P. Schalk Els

Three dimensional musculoskeletal modelling of the abdominal crunch resistance training exercise

Abstract The aim of this study was to evaluate the benefits and limitations of using three dimensional (3D) musculoskeletal modelling (LifeModelerTM) in assessing the safety and efficacy of exercising on an abdominal crunch resistance training machine. Three anthropometric cases were studied, representing a 5th percentile female, and 50th percentile and 95th percentile male. Results indicated that the LifeModelerTM default model was capable of solving the forward dynamics simulations without adjustments. The modelling was able to indicate high risk for back injury when performing the abdominal crunch exercise as a result of the unacceptable intervertebral joint loading that occurs during the exercise. Individuals with small anthropometric dimensions such as some females and children cannot be accommodated suitably on the abdominal crunch machine which negatively impacts exercise posture and technique. Hip flexor muscle contribution in the execution of the exercise for the 5th percentile female was substantial thus reducing the efficacy of the exercise in isolating the abdominal muscles.

Vehicle Motion Measurements Using Front Facing Camera and Digital Image Correlation

Modern active vehicle safety systems rely on certain vehicle motion states to function. ABS requires the vehicle longitudinal speed to calculate the tire slip. The vehicle speed is typically estimated using the speed of all the wheels and is therefore dependent on the slip states of all the wheels. Electronic stability programs can also make more informed decisions if the vehicle side-slip angle is known. Currently the side-slip angle is not measured on commercial vehicles due to the cost of the sensors. The side-slip angle can however be estimated using multiple onboard vehicle measurements. However, these estimation techniques require accurate sensors and large excitations to estimate accurately. The measurement of the vehicle motion is therefore crucial for modern vehicle safety systems. This paper proposes a method whereby all 6 vehicle velocities can be measured using inexpensive forward facing mono and stereo cameras utilizing Digital Image Correlation (DIC) algorithms.

The Applicability of Hybrid Control to a Small Off-Road Vehicle Without a Differential

The use of controllable semi-active damping is considered by the vehicle dynamics community to be a cost effective and fail-safe method to reduce the ride comfort and handling tradeoff of a vehicle. This paper investigates the semi-active control of a suspension system for a 4-wheeled single seated off-road vehicle for both ride comfort and handling. The test vehicle is distinct with several characteristics that are not commonly observed on normal vehicles or addressed in existing literature. For instance, the absence of a differential in the driveline causes drivability and handling issues that are aggravated by increased damping. The suspension system contains controllable dampers and passive hydro-pneumatic spring-damper units. Passive damping is not entirely eliminated from the suspension, but the effect of various passive damping factors on the performance of the suspension is also investigated. Skyhook and groundhook control is implemented on a nonlinear, three-dimensional, 12 degrees of freedom simulation model to determine the achievable improvement in ride comfort and handling ability of the test vehicle. Simulation results show that reduced passive damping is capable of improving both the ride comfort and maneuverability of the test vehicle.Copyright

Tire Longitudinal Slip-Ratio Measurement Using a Camera

The longitudinal slip-ratio is one of several parameters that govern the magnitude of the longitudinal force generated by a tire and probably the most important. As such, the longitudinal slip-ratio of a tire is an essential measurement required in the construction of longitudinal tire models. In laboratory experimental tests the slip-ratio can typically be controlled by controlling the rotational speeds of two motors. However, in in-situ tests, where the slip-ratio needs to be measured, the slip-ratio is estimated from three other measurements namely the wheel speed, vehicle speed and the rolling radius of the tire. While the wheel speed is fairly inexpensive and easy to measure accurately, the accurate measurement of vehicle speed requires an expensive GPS or similar system. The measurement of the rolling radius is often performed statically and assumed constant or can be measured with an expensive laser displacement sensor. Errors in the all of these measurements are compounded when determining the slip-ratio. This paper proposes a method of measuring the longitudinal slip-ratio by performing image correlation techniques on consecutive images of the tire-road interface obtained from a single inexpensive camera. Since the method makes use of one measurement system the probability of inducing errors in the slip-ratio is reduced.Copyright

Magneto-Rheological (MR) Damper Design for High-Flowrate Suspensions

This paper presents the design of a magneto-rheological (MR) damper for an off-road vehicle where large suspension travel and high flow rates, as compared to typical passenger car suspensions, are required. The MR damper is expected to enhance the capability of the suspension system by allowing variable damping due to inherent properties of the MR fluid. MR fluids exhibit a reversible behavior that can be controlled with the intensity of a magnetic field, allowing a change in the effective viscosity and thereby in the damping characteristics of the fluid. A mathematical model of the proposed damper has been developed using the Bingham plastic model so as to determine the necessary geometry for the damper designed in this study, using the fluid flow rate and current to the electromagnet as the input variables. The model is used to compute the damping force, and the analytical results show that the designed MR damper provides the required range of damping force for the specific vehicle setup that is being used for this study. A valve-mode MR fluid channel has been designed such that the required minimum damping is reached in the off-state, and the desired maximum damping is reached in the on-state. For manufacturing and size considerations, the final design incorporates a triple pass layout with the MR fluid flowing through the three passages that are arranged in an S-shape so as to minimize the cross section of the electromagnet core.Copyright