Bistable Solenoid Locking Element for Knee Orthosis
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Solution Overview
Problem
Existing electromagnetic locking elements for joint orthoses and prostheses consume high power due to their monostable construction, limiting the distance patients can walk before needing battery recharge.
Innovation Solution
A bistable lifting magnet with a coil and permanent magnet, combined with a spring system and energy storage devices, allows for energy-efficient operation by maintaining the locking element in a partially extended position without current, using capacitors to control the pin's position and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a monostable solenoid is used for the locking mechanism, then the joint can be locked securely in the extended position, but the power consumption is high which reduces the walking distance before battery recharging is needed
Solution Approach 1:
The patent transitions from a monostable solenoid to a bistable solenoid with two stable positions (locked and unlocked). The bistable design allows the pin to remain in either extended or retracted position without continuous power supply, as the spring system and magnetic forces maintain both positions stably. This dynamic change enables the locking mechanism to securely hold the joint in extended position while consuming minimal power during normal operation.
Solution Approach 2:
The control system activates the solenoid coil only periodically - briefly to transition between locked and unlocked states - rather than maintaining continuous power supply. The capacitor stores energy and releases it in controlled pulses to move the pin between positions. This periodic activation dramatically reduces overall power consumption while maintaining reliable locking capability when needed.
2Reliability
If a monostable solenoid with gravity-assisted locking is used, then automatic locking on power failure occurs, but the power consumption significantly reduces the walking distance
Solution Approach 1:
The bistable solenoid design inherently provides fail-safe locking behavior. When power fails, the solenoid naturally returns to its default stable position (typically the locked position due to spring pre-compression), automatically securing the joint without requiring active control. This eliminates the need for continuous power monitoring or control logic while maintaining automatic protective locking.
Solution Approach 2:
The spring system in the bistable solenoid automatically manages the locking state during power failures. The stored mechanical energy in the compressed spring provides the force needed to return the pin to the locked position when electrical power is unavailable, making the system self-regulating and eliminating the need for additional power consumption or complex control circuits.
3Use of energy by moving object
If a bistable solenoid with energy storage devices is used, then power consumption is significantly reduced for longer walking distances, but the device complexity increases
Solution Approach 1:
The patent integrates the capacitor directly into the solenoid assembly, combining the energy storage function with the actuation mechanism. The capacitor is positioned within the solenoid housing and electrically connected to the coil, creating a compact integrated unit. This merging approach reduces the need for separate power management components and simplifies the overall device architecture despite the added bistable functionality.
Solution Approach 2:
The bistable solenoid design serves multiple functions: it provides secure locking, enables fail-safe operation, reduces power consumption, and maintains compact size. The spring system simultaneously provides the restoring force for bistability and the fail-safe mechanism. The capacitor serves both as an energy storage device and a buffer for controlling the activation timing. These multi-functional elements reduce the need for additional separate components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The bistable lifting magnet design significantly reduces power consumption, enabling longer walking distances for patients by maintaining the locking element in a partially extended position without current, ensuring secure locking and extended battery life.
Implementation Method 1
a bistable solenoid with at least one coil and at least one permanent magnet
Implementation Method 2
The spring system increases the force of the solenoid and allows for energy-efficient operation
Implementation Method 3
one or more electrical energy storage devices, in particular capacitors, a control system which, with the aid of switches, discharges the energy storage device(s) via the at least one coil of the solenoid
Data Source
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AI summary
The present invention discloses an electromagnetic locking element (4) for locking the joint (3) of a joint orthosis or a joint prosthesis, in particular a knee orthosis or knee prosthesis, comprising a bistable solenoid (5) with at least one coil and at least one permanent magnet; a pin (6), which can be extended and retracted with the aid of the solenoid, for locking the joint, one or more electrical energy stores (9), in particular capacitors, and an electrical circuit (11) which, with the aid of semiconductor switches, discharges the energy store or stores via the at least one coil of the solenoid in such a way that the pin is extended.