Active wrist prosthesis. Allows rotational movements in both directions. The gearbox is the strong point of this invention, with a planetary stage followed by a cycloidal one, with two opposing discs for mechanical balance.
The problem consists in the realization of an active prosthesis of the wrist in pronation-supination, composed of a commercial motor and a custom mechanical reducer that meets the high standards of compactness required, capable of guaranteeing the performance of a human wrist, silent operation and irreversibility of the system. with the engine off.
Nowadays, active wrist prostheses are underdeveloped, especially due to the difficulty of being able to create an active device compact enough to fit into the anthropometric encumbrances and into the patient’s cradle.
In addition to this, to be used by patients, the mechanism must meet high standards of strength and silence, and provide irreversibility of the system in the event that the user tries to turn the wrist with the engine off.
Current Technology Limits
- In terms of commercial availability, most devices are passive, generally 1 or 2 DOF devices, with few motorized rotators available
- Few rotary motors available
- Most multi DOF wrists are serial mechanisms which, while simple to design and manufacture, are more prone to excessive length
- Active wrists that can reach moments similar to the healthy human pulse can be quite heavy or long
- Relatively compact active wrists have very low torque. This trade-off must be addressed in the development of more sophisticated wrist prostheses
Our Technology and Solution
This prosthetic wrist has a particular gearbox, connected to an electric motor: the first stage is epicyclic, operating with three friction wheels, and the second is cycloidal. This last stage uses two opposing discs (with an angle of 180 ° between them) with the typical shape of cycloidal applications, and a camshaft, to allow their reciprocating movement against the external profile. The resulting transmission is robust and rigid, with low play and a high ratio (264: 1) to weight and dimensions.
- Double cycloidal / planetary stage
- Eccentric drive shaft
- Lobate discs
- High reduction ratio
- High strength and transmissible torque
- Structural and construction simplicity
- High compactness of the union of the epicycloidal and cycloidal mechanisms
- High degree of customization of the two-stage reduction system
- Dynamic balance
- Absence of vibrations
- High resistance to mechanical shocks