THE FORCE ACCEPTANCE UNIT
This is the big unit which the patient will move a part of. It forms the interface between the subject and the system. |
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It consists of two parts |
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The lever arm (usually metallic and often with numbers on it normally rotates freely unless you lock it). |
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The Head Assembly
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This houses the motor (active dynamometer) and is responsible for controlling the lever arm. |
Active Dynamometer
This is within the head assembly and controls the machines speed by altering the force. Normally this is achieved by electronic servomotors or a hydraulic valve which controls the lever arm in both directions. The motor resists a pushing force (concentric) and pulls in the opposite direction to the pushing force to give eccentric.
Measurements of angular velocity, position and force/torque are taken by the active dynamometer. If the force sensor is at the center of rotation (like in the Cybex norm, Biodex multijoint system 3 and the Isocom) then the machine measures torque. If the force sensor is positioned on the lever arm then it measures force (as in the Kin-Com AP) and this is converted to torque.
In some systems the moment which the motor can generate has been deliberately limited in the eccentric phase (which limits the maximal angular velocity). More recent designs offer high angular velocities but relatively low active moments. Until recently with the advances in technology new machines like the Iocom can now offer both high speeds and high active moments.
The Seat
The seat is used to stabilise the subject.
The Control Unit
This is where the computer will make all its mistakes (remember the user is never wrong!). Be aware that the computer will take every available opportunity to lose the important data you have just collected, embarrassing you in front of the subject simply because it didn’t realise (very stupidly for a computer) that you had pressed the wrong button and then confirmed you didn’t want to save the data.
Specific Attachments
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These are used to attach the subject to the machine. |
The load cell (this is where the
various different attachments fix into. It is able to slide up and down
in relation to the lever arm). In some systems the force exerted on the
load cell is converted to an electrical signal (usually in both directions)
and this measures force (so don't drop it).
