Yoshihiro Kai

Development of a walking support robot with velocity-based mechanical safety devices

Safety is one of the most important issues in walking support robots. This paper presents a walking support robot equipped with velocity-based mechanical safety devices. The safety devices consist of only mechanical components without actuators, controllers, or batteries. The safety device is attached to each drive-shaft of the robot. If the safety device detects an unexpected angular velocity of the drive-shaft, the safety device can switch off all motors of the robot and lock the drive-shaft. The safety devices can work even if the robots controller does not work. Firstly, we describe the characteristics of the safety device. Secondly, we explain the walking support robot and the structure and mechanism of the safety device. Thirdly, we show the walking support robot which we developed. Finally, we experimentally verify the effectiveness of the safety device.

Evaluation of task-performance of a manipulator for a peg-in-hole task

The paper deals with kinematic evaluation of task-performance of a manipulator for a peg-in-hole task. First, a condition of the manipulator for avoidance of jamming on the chamfer of a hole is derived. Secondly, strict conditions for the peg-in-hole task are obtained by adding the condition to Whitneys conditions. Thirdly, a suitability measure of the manipulator for avoidance of jamming on the chamfer (MAJC) is proposed. Finally, it is shown that successful assembly should be guaranteed from not only Whitneys conditions but also the condition for avoidance of jamming on the chamfer and that task-performance of a manipulator should be evaluated on the base of not only a dexterity measure for assembly (DMA) but also the MAJC.

Kinematic evaluation of manipulator for peg-in-hole task

In a peg-in-hole task, the task-performable areas are graphically evaluated using gray scales from the manipulability and a DMA (dexterity measure for assembly) in the reachable areas of a manipulator. The DMA is represented as relation between a unit value of joint angular errors to be allowable in the task and a unit value of joint angular errors of the manipulator. The DMA consists of a DMGC (dexterity measure for geometric conditions) and a DMFC (dexterity measure for force conditions). These measures relate to task conditions including both compliance of an RCC (remote center compliance) and compliance of the manipulator joints. The task conditions are represented as the physics models. The manipulability measure is used to check the neighborhoods of the mechanical singularities of the manipulator. A graphic representation enables us to understand easily the relations between the task and the kinematics of the manipulator, since it integrates the DMA and the manipulability measure in the reachable areas.

Development of a walking support robot with velocity and torque-based mechanical safety devices

Safety is one of the most important issues in walking support robots. We have proposed a walking support robot equipped with velocity-based mechanical safety devices. The safety device is attached to each drive-shaft of the robot. If the safety device detects an unexpected high angular velocity of the drive-shaft, the safety device stops the robot. In this paper, we propose a walking support robot equipped with not only the velocity-based mechanical safety devices but also torque-based mechanical safety devices, in order to further improve human safety. A torque limiter and a switch are used in the torque-based safety device. The torque-based safety device is also attached to each drive-shaft of the robot. If the torque-based safety device detects an unexpected high torque of the drive-shaft, the torque-based safety device switches off all motors of the robot. The velocity-based safety devices and the torque-based safety devices can work even if the robots controller does not work, because these safety devices consist of only passive mechanical components without actuators, controllers, or batteries. Firstly, we describe the characteristics of the velocity-based safety device and the torque-based safety device. Secondly, we explain the walking support robot equipped with the velocity-based safety devices and the torque-based safety devices. Thirdly, we show the walking support robot which we developed. Finally, we verify the effectiveness of the velocity-based safety device and the torque-based safety device by experiments.

Development of a rehabilitation robot suit with velocity and torque-based mechanical safety devices

Safety is one of the most important issues in rehabilitation robot suits. We have proposed the structure of a rehabilitation robot suit equipped with two mechanical safety devices. The robot suit assists a patients knee joint and the safety devices consist of only passive mechanical components without actuators, controllers, or batteries. We call one device the “velocity-based safety device” and the other the “torque-based safety device”. We expect a robot suit with the safety devices to be able to guarantee the safety even when the computer fails to operate functionally. In this paper, we begin by reviewing the characteristics of the safety devices and the structure of the rehabilitation robot suit equipped with the safety devices. Then we show a prototype robot suit developed based on the proposed structure. Finally, experimental results are demonstrated to verify the effectiveness of the safety devices in the prototype robot suit.

