Masatoshi Hikizu

Practical obstacle avoidance using potential field for a nonholonmic mobile robot with rectangular body

A real-time obstacle avoidance algorithm based on sensor data is required for mobile robots. When a mobile robot is nonholonomic and it has polygonal body, the method using configuration space is usually applied. But, it is complex and it needs much computing power. On the other hand, artificial potential field is often used for real-time obstacle avoidance, however, most of them consider a mobile robot as an ominidirectional movable point. Therefore, we propose a new method of practical obstacle avoidance for a mobile robot with rectangular body. Action points of repulsive forces from obstacles are located in both the front and rear of robotpsilas body. Their forces are generated according to the distances between obstacles and robotpsilas body. Rear forces are transferred to the front by inverting and the resultant force moves the robot. This method is very simple and effective.

Inchworm robot grippers for clothes manipulation

Manipulating deformable objects like clothes, plastic, and paper by a robot is very challenging. This paper focuses on clothes manipulation as an example. A tracing manipulation method is used here to find a corner of the clothes. In this paper, tracing refers to tracing the clothes’ edge, with the robot’s movement based on feedback from sensors. One difficulty during this edge tracing is to make the robot trace smoothly and speedily without dropping the clothes in the process. This is due to the fact that deformable objects are sensitive to contact forces. A solution to this problem is to design a special robot gripper that can trace the clothes without having to worry about the clothes slipping away. In this paper, the development of inchworm-type grippers is proposed. Two sets of grippers inside a robot hand will allow the robot to trace the clothes more freely because there will always be a gripper firmly holding the clothes at any time. A unique tracing method for towel spreading using the inchworm grippers is also discussed. Experimental results have demonstrated the effectiveness of both the proposed grippers and also the algorithm.

Inchworm robot grippers in clothes manipulation — optimizing the tracing algorithm

Unlike factory robots that handle rigid objects most of the time, home service robots need to be able to handle soft objects like clothes, rubber, paper etc. Dexterous manipulation is important when dealing with these deformable objects. For example, in clothes manipulation, it is important for the robot to recognize the shape of the clothes to identify it before sorting or folding it. In order to do that, the robot must first reveal the original state of the clothes which can be done by spreading it. Procedure for clothes spreading for any clothes will always involve grasping of two correct corners before the item is spread. Finding a corner of the clothes can be done by using image processing. The second corner is relatively harder to find because it has to be a corner next to the first corner and not appose it. Edge tracing method ensures the corner found to be a corner next to the first corner. One difficulty during edge tracing of clothes by a robot is to make it trace smoothly and fast without dropping the clothes in the process. The problem is how to retrieve or regrasp the clothes when it is in danger of slipping away from the gripper. This task is difficult due to the fact that deformable objects are sensitive to contact forces. One solution to this problem is to design a gripper that can trace without having to fear for the clothes to slip away. The usage of inchworm type grippers is proposed. Two sets of grippers will allow the robot to trace the clothes more freely because either one gripper will always be holding the clothes. This paper discusses the optimization of the parameters for edge tracing using the inchworm type grippers for towel spreading through experiment.

Clothes Manipulation by Robot Grippers with Roller Fingertips

Unfolding or spreading is a very important process in clothes handling in order to sort out whether an item is a shirt, skirt, pants, etc. Spreading of clothes basically involves holding two corners of the clothes next to each other. The problem is finding the two corners. Usage of tracing manipulation to find the second corner can solve this problem. However, there are also problems concerning tracing manipulation. One of the major problems is how to retrieve the fabric when it is in danger of slipping away from the gripper. The robot may be able to detect that the fabric is about to slip, but it is hard to retrieve or prevent it. If the robot tries to regrasp the fabric, it would probably slip away. If the robot tries to retrieve the fabric without regrasping it, it would most probably drag the fabric along instead of retrieving it. This is due to the fact that deformable objects are sensitive to contact forces. A simple solution to this problem is to design a special gripper that can trace the edge smoothly and can also perform fabric retrieval. This paper proposes a unique tracing method for towel spreading using two sensors-equipped grippers with a rolling mechanism at the fingertips. Tracing in the context of this paper involves tracing the towels edge, with the robot movement based on feedback from sensors. The gripper will allow more flexibility towards fabric manipulation. Experimental results have demonstrated the effectiveness of both the method and the grippers.

