Jürgen Hielscher

Knee-ankle-foot orthosis with powered knee for support in the elderly

A prototype of a powered knee orthotic device was developed to determine whether fractional external torque and power support to the knee relieves the biomechanical loads and reduces the muscular demand for a subject performing sit-to-stand movements. With this demonstrator, consisting of the subsystems actuation, kinematics, sensors, and control, all relevant sensor data can be acquired and full control is maintained over actuator parameters. A series-elastic actuator based on a direct current motor provides up to 30 Nm torque to the knee via a hinge joint with an additional sliding degree of freedom. For reasons of feasibility under everyday conditions, user intention is monitored by employing a noninvasive, nonsticking muscle activity sensor to replace electromyographic sensors, which require skin preparation. Furthermore, foot plates with force sensors have been developed and included to derive ground reaction forces. The actual knee torque needed to provide the desired support is based on an inverse dynamics model using ground reaction forces signals and leg kinematics. A control algorithm including disturbance feed forward has been implemented. A demonstration experiment with two subjects showed that 23 % of moment support in fact leads to a similar reduction in activation of the main knee extensor muscle.

Handheld surgical drill with integrated thrust force recognition

Spine surgeries are particularly high-risk procedures with the imminent danger of spinal cord and blood vessel injuries. High accuracy and safety are important aspects in the use of medical devices during invasive interventions. For exact positioning of the drill hole, drill tip pose recognition and bone layer breakthrough detection is required. This paper presents a concept design and first results of a novel navigated handheld surgical device for bone drilling with integrated thrust force sensing and active optical markers for real-time pose recognition. The developed force sensor measures the applied thrust force on the drill tip with a cylindrical deformation element, integrated between the axial bearing of the shaft and the casing. The deflection of the deformation element is acquired by bonded resistive strain gauges. First experiments show sufficient results of the thrust force resolution for breakthrough detection.

B4.3 - Investigations of the electrical contacting of new piezoresistive polymer-ceramics

Silicon oxycarbide nanocomposite with segregated carbon (C/SiOC) belongs to the group of polymer derived ceramics (PDCs). The C/SiOC shows piezoresistive properties by mechanical load. As an advantage over metal foil strain gauges and doped sensing resistors, the C/SiOC material is expected to have a high gauge-factor (k-factor) even for high temperature applications. In order to characterize the piezoresistive properties of the C/SiOC material, force-impedance characteristic must be acequired. The paper will show different layouts of the electrical contacts and different resistance measurement by using four-terminal and two-terminal sensing. The measurement results will be compared to each other and be discussed.

Sensor System for an active Orthosis supporting the Elderly

The aging society of matured economies will face large challenges in the near future: There will be more and more elderly compared to younger people. To keep elderly persons self determined, and therefore reducing the need for personal help by maintaining the elderly ability to manage debilitating situations, a actively supporting orthosis is build. The first concept and first implementation of the sensor system to determine the user’s movements and torque is presented.

Novel approach for estimating muscular activity using mechanical effects of the human thigh as an alternative to EMG

The A novel approach for estimating muscular activity of the human thigh using mechanical effects on the surface is investigated. Muscular activity is expected to provide one of the input signals for the motor control of an active orthosis to support the elderly. Up to now Electromyography (EMG) is the gold standard for measuring muscular activity. These measuring systems are prone to electromagnetic disturbances, influence of sweat on the skin-electrode-interface and aging effects of the glue. Furthermore the necessity of wired, skin contacted and glued electrodes reduces the ergonomic qualities. Thus, EMG is inappropriate for long-term usage in the every-day environment.