Comparison of Two Methods for In Vivo Estimation of the Glenohumeral Joint Rotation Center (GH-JRC) of the Patients with Shoulder Hemiarthroplasty

Determination of an accurate glenohumeral-joint rotation center (GH-JRC) from marker data is essential for kinematic and dynamic analysis of shoulder motions. Previous studies have focused on the evaluation of the different functional methods for the estimation of the GH-JRC for healthy subjects. The goal of this paper is to compare two widely used functional methods, namely the instantaneous helical axis (IHA) and symmetrical center of rotation (SCoRE) methods, for estimating the GH-JRC in vivo for patients with implanted shoulder hemiarthroplasty. The motion data of five patients were recorded while performing three different dynamic motions (circumduction, abduction, and forward flexion). The GH-JRC was determined using the CT-images of the subjects (geometric GH-JRC) and was also estimated using the two IHA and SCoRE methods. The rotation centers determined using the IHA and SCoRE methods were on average 1.47±0.62 cm and 2.07±0.55 cm away from geometric GH-JRC, respectively. The two methods differed significantly (two-tailed p-value from paired t-Test ∼0.02, post-hoc power ∼0.30). The SCoRE method showed a significant lower (two-tailed p-value from paired t-Test ∼0.03, post-hoc power ∼0.68) repeatability error calculated between the different trials of each motion and each subject and averaged across all measured subjects (0.62±0.10 cm for IHA vs. 0.43±0.12 cm for SCoRE). It is concluded that the SCoRE appeared to be a more repeatable method whereas the IHA method resulted in a more accurate estimation of the GH-JRC for patients with endoprostheses

An optical system to measure the end effector position for on-line control purposes

This article describes an optical system to measure the coordinates of a manipulator’s end effector, which can move in a horizontal plane of approximately 1 × 1 m2. Two rotatable laser beams track a retroreflector pair, mounted on the end effector. The coordinates are calcu-lated from the measured beam rotations. The resolution and reproducibility of the coordinate measurement is 0.05 mm. The maximum tracking speed mounts up to 5 m/s. Using components similar to those applied in CD players, the total cost of all mechanical, optical, and analog elec-tronic components can be kept as low as $3000. On an IBM AT-compatible PC, it takes 1 ms to calculate the x and y coordinates from the measured signals. 1

New concepts for control of power transients in flywheel assisted drivelines with a CVT

Vehicle powertrains with a continuously variable transmission (CVT) have a large freedom in controlling the engine speed and the torque at the wheels. Due to rotating inertias within the engine and transmission, the response of the vehicle during large engine speed shifts may appear reluctant or even counteractive. To overcome this behaviour, the CVT is augmented with a planetary gear set and compact steel fl ywheel. The new transmission seamlessly combines two contradictive features: the driveability in terms of the pedal-to-wheel response is greatly improved and a large leap towards optimal fuel economy can be made. This can be achieved by cruising the vehicle at extremely low engine speeds which is possible by the large ratio-coverage of the CVT. The latently impassive pedal-to-wheel response that normally would emerge is now eliminated by the gear set and the flywheel. In this paper two control strategies for the engine throttle valve and the CVT ratio shift speed are presented and analysed. The control laws are able to realize high driveability and fuel economy at the same time. Results from simulations will be discussed