Modular Prosthetic Limb

The Modular Prosthetic Limb features

MPL arm

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

sensorshand

 

Key Sensor Number
aqua Absolute Position Sensor 21
aqua Contact Sensor 10
aqua Torque Sensor 14
aqua Joint Temperature Sensor 17
aqua 3-Axis Acclerometer 3
aqua 3-Axis Force Sensor 3
aqua 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

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.

Recommended Reading

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)

Cosmesis

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).

Recommended Reading

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)