International Journal of Precision Engineering and Manufacturing

One of the disadvantages of biped robots is the slow movement. Jumping or running can be the solution to this. This paper describes an optimal jump trajectory generation method for biped robots. In order to conveniently create a jumping trajectory, the center of mass trajectory of the robot was divided into vertical and horizontal directions. The vertical trajectory was designed to maintain the desired flight time by considering a capacity of a actuator and the impact force at landing. The horizontal trajectory was designed to conform to the desired horizontal COM velocity at takeoff while maintaining the desired zero moment point by using preview control. We also considered the friction force between the robot and the ground and the region of motion of the robot. This process was defined as a nonlinear optimization problem, and the optimal jump trajectory was obtained. The trajectory was verified by simulation and standing jump experiment of an actual humanoid robot.

In keeping with the development of machine tools with higher speed, more axes, and a greater degree of sophistication, thermal deformation is becoming an important factor in the precision of machine tools. It has been found that thermal error accounts for about 70% of the total error in machine tools. As such, oil coolers which absorb heat from heat generating parts with cold oil are being used to reduce the error caused by thermal deformation. The gas bypass type oil coolers used in ultra-precision (temperature accuracy within ±0.1°C) machine tools are simple in structure and precise in terms of their temperature control performance; however, they have a limitation as regards temperature control due to the instability of their performance under light load conditions. In this study, an oil cooler system equipped with dual electronic valves was developed to solve the problems of the single electronic valve system and achieve more precise temperature control. To verify the performance of the developed system, its performance under the operating conditions of rated load, DIN 8602 standard, and ISO/DIS 230-3 operational mode was compared and analyzed. The proposed oil cooler system is applicable to semiconductor equipment, ultra-precision injection molds, and ultra-precision machine tools, and improves the quality of the products.

Shape reconstruction from point clouds has received considerable attention in recent years on account of its ability to directly integrate reverse engineering with rapid prototyping. The primary objective of this study is to develop an integrated system that enables one to generate input data for rapid prototyping by constructing complete shape models from point clouds obtained with various measuring devices, including laser scanners, digitizers, and coordinate-measuring machines. We first present a novel approach to reconstructing a shape from point clouds based on implicit surface interpolation combined with domain decomposition. We then propose various related algorithms for generating input data for rapid prototyping, ranging from shape manipulation to complete solid generation. The validity of this new technique is demonstrated for a variety of point clouds with differing degrees of complexity.

Direct observation of the chip-tool interface was made using transparent sapphire tools in combination with a CCD-based high-speed imagining system. The observations made for various nonferrous workpiece materials suggest that the contact conditions at the chip-tool interface be classified into three types depending on the nature of the zone of stagnant material — negligible zone of stagnant material (Type 1), zone of stagnant material that is stable and confined to the vicinity of the cutting edge (Type 2), and zone of stagnant material that expands upward from the cutting edge as cutting progresses (Type 3). Velocity profiles obtained using the particle image velocimetry (PIV) show that retardation of the chip underside occurs in the intimate contact region for the Type 2 materials while it is negligible for the Type 1 materials. Nanoindentation hardness profiles measured with depth into the chip from the chip underside indicate that the expansion of the zone of stagnant material observed for the Type 3 materials could be related to the work-hardenability of the chip material in the secondary deformation zone.

The objective of the study was to investigate the effect of 3-D stabilization exercise using a whole body tilt device. A musculoskeletal (MS) model of the whole body was developed, and used to calculate the forces in the spine, assisted by EMG measurement. The inverse dynamics was solved using the MS model of the whole body with the input data of the eight different directions of the tilt: anterior (A), posterior (P), anterior right (AR), posterior right (PR), anterior left (AL), posterior left (PL), right (R), and left (L), replicating the tilting directions of the whole body device. The anterior and posterior directions of tilt mainly induced superficial back and front muscle activations, respectively. However, deep muscles, such as the semispinalis and mulifidi, were activated in all directions of tilt. The joint resultant forces in the right and left direction of tilt were the least; but some higher activations and more diverse recruitments of muscles were demanded. In the present investigation, 3-D stabilization exercise can provide considerable muscle activation and exercise effect, with the minimum perturbation of structure. Therefore, the proposed direction of tilt can be used to strengthen the targeted muscles, depending on the patient’s muscle conditions.

This paper proposes an algorithm to estimate external force exerted on the end-effector of a robot manipulator using information from joint torque sensors (JTS). The algorithm is the combination of Time Delay Estimation (TDE) and input estimation technique where the external force is considered as an unknown input to the robot manipulator. Based on TDE’s idea, the estimator which does not require an accurate dynamics model of the robot manipulator is developed. The simultaneous input and state estimation (SISE) is used to reject not only nonlinear uncertainties of the robot dynamics but also the noise of measurements. The performance of the proposed estimation algorithm is evaluated through simulation and experiment of a four degree-of-freedom manipulator and it demonstrates the stability and feasibility in estimating the external force. The estimation results show that this approach allows inexpensive sensors as joint torque sensors to be used instead of expensive ones as force/torque sensors in robot applications.