The Effects of Negative Driving Torque in Servomotor Drivers

In many applications, a servomotor driver controls a motor to drive its load with either positive or negative driving torques. The negative driving torque is defined as torque applied to load in the reverse direction of the motor rotation. When the servomotor driver controls the motor to drive its load with negative driving torque, the effects of the negative driving torque may damage the servomotor driver. Thus, in this paper, we study the effects of negative driving torque in commercial servomotor drivers by using the numerical simulation that combines the simulation of the control system with that of the electronic circuit. The simulation results show that the negative driving torque is used for decelerating the motor and compensating the disturbance torque. When the negative driving torque is required, the servomotor driver generates regenerative current that flows from the motor back into the power supply and makes the power supply voltage rise

SPREADING OF CLOTHES BY ROBOT ARMS USING TRACING METHOD

ABSTRACT This paper proposes a method of clothes spreading using two robot arms with sensors equipped grippers and a fixed CCD camera. This research is focused on getting the robot arms to find and hold two side-by-side corners of a rectangular towel, one by using a simple image processing method and the other by using a unique tracing method. The tracing method in our context is a method of tracing the towels edge by a robot arm based on the feedbacks from sensors and also images from the CCD camera. By using this method, we have succeeded in spreading a rectangular shaped towel.

Real-Time Obstacle Avoidance Using Potential Field for a Nonholonomic Vehicle

Obstacle avoidance is an important function for intelligent vehicles and mobile robots. Let’s discuss about the obstacle avoidance for a nonholonomic vehicle (mobile robot) like an autonomous wheelchair (Fig. 1). It has two independently driven wheels and a body with a certain shape. If a vehicle can be treated as an omnidirectional movable point, numerous methods have been proposed and applied for it (Fig. 2). Collision free path can be easily found by artificial potential field (Khatib, 1986; Rimon & Koditsuchek, 1992), graph theory (Ulrich & Borenstein, 2000), sensor based method and so on. The problem for a nonholonomic vehicle with two independently driven wheels can come down to that for an omnidirectional point by approximating vehicle’s shape to a circle with the center at the midpoint of two wheels. As shown in Fig. 3, obstacles should be expanded by the radius of the vehicle’s circle and the 26

SCARA Type Robot Arm with Mechanically Adjustable Compliant Joints

A new SCARA type robot arm with passive compliance for contact or constraint tasks is presented. It utilizes a leaf spring and the joint stiffness can be adjusted by rotating this spring, i.e. changing its bending direction. A joint actuator moves an arm link via a connection hollow cylinder and a leaf spring. This mechanism is compact to add in a joint and it can change the stiffness rapidly and stably. We discuss the relationship between the angle of the leaf spring and the joint stiffness and also analyze the relationship between the joint stiffness and the stiffness at the end-effector. Since 4 joints are necessary to make arbitrary stiffnesses in plane motion, a 4 D.O.F. robot arm with proposed compliant joints was developed and tested.

A Powered Wheelchair Controlled by EMG Signals from Neck Muscles

There are many disabled people who cannot handle normal joysticks well; they operate special joysticks by tongue or chin, or they use some voice commands to control powered wheelchairs. A prototype of the powered wheelchair controlled by neck utilize electromyogram (EMG) interface has been developed and tested in this chapter. Head motions of inclining and shaking can be detected from characteristics of neck EMG signals. An operation method by using detected motion types and EMG magnitude of peaks has been also proposed to control a wheelchair smoothly Detection of smaller motions, easier and more reliable operation, control system by face EMG signals are remained for our further works. A wheelchair controlled by EMG interface becomes more useful and reduces users burden, if it has some intelligent support systems to detect/avoid obstacles and to keep running straight in spite of disturbances.

The Effects of Controller Saturation on Dynamic Characteristics of Commercial Positioning Systems and Their Countermeasures

Commercial positioning systems usually consist of several cascade parts, such as a position controller, a velocity controller, a current controller, and an electric motor. Controller design is normally based on linear analysis; however, in practice, controllers frequently drive actuators into saturation, and, sometimes, controllers themselves saturate. Owing to the saturation effect in the servomotor systems, the linear analysis of the servo systems is not sufficient for controller design. Thus, in this paper, the effects of controller saturation on dynamic characteristics of servomotor drivers are investigated by using the numerical simulation; then, the nonlinear position controller for countermeasures of the saturation effects is proposed. The simulation results show that the saturation effect of the controllers degrade frequency responses of the servo system, and make overshoot occur, and they show that the proposed position controller could satisfy fast step responses with no overshoot