A robot suit with hardware-based safety devices: Frequency response analysis of a velocity-based safety device

Safety is one of the most important issues in rehabilitation robot suits. We have designed a rehabilitation robot suit equipped with two mechanical safety devices called the “velocity-based safety device” and the “torque-based safety device”. The robot suit assists a patients knee joint. The safety devices work even when the robot suits computer breaks down, because they consist of only passive mechanical components without actuators, controllers, or batteries. The torque-based safety device stops the robot suit if it detects an unexpected high joint torque. Similarly, the velocity-based safety device stops the robot suit if it detects an unexpected high joint angular velocity. However, the mechanism for detecting the unexpected angular velocity in the velocity-based safety device may resonate with a walking cycle, because the mechanism has a bar, a rotary damper, and two tension springs, that is, the mechanism is a mass-spring-damper system. In this paper, we firstly review the robot suit equipped with the safety devices. Secondly, we analyze the mechanism for detecting the unexpected angular velocity and examine whether the mechanism resonates with a walking cycle. Finally, we present experimental results to verify the effectiveness of the velocity-based safety device.

A walking support robot with velocity, torque, and contact force-based mechanical safety devices

Safety is one of the most important issues in walking support robots. We have proposed a walking support robot equipped with velocity and torque-based mechanical safety devices. The velocity-based safety device and the torque-based safety device are attached to each drive-shaft of the robot. If the velocity-based safety device detects an unexpected high angular velocity of the drive-shaft, it stops the robot. If the torque-based safety device detects an unexpected high torque of the drive-shaft, it cuts off the torque transmission and switches off all of the robots motors. This paper proposes a new walking support robot equipped with not only the velocity-based and torque-based safety devices but also contact force-based safety devices. The contact force-based safety device stops the robot if it detects an unexpected large contact force between the robot and the environment (e.g. humans). These safety devices will work even when the computer breaks down, because they consist of only passive mechanical components without actuators, controllers, or batteries. Firstly, we describe the walking support robot with the safety devices. Secondly, we show the prototype walking support robot which we developed. Finally, we verify the effectiveness of the safety devices by experiments.

Evaluation of manipulators based on a kinematic accuracy index considering task-directions

Some manipulation tasks have directions of required manipulators motion, and directions for which kinematic accuracy is required in the motion. This paper proposes an index (KAIT: Kinematic Accuracy Index for Task-directions) that allows us to evaluate the kinematic accuracy of manipulators considering the task-directions. The KAIT is applicable to tasks which require consideration of not only the position of the manipulators endpoint but also the orientation of it. First, we derive the KAIT. Second, we evaluate some postures of a 2-degrees of freedom (DOF) planar manipulator on the basis of some indices that have been proposed (Salisburys condition number, Yoshikawas manipulability measure and Chius task compatibility) and the KAIT, respectively. Further, we evaluate some postures of a 3-DOF planar manipulator on the basis of the KAIT. Finally, from the evaluation results, we discuss the usefulness of the KAIT.

A velocity-based mechanical safety device for human-friendly robots: An analysis of the shaft-lock mechanism

We have proposed a velocity-based mechanical safety device for human-friendly robots in order to improve the safety of the robots. The device is attached to each of the robots drive-shafts. If the device detects an unexpected drive-shafts angular velocity, it locks the drive-shaft. The device works even when the robots computer breaks down, because it consists of only passive components without actuators, controllers, or batteries. In the device, the rotational angle of the drive-shaft after detecting the unexpected velocity and before locking is important because an increase in the angle increases the risk of collision between the robot and humans. However, we have never analyzed the angle. In order to design the safety device efficiently, we need to analyze the angle. In this paper, we analyze the rotational angle of the drive-shaft. First, we review the velocity-based mechanical safety device. Next, we analyze the rotational angle. Lastly, we verify the effectiveness of the analysis by experiments using the velocity-based mechanical safety device which we developed.

A robot suit with hardware-based safety devices: Transient response analysis of a velocity-based safety device

We have developed a rehabilitation robot suit with two hardware-based safety devices - the velocity-based safety device and the torque-based safety device. The robot suit assists a patients knee joint. The torque-based safety device stops the robot suit if it detects an unexpected high joint torque. Similarly, the velocity-based safety device stops the robot suit if it detects an unexpected high joint angular velocity. The safety devices work even when the computer breaks down, because they consist of only passive mechanical components without actuators, controllers, or batteries. However, we have never analyzed the transient response of the velocity-based safety device. In order to design the velocity-based safety device efficiently, we need to analyze the transient response. In this paper, we firstly review the robot suit equipped with the safety devices. Secondly, we analyze the transient response of the velocity-based safety device. Thirdly, we simulate the transient response of a new velocity-based safety device in order to demonstrate the usefulness of the transient response analysis. Finally, we present experimental results to verify the effectiveness of the transient response analysis.