Modular Prosthetic Limb

Capable of effectuating almost all of the movements as a human arm and hand and with more than 100 sensors in the hand and upper arm, the Modular Prosthetic Limb (MPL) is the world’s most sophisticated upper-extremity prosthesis. There are currently ten MPLs being used for neurorehabilitation research across the United States.

The MPL features:

Anthropomorphic (lifelike) form factor and appearance
Human-like strength and dexterity
High-resolution tactile and position sensing
Neural interface for intuitive and natural closed-loop control

Sensorization

The arm and hand pictured below contain more than 100 sensors. Many candidate technologies were prototyped and evaluated by using a custom test bed and standardized processes. In addition to sensor-specific performance criteria, other design constraints included integration, reliability, and manufacturability. At the individual joints, sensors measure angle, velocity, and torque. Additional sensors at the fingertip measure force, vibration, fine point contact, and temperature/heat flux.

sensor arm

Key	Sensor	Number
	Absolute Position Sensor	21
	Contact Sensor	10
	Torque Sensor	14
	Joint Temperature Sensor	17
	3-Axis Acclerometer	3
	3-Axis Force Sensor	3
	Additional Sensors Incremental rotor position (x17) Drive voltage (x17) Upperarm drive current (x7)	41

General Specifications

Parameter	Value	Units
Degrees of Freedom	26	DOF
Motors (Degree of Control)	17	DOC
Onboard Motor Controllers	Custom Embedded
Onboard Sensor Conditioning and Digitization	Custom Embedded
Mass of Hand and Wrist	2.9	lbs
Mass of Upper Arm with Battery	7.6	lbs
Payload Capacity (Wrist Active)	15	lbs
Payload Capacity (Wrist Static and Upper Arm Active)	35	lbs
Cylindrical Grasp Force	70	lbf
Two-Jaw Pinch Force	15	lbf
Three-Jaw Chuck Pinch Force	25	lbf
Lateral Key-Pinch Force	25	lbf
Upper Arm Joint Speed	120*	degs/s
Wrist Joint Speed	120*	degs/s
Hand Open or Close Time	300	ms
Voltage	24	volts
Communications	CAN

*through range of motion

Body Attachment

Development of a comfortable yet robust body attachment to support the range of movement and load capacity of the MPL for varying amputation levels was accomplished through investigation of multiple volume accommodating and dynamic shape-changing socket methods. These included pneumatic or air-filled bladders, hydraulic or fluid-filled bladders, vacuum-attachment methods, electro-active polymers, and shape-changing material structures. Improved surface electromyographic electrodes enhance patient comfort, and static and dynamic load distribution can be accommodated with liners, counterbalances, dynamically adapting elements, and active vacuums. Additional socket design challenges were driven by the need to provide space for controllers, for the tactor or other afferent devices, and for peripheral control (Implantable Myoelectric Sensor [IMES] and Utah Slanted Electrode Array [USEA]) transduction elements.

Cosmesis

The basic requirements for the Revolutionizing Prosthetics cosmesis are that it appear natural, be durable, be able to be manufactured, have minimal weight, meet mechanical requirements (such as minimizing energy consumption due to drag of the cosmesis to extend the operating time of the battery), support sensor function, and be repairable. Acting as an initial barrier against the environment and allowing sensors to measure force, vibration, and temperature through the cosmesis are additional requirements. Two variations of the MPL cosmesis were developed: the work glove, a functional covering that is less expensive and more durable, and the standard glove, a fully realistic cosmetic cover that includes artistic detailing to resemble a natural limb and spectrally insensitive color formulations (metamerism).

Prosthetics