Product category:
Loadcells, Force Sensors and Torque Sensors
News Release from: Steadlands | Subject: Force sensing resistors
Edited by the Engineeringtalk Editorial
Team on 22 February 2007
Resistors feel the force of prosthetics
When Touch Bionics embarked on the design of its i-Limb Hand, it was essential that the supply of components was established in order to ensure that the benefits of the prosthetic were futureproof.
When Touch Bionics, the UK-based award winning designer and supplier of electrically powered upper limb prostheses, embarked on the design of its i-Limb Hand, it was essential that the supply of components was established in order to ensure that the benefits of the prosthetic were futureproof Being a standard, off-the-shelf part, force sensing resistors (FSRs), supplied by Tyneside's Steadlands International, have become an important part of Touch Bionics' signal collection strategy
This article was originally published on Engineeringtalk on 6 Feb 2001 at 8.00am (UK)
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Although not suitable for use on all prosthetics, the FSR is ideal for use when patients do not have the ability to activate electrodes.
In this situation, an FSR can detect the change in muscular force and allow the opening and closing of the hand with high proportional levels.
The FSR will enable the user to grip tighter, or faster even around contoured, delicate surfaces such as a wine glass.
The use of force sensing resistors also enables Touch Bionics to enhance the anatomical movement of a prosthetic hand and offer users a step-change in functionality and performance, enabling patients to do more with their prosthetic hand.
It has been developed in such a way as to provide "lighter weight" functionality for patients.
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In addition, the modularity approach to developing the system components makes it viable to develop components for all patient types at a low cost.
The i-LIMB Hand is a true next generation bionic product - it has five individually powered digits which provide the end-user with completely new grip options to enhance dexterity and the activities of daily living.
The i-Limb Hand is a terminal device that actually looks and acts like a real human hand - a goal that has never been a commercial reality, until now.
Using a traditional myoelectric two-signal input sourced from analogue electrodes (sensors placed closed to the skin to collect muscle-generated signals), the i-Limb Hand's five powered motors operate using Touch Bionics' unique control system.
This approach to control is very familiar to myoelectric users and has the benefit of allowing patients to quickly start implementing proportional control (slower/faster) and power gri' pulsing to increase a firmer grip of objects.
Again using a traditional myoelectric two-signal input, Touch Bionics' enhanced control system will shortly offer patients and end-users the opportunity to run subroutines and functions specific to activities of daily living such as pointing the index finger only (to operate a PC or telephone) or bringing together only the thumb and index finger (to pick-up small/delicate objects).
Unlike a traditional three-jaw-chuck or similar terminal device, the i-Limb Hand's five individually powered digits grip around objects and then lock when sufficient grip force has been applied - just like a real hand.
The excessive tip-force grip of more traditional devices is no longer required to maintain sufficient grip on heavier or more difficult-shaped objects.
The addition of the i-Limb Hand's cosmesis provides extra grip capability.
The new production techniques developed in-house by Touch Bionics has resulted in a cosmesis that is highly realistic in terms of skin tone, skin surface and overall accuracy to a real hand.
"Our unique combination of mechanics, controls and cosmesis re-writes the rulebook on prosthetic grip force and device functionality", commented Touch Bionics' Phil Newman.
"And FSR's are becoming a key component in developing products such as our i-Limb range".
"The proportionality of the output signal from the FSR enables certain users to achieve much more control", added Newman.
"Although Steadlands enjoy working with FSR technology in all sectors of the electronics industry, everyone within the company gets an extra kick out of working on a project which involves a higher level of human interest such as the Touch Bionics i-Limb and Salisbury District Hospital's Dropped Foot Stimulator to enhance mobility for stroke sufferers".
"We wish Touch Bionics great success with i-Limb", said Steadlands' MD Peter Craik.
Force sensing resistors (FSRs) are robust, polymer thick film (PTF) devices that exhibit a decrease in resistance when increased pressure is applied to the surface of the sensor.
This force sensitivity is optimised for use in human touch control of electronic devices such as automotive electronics, medical systems and industrial PCs.
FSRs are not a load cell or strain gauge devices though they have many similar properties.
Established technology - they have been in use for more than 25 years - FSRs do not incorporate any moving parts, so their life is almost constant.
Used widely in automotive, medical, consumer electronics such as MP3 players, mobile phones and games consoles the FSR also has many industrial applications.
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