Optimization of gear ratios for dual-motor actuators is presented for the development of a walker-type assist robot. The robot is reconfigurable to provide an elderly user with multiple physical support functions; one is to assist sitto-stand transitions and the other is to serve as a walker to aid the user in walking. To avoid falling while walking, the robot must react quickly and reconfigure its footprint for supporting the user. This requires high speed actuators. In contrast, for assisting sit-to-stand transitions, high torque actuators are required. To meet the bimodal, conflicting load conditions, i.e. high-torque, low-speed v.s. high-speed, low-torque, this paper presents a dual-motor actuation solution, where two motors with diverse gear ratios are combined. The system is characterized with two key parameters: an internal gear ratio between a high-speed motor and a torque-booster, and an external gear ratio for connecting the dual motor actuator to the load. The internal and external gear ratios are optimized for performing both sit-to-stand assist and rapid foot reconfiguration.

Inspection and maintenance of equipment inside buildings, such as exit signs, bared pipelines, air vents, and fire alarms often requires a robot to reach high, hidden, or confined areas that are difficult for humans to access. Even though these tasks are easy and repeatable, they are still not automated. The Mobile Extendable Robot Arm (MERA) is a movable robot arm with a novel 2-DOF scissor mechanism for reaching a high place and positioning an end-effector. MERA is composed of a locomotion vehicle with a rotation table and a 4-DOF extender arm, itself made of two layers of the 2-DOF scissor mechