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The Shadow Finger Test Unit provides researchers with access to an important component of the Shadow Dextrous Hand system for test and trials. The Finger Unit reproduces as closely as possible the four degrees-of-freedom of the human finger. It has been designed to provide comparable force output and movement sensitivity to the human finger, as well as upwardscompatibility with the Shadow Dextrous Hand. All design measurements were taken directly from the corresponding body parts of the engineering team.

The Shadow Finger Test Unit is a self-contained system with all muscles and valves integrated into the hardware design. The Shadow Finger Test Unit incorporates all necessary control systems (software provided under GNU GPL) and documentation for research and teaching purposes.

Dimensions The Finger has been designed to be as similar as possible to the finger of the human male. The Finger measures 100mm from tip to the middle of the knuckle.

Speed The Finger Test Unit is capable of moving from fully extended to fully flexed within ¼ second.

Material The entire system is built with a combination of metals and plastics.

• Fingers: Acetyl, aluminium, polycarbonate fingernails and polyurethane flesh.
• Base: Acetyl, rubber, brass, cork.
• Valve manifold: Acetyl, sintered plastic.

Strength Because the system is compliant, these are approximate measures of the maximum available output torques.

• Distal: 0.25 Nm max
• Proximal: 0.5 Nm max

Actuation

The Finger is driven by 5 Air Muscles mounted behind the finger. These provide compliant movements. Following the biologically-inspired design principle, tendons couple the air muscles to the joints. Integrated electronics in the mounting structure drive the pneumatic valves for each muscle.

Three modes of actuation are used in the Finger Test Unit. An opposing pair of muscles permits full control and variable compliance of the movement for the proximal joint. A single muscle with return spring is used for the adduction/abduction (spreading). Conditionally-coupled drive is used for the Middle and Distal phalanges of the finger to produce human movement characteristics.

Busses The Finger Test Unit presents a Controller Area Network (CAN) bus interface to the outside world. All sensor data, components, configuration and controller setpoints can be accessed over this bus. A simple protocol is used for the communication. Example code for protocol interface is supplied as part of the GPL codebase only; alternate licensing is also available as an option.

Robot Configuration The protocol used allows a variety of system-specific configuration to take place. This includes:
- enable and disable a component of the robot,
- set sensor transmission rates,
- enable and disable valve PID controllers individually,
- change PID controller sensor and target, as well as P,I,D gain values,
- change the CAN addresses used by a component,
- reset components.

The off-board PC provides access to all these functions over CANBUS via shell script, device, filesystem and program code.

Position A Hall effect sensor measured with typical resolution 0.2 degrees senses the rotation of each joint. This data is sampled locally by 12-bit ADC s and transmitted ’ on the CANBUS. The sampling rate is configurable up to 180Hz.

Pressure (Option) If the Pressure Sensing option is selected, then the pressure in each muscle is sensed by a solid-state pressure sensor mounted directly on the valve manifold, and measured with 12-bit resolution across the range of 0 4 bar. This option can be fitted at a later date.

Tactile (Option) If the Tactile Sensing option is selected, then tactile sensor data is made available as per the separate Tactile Fingertip Technical Specification. This option can be fitted at a later date.

Electronics The electronics provided is a selected subset of the Dextrous Hand electronics:
- Bus: Controller Area Network (CAN) bus interface to on-board electronics.
- Sensor Node: 1 ADC provides 4 active 12-bit sensing channels.
- Valves: Valve driver node provides timed and PID control.

On-board control The valve driver board implements PID control of individual valves. This control can be flexibly configured to take setpoint and target data from a variety of sources. These controllers can be configured via the standard robot interface and appropriate programmes, scripts and graphical examples of this are provided.

Off-board control A standard x86-compatible PC (VIA Mini-ITX: others by arrangement) running Debian GNU/Linux with the RTAI real-time system and Shadow’s GPL robot code is supplied. This can be used for initial setup, evaluation and operation, as well as serving as a template for your own control system. The PC is fitted with an external CANBUS interface.

Software in the host PC provides sensor calibration and scaling, mappings from sensor names to hardware and permits easy access to all robot facilities from C code, shell scripts, or GUI.

Microcontrollers PIC18F4580 micros are used for embedded control throughout the robot system. The firmware is provided as source on the host PC. All microcontrollers are connected to the robot CANBUS.

Valve control The valve control node drives a set of valves at 0.25mS resolution, and runs up to 20 configurable real-time PID controllers (one per valve).

The PID controllers can be configured to operate from sensor data and from user-supplied values, permitting control of joint position, muscle pressure, or user-supplied parameters.

Sensor node The Sensor Node, mounted at the base of the finger, reads joint position data and provides this to the communication bus.

Other sensors can be attached to the Sensor node by request and arrangement.

Open platform
- All source code for the microcontrollers and schematics for the electronics subsystems are provided on the host PC.
- Example RTAI real-time code along with full documentation is provided, along with access to e-mail support from Shadow.
- Solid models (VRML) and kinematic data supplied for use in 3D modelling packages.
- Software layer supports easy interfacing between this and other systems, as well as quick prototyping of algorithms and tools.