Altair India

HYPERWORKS FOR STUDENTS

Projects using MotionView and MotionSolve

Dynamic Stresses in a Gear Assembly





Areas covered:

Use of an FE mesh to calculate mass and inertial properties.

Creation of Hexahedral and Shell meshes.

Transfer between FE models and MDL models.

The use of contact in transient analyses.

Flexible Body Analysis - mixing the rigid-body and flexible-body approaches in a single model.

Description of the Problem: An actuator is being designed for use in a position controller. The design is at the concept stage, and various alternatives are being worked out. The design specification of the actuator assembly calls for the design of gears, given the center-to-center distance is 106 mm and the velocity ratio is 1.28. The current proposal calls for the use of steel gears, but these may later be replaced with plastic. Obviously various options exist, but the easiest is to check if involute profile spur gears can do the job. Hand-design for gears is well-established, but FEA can provide higher precision calculations, thereby allowing the designers to use a lower factor of safety. Conventional FEA's disadvantages are twofold. First, the problem setup can be fairly demanding since the loads vary with time. Second, integrating the finite element model into the assembly-design simulation is not very easy. Traditional rigid-body mechanics is limited by the assumption that the bodies are rigid, but the option to use flexible models in a Multi-Body-Dynamics (MBD) solver opens up new possibilities.

Design of a Torque Limiter





Areas covered:

Use of an FE mesh to calculate mass and inertial properties.

Creation of tetrahedral meshes.

Transfer between FE models and MDL models.

The use of contact to investigate friction.

Preloading springs to generate contact forces.

Description of the Problem: A torque limiter is similar to a friction clutch, except that it works "backwards". Where a clutch transmits motion, the job of the torque limiter is to permit free relative motion once the design torque has been exceeded. The case at hand is at the concept-design stage. The designers are trying to achieve the specified functionality within the given package space, which is tightly limited. The shaft, supported by bearings at both ends, has a nut which carries an axial load. The gear, mounted on the shaft, receives the drive. If the axial load exceeds the design value (90 dN) the gear must slip - that is, the shaft should not rotate. As long as the axial load is less than the design load, the shaft must rotate with the gear. To achieve this, the designers have chosen to rely on friction. They want to use springs to exert a frictional-force between the gear and the shaft. Using power-screw calculations, the gear-torque can be related to the axial load on the nut. If the spring-preload is set correctly, drive will be transmitted as long as the friction-load is more than the gear torque. When the gear torque exceeds the friction-forces, the gear will slip. The design requirement is to establish the required spring-load to ensure that slip occurs at the design load.

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