Type synthesis of 6-DOF mobile parallel link mechanisms based on screw theory

Mobile parallel mechanisms (MPMs), which are parallel mechanisms with moveable bases, have previously been proposed to resolve the limited workspace of conventional parallel mechanisms. However, most previous studies on the subject focused on the kinematic analysis of some specific MPMs and did not discuss a type synthesis method for MPMs. With this in mind, we propose a screw theory-based type synthesis method to find out possible 6-degrees-of-freedom (DOF) MPM structures. In our proposed method, the 6-DOF mobility is divided into 3-DOF planar motion and 3-DOF spatial motion, both of which are realized by the transmitted planar motions of the driving units. Separately, the type synthesis of the entire MPM is divided into that of the driving unit and connecting chain. To realize 3-DOF spatial motion, two methods, applying singularity configuration and adding an additional chain, are proposed as ways to restrict undesired motions for the synthesis of the connecting chain. The driving unit is synthesized via the same type-synthesis method as the connecting chain by considering the driving unit as a planar mechanism. The method used to integrate the driving unit and the connecting chain was constructed based on whether the end pair of the connecting chain should be connected with the driving unit directly or driven by it through an actuating mechanism. As a result, 284 possible types of MPM structure are suggested and four examples of MPMs with six DOFs were synthesized to verify the feasibility of the proposed method

Human-powered vehicle capable of movement in the longitudinal and lateral directions

Human-powered vehicles, especially conventional wheelchairs, are essential tools for people with lower body disability. But their movement in a lateral direction is limited or impossible, which burdens users who want to change directions, especially in a narrow space. Thus, a human-powered vehicle that can move in a lateral direction is required. To move in any direction, many motor-driven omnidirectional vehicles have been proposed, but humans cannot manually power their mechanisms. To solve this problem, we are developing a human-powered vehicle, that is, driven by hands of the rider, that can move in both the longitudinal and lateral directions. This paper proposes such a vehicle, which has a mechanism to move in the lateral direction like people can do while walking. We designed it so that riders can operate its mechanism by analyzing the space reachable by the rider’s palms where they can effectively exert power. We constructed a prototype and conducted experiments to confirm that the vehicle moves as expected with relatively low effort. In the experiments, we confirmed the validity of vehicle operation by comparing the moving time of the vehicle with and without the lateral translation function for different travel distances and passage widths. Our results showed that the proposed vehicle moves more quickly or requires shorter moving distance in comparison with a conventional wheelchair because of the lateral movement function. In addition, we found that the threshold for utility of the function is whether the passage width is larger than the vehicle diagonal length

Mobile parallel manipulator consisting of two nonholonomic carts and their path planning

Mobile manipulators are widely used to transport and manipulate objects in industrial settings. In this paper, we propose a mobile manipulator that consists of a parallel mechanism and two two-wheel-drive carts. The planar motions of the carts are transmitted to a platform through three screw pairs of the parallel mechanism, allowing the pose of the platform to be controlled by only four motors. Kinematic analysis for such a two-cart mobile manipulator gives a Jacobian matrix, reveals the effects of nonholonomic constraints, and demonstrates that the yaw angle of the platform must be limited to avoid singular and failure configurations, and that the pitch angle is quite sensitive to uncertainties. Based on these analysis results, we present a custom path planning method for the carts. This method provides a non-optimal but easily realizable path planning algorithm with low computational cost, since the complex constraint conditions of this two-cart mobile manipulator have little influence on the proposed path generation process. The path planning process consists of four steps. We describe the motions of the carts in each step and establish a path tracking control system for the carts. Some simulations are conducted to show the motions of the carts, investigate the changes in the pose of the platform, and quantitatively evaluate the sensitivity of the platform’s pitch angle. Moreover, we construct an experimental prototype and conduct experiments to verify the validity and usefulness of the proposed mechanism and path planning method

Posture Operating Method by Foot Posture Change and Characteristics of Foot Motion

The lower limbs of the human body actually can perform the multiple-degree-of-freedom motion, just like the upper limbs. This suggests the possibility for the lower limbs to be used in the operation of multiple-degree-of-freedom devices, such as a robot arm. With that point in mind, the present paper focuses on the foot motion and examines its characteristics under the situation in which the posture of the object is manipulated by the posture change of the foot. First, we investigated how well the foot of the operator moved in accordance with the intention of the operator in order to clarify the motion characteristics of the foot experimentally by measuring the foot motion with a motion capture system under the assumption that the operator manipulates an object in virtual space. The results showed that there are differences between the intended and actual foot motions, especially when the tilt angle change was accompanied by a rotation angle change, which might be because of the joints whose axes of motion are nonparallel to the foot coordinate system, such as the talocalcaneal joint or Chopart joint. Next, an operating system considering the motion characteristics of the foot was proposed, and an experiment to verify its effectiveness was conducted. When the proposed conversion formula was used to calculate the intended foot motion based on the actual foot motion, the operability improved with respect to the required time and path-following accuracy while manipulating an object to the target posture and with respect to subjective operability

Analysis of Effect of Motion Path on Leg Muscle Load and Evaluation of Device to Support Leg Motion During Robot Operation by Reducing Muscle Load

Because the human arm and leg have a similar skeletal structure, it may be possible to use the leg to operate a robot by the master-slave method. However, operation by the leg with six degrees of freedom has two problems. First, people move their ankle with a curved motion despite intending to move it linearly. Second, it is a burden for the operator to suspend their legs in the air during operation. This study dealt with these problems. For the first problem, we hypothesized that one of the reasons was that the muscle load of a curved motion was smaller than that of a linear motion, and we quantitatively compared them by musculoskeletal analysis. The muscle loads of curved motions were 20% smaller in the anteroposterior direction, 3.1% to 23.8% smaller in the lateral direction, and 10% smaller in the vertical direction than linear motions, which showed that the hypothesis was consistent. Further, comparison of the analysis results with the results of a previous study suggested that subjects unconsciously tried to reduce the muscle load and to move closer to a linear line when they moved their ankle while consciously intending to make a linear motion. For the second problem, we developed two different prototypes of a leg support device. An experiment to evaluate the effectiveness of these devices showed that subjective exercise intensity of the tasks in the experiment using the devices was 40% or more less than that without the device, which proved the effectiveness of the devices

Reducer-integrated motor using simultaneous engagement of gear pairs with small and no differences in teeth number

The motors for industrial robots and transporting robots require high-precision positioning, large torque output, and downsizing. However, conventional motors have difficulties in downsizing or supporting large torque. In this research, we propose a novel reducer-integrated motor to solve the problems of existing motors. The proposed reducer-integrated motor has a differential gear mechanism using the simultaneous engagement of two kinds of external and internal gear pairs: one with a small difference in teeth number and the other with no difference in teeth number. Inside the reducer, linear actuators are installed. Two gear pairs with no difference in teeth number are fixed on the base and the gear pair with a small difference in teeth number is set between them. When the linear actuators revolve the external gear, the two kinds of the gear pairs engage simultaneously and the internal gear of the gear pair with a small difference in teeth number outputs the rotation. It is thought that the structure of the proposed motor can realize downsizing of the entire motor system, high load-supporting capacity, and high stiffness. In this paper, the structure and movement of the proposed motor are explained. The geometrical conditions for simultaneous engagement of the two gear pairs with small and no differences in teeth number are clarified. Through the discussion on the solution satisfying the conditions and the relation with the bending strength, a design method for the reducer of this motor is proposed. An experiment conducted on a prototype verifies that the proposed motor works as expected

車輪式移動装置用の全方向移動機構と統合型モータ機構の研究

付記する学位プログラム名: デザイン学大学院連携プログラム京都大学0048新制・課程博士博士(工学)甲第21755号工博第4572号新制||工||1713(附属図書館)京都大学大学院工学研究科機械理工学専攻(主査)教授 小森 雅晴, 教授 松野 文俊, 教授 松原 厚学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Active omni wheel possessing seamless periphery and omnidirectional vehicle using it

Vehicles that are capable of achieving omnidirectional movement will work very efficiently in factories and warehouses. To meet this requirement, various omnidirectional vehicles have been proposed, but the wheel mechanism makes precise movement difficult. The active omni wheel (AOW), which can drive itself in an arbitrary direction at any time, can address this issue, but our previous design had mechanical vibration and acoustic noise due to gaps in the outer circumference of the wheel, and its complicated structure had a large number of parts. To solve these problems, this study developed a new AOW possessing a seamless periphery and simple structure. By using barrel-shaped friction-driven outer rollers arranged alternately on the left and right sides of the wheel, gaps between the outer rollers are eliminated and a smooth periphery is realized. Additionally, the power transmission paths were simplified to reduce the number of parts. This paper explains the AOW structure and then presents analyses of structural conditions and kinematics of the AOW. A two-wheel-drive omnidirectional vehicle using the AOW was built and kinematically analyzed. Finally, experiments using the developed AOW and vehicle were conducted and their effectiveness was verified

Effect of Viewpoint Change on Robot Hand Operation by Gesture-and Button-Based Methods

Teaching pendants with multiple buttons are com-monly employed to control working robots; however, such devices are not easy to operate. As an alternative, gesture-based manipulation methods using the oper-ator’s upper limb movements have been studied as a way to operate the robots intuitively. Previous studies involving these methods have generally failed to con-sider the changing viewpoint of the operator relative to the robot, which may adversely affect operability. This study proposes a novel evaluation method and applies it in a series of experiments to compare the influence of viewpoint change on the operability of the gesture-and button-based operation methods. Experimental results indicate that the operability of the gesture-based method is superior to that of the button-based method for all viewpoint angles, due mainly to shorter non-operating times. An investigation of trial-and-error operation indicates that viewpoint change makes po-sitional operation with the button-based method more difficult but has a relatively minor influence on postu-ral operation

Motion Characteristics Analysis of a Mecanum-Wheeled Omnidirectional Mobile Robot on a Slope

Mechanisms and Machine Science book series (Mechan. Machine Science, volume 148)the 16th IFToMM World Congress 2023Mecanum-wheeled omnidirectional mobile robots (MOMRs) are widely used in the field of industry. However, since the mobility of the Mecanum wheel depends on the free rollers, limitations or undesirable behaviors may occur in the motions of the MOMR, especially when external forces are applied. Therefore, this study investigates the motion characteristics of the MOMR on a slope. First, we focus on the maximum possible acceleration considering the wheel skidding and clarify its relationship with the inclination angle of the slope and the structure of the MOMR. Then, the straight-traveling stability at the acceleration limit is analyzed to evaluate the effect of the resultant motion due to wheel skidding. The results show that the characteristics vary considerably depending on the inclination angle of the slope, and that directional dependences due to the free rollers are observed in the maximum acceleration limit and the straight-traveling stability, which should be considered in the operation of MOMRs