A New Constraint-based Virtual Environment For Haptic Assembly Training

This paper presents a virtual training system with the aim to make the assembly training easy and realistic through the usage of haptics and visual fidelity. In our system, we use the haptic device to help us operate the virtual training system which greatly improves the reciprocity. The training system consists of four parts:1)physics engine; 2) constraint; 3)force feedback; 4)motion simulation. The usage of physics engine helps simulate a physics world. Basic constraints are proposed to solve the shortcomings when both the physics engine and haptics are integrated in assembly tasks. The basic constraints not only simplify the assembly operation and shorten the assembly time, but also increase the visual realism when physics engine is integrated in the assembly training. To solve the problem that the physics engine can’t satisfy the haptic high update frequency, we make the physics engine and the haptic rendering run in an asynchronous execution. The force calculation consists of three parts:gravity,collision force and constraint force. The gravity is decided by the bounding box size of the parts. The collision force value is calculated based on the distance between the part and its reference part. The constraint force are divided into two types:force feedback and torque feedback. The force feedback constraint consists of slider constraint force and peg-in-hole constraint force. The motion simulation can be used to analyse the mechanism motion after all the parts have been assembled. It can also be used to test whether all the parts have been assembled correctly. Motion simulation is widely used in CAD software. With the help of the physics engine and the designed constraints, some simple motion simulations can be performed in the virtual system with haptic feedback. Moreover, except the display and physics engine modules, we enrich the training system by several widgets. The widgets are small tools that can be activated only when its function is needed. The contribution is mainly in three aspects:(1) Propose the method of setting basic constraints to solve the shortcomings when both the physics engine and haptic feedback are integrated in assembly tasks. The basic constraints make the assembly training easy and realistic through the usage of haptics and visual fidelity. (2) Assembly sequence generation based on the disassembly process. The assembly sequence is generated based on the disassembly process, and it can be optimized through assembly animation. Moreover, each part’s assembly constraint can also be identified during the disassembly process which saves the preparation time. (3) Except the display and physics engine modules, the whole training system is made up of closeable widgets. This leads to less computation and less computer memory is needed.