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 six MPLs being used for neurorehabilitation research across the United States, with four more in development.
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
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.
|Absolute Position Sensor||21|
|Joint Temperature Sensor||17|
|3-Axis Force Sensor||3|
|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|
*through range of motion
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.
Revolutionizing Prosthetics 2009 Modular Prosthetic Limb–Body Interface: Overview of the Prosthetic Socket Development (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 240–249, 2011)
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).
An Overview of the Developmental Process for the Modular Prosthetic Limb (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 207–216, 2011)
The Cosmesis: A Social and Functional Interface (Johns Hopkins APL Technical Digest, Volume 30, Issue 3, pp. 250–255, 2011)