glove in to Michael's side of the project has not been included in the project plan, however it is not expected to take long and will be carried out as part of the ongoing development of the system in general.

References

Flex Sensors, retrieved 5th June 2004, http://www.spectrasymbol.com/bend.html

Cygwin Information and Installation, retrieved 5th June 2004, http://www.cygwin.com

U. S. Inan & A. S. Inan 1999, Engineering Electromagnetics, Addison Wesley Longman Inc., California.

electronic circuits

C. Newman, Translating Australian Sign Language into Speech, Thesis 2003.

A.Toney, A Novel Method for Joint Motion Sensing on a Wearable Computer, retrieved 5th June 2004, http://gro.hhhh.org/~joeboy/publications/toney_iswc1998_poster.pdf

W. Kadous, Recognition of Australian Sign Language Using Instrumented Gloves, retrieved 5th June 2004,

http://www.cse.unsw.edu.au/~waleed/thesis/node1.html

J. W. Nilsson & S. A. Riedel, 2001, Electric Circuits, International Edition, Prentice-Hall, New Jersey.

In addition to the above, numerous websites have been searched through that ever popular search engine google – http://www.google.com.au

2004-05-31T05:10:24