Mechanism-parameters design and validation of transformable tracked robot based on goal programming

Abstract: It is critical to design a reasonable and suitable mechanism parameter for the robot, as it plays an important role in the robot's adaptability to the environments. To efficiently design a robot that was able to adapt itself to an environment where the obstacles were given, a mechanism-parameter designing method was hereby put forward based on the goal programming in order to obtain the optimized robot that could adapt to the environment mentioned. According to configuration evolution and configuration characteristics of tracked robot, a transformable tracked robot configuration was proposed, which only need 3 motors and its single arm could be used as the tracked robot with 2 arms. In theory, applying the ellipse theorem to the configuration design of the tracked robot could ensure that the tracks could be continuously tensioned with the track length unchanged, when the arm was swing. The continuous tension of track was realized by using cam and spring structure. On the basis of the above, the stair climbing and the gully crossing mechanism of the tracked robot was analyzed by using the swing arm's front and back swing. And then, the relationship between the structure parameters of the robot and the stair and gully obstacles was obtained, and the function of the obstacle performance was built. According to the requirements of the goal programming, we selected the distance between driving wheel and the driven wheel, maximum length of the swing arm, driving wheel radius and angle between the track and the horizontal plane in the process of obstacle surmount as the decision variables. Then the values of the highest stair and the widest gully were used to the performance function, and the objective function and object constraint of the goal programming were obtained. As the robot must meet some conditions in the obstacle surmounting process and must improve the calculation efficiency, the initial constraint and no-slip constraint in obstacle surmounting, and the upper and lower boundaries of decision variables were defined, and then the absolute constraints were obtained. Finally, the goal programming model of the structural parameters for the transformable tracked robot was established. Due to the limitation and low efficiency of the traditional algorithm for solving the goal programming model, this paper used genetic algorithm. Penalty function method was used to deal with the individuals that did not meet the absolute constraints to reduce their fitness to reduce the possibility of gene transfer to the next generation. In order to prevent the genetic algorithm converging the local optimal solution, the program ran many times, and the average value was taken from the 10 results, and then the structure parameters were as follows: the distance between driving wheel and the driven wheel was 290 mm, the maximum length of the swing arm was 326 mm, the driving wheel radius was 60 mm. To verify the feasibility of the obtained structural parameters, the track model was obtained by using the software Adams' development function to replace the flexible track with small rigid body. Then the dynamic platform of the tracked robot was built and the simulation experiments of climbing 160 mm stair and crossing 300 mm gully were carried out, which verified the adaptability of climbing the stair and crossing the gully and obtained the driving torque required in the obstacle surmounting process. In order to further verify the rationality of the structural parameters obtained from the goal programming model, a prototype was developed and tested on the stair and gully. The prototype succeeded in surmounting 160 mm high stair and 300 mm wide gully, which proved the performance of the robot and also the feasibility of the structure parameter designing method based on goal-programming. This study provides an effective method for robot structure parameter designing.