GLM
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The grip-lift manipulandum is a device designed to study the motor control of the precision grip in humans. The motor control of the precision grip relies on the coordination of the grip force (i.e. the force applied by between the thumb and index fingers on an object) and the load force (i.e. the apparent weight of the object) when manipulating an object in space. The instrumented object manipulated by the subject is called the manipulandum or grip-lift manipulandum (GLM). The experimental setup is designed to be used in altered gravity fields (0 – 2g environments), although it can be used in a conventional gravitational environment (1g) as well. The experimental setup is composed of the grip-lift manipulandum, an environmental accelerometer, a signal conditioner and peripheral devices controlled all together by the data acquisition system.
The table below is a subset of the main features and specifications of the grip-lift manipulandum system.
| Model name | GLM |
|---|---|
| material | 7075-Aluminum |
| basic mass | 262g |
| structure | Two hollow half shells and two instrumented covers |
| dimensions | 91x37.5x48 mm (height,width,depth) |
| grip distance | 37.5 mm |
| force transducers | 2 three-dimensional Mini-40 force and torque sensors (ATI Industrial Automation,Apex, NC, USA) |
| manipulandum Instrumentation | tridimensional accelerometer for rapid movements (Analog Devices, ref. ADXL330) 300°/s tridimensional rate gyroscope (Analog Devices, ref. ADXRS300) 2 bidimensional accelerometers for shocks measurements (Analog Devices, ref. ADXL278)mounted orthogonally |
| covers instrumentation | 4 micro infrared LED (CODA micro markers) |
| Additional weights The mini-weight | Single weight of approx. 600 grams machined as one single piece of steel in order to concentrate as much mass as possible close to the center of gravity of the GLM - The design allows an ergonomic grasp o the GLM even for a subject with a small hand, such as a child. |
| Additional weights The small-weights | Range of three weights of approx. 200, 400 and 600 grams - 7075-aluminum filled with high-density tungsten carbide rods - Same visual appearance for interchangeability without the knowledge of the subject - Double press screw system for a quick assembly and disassembly on the GLM |
| Additional weights The big-weight | Three-arch structure mounted around the GLM allowing a (gravitational and) inertial torque to be generated around the grip axis. The structure defines a spherical envelope with a 100mm radius - Inertial masses of either 25 or 50 grams can be placed anywhere on the arches to generate a torque around the grip axis - All parts of the small weights are machined in 7075-aluminum. |
| extra peripherals | - Programmable metronome for cyclic movements - Buffered digital lines Inputs and outputs - Buffered analog lines Inputs - Digital triggering input/output - Kinematics acquisition system such as CODA motion system (Charnwood dymamics Ltd, Leicestershire, UK) - Orientation of gaze measurement with the Chronos eye tracking system (Chronos Vision GmbH, Berlin, Germany) - Fingers humidity measurement with a resistive circuit specifically developed for this purpose (UCL, dept. of mathematical engineering, LLN, Belgium) |
| Signal conditioner | analog and digital interface between the transducers and the data acquisition system featuring: - 19'' rack enclosure - LEMO 8-pin LEMO 1B series connectors for each ATI Mini-40 force and torque sensor. - IF-OEM3 board delivered by ATI along with the transducers with their own calibration matrix - 14-pin LEMO 2B series connector for the manipulandum and its instrumentation - stereo 3.5 mm jack for the metronome output - BNC connectors for the trigger input and output - 2-pin LEMO 0B series connectors for the humidity sensors - Clock output in RS-422 compatible format from a 2-pin LEMO 0B series connector and in CMOS and TTL compatible format from a BNC connector - BNC connectors for the extra digital input/outputs compatible with both TTL and CMOS - BNC connectors for the extra analog inputs |
| data acquisition system | cDAQ_9172 chassis with analog and digital modules (National Instruments, USA) |
| software | requires windows XP. All basic functions are implemented in the dedicated software: Setup, Calibration, Acquisition, signals display, ASCII files saving |
Applications
Experiments aboard the ZERO-G airplane during scientific microgravity campaign organized by the European Space Agency.
- Microgravity experiments
- Clinical hand evaluation
- Motor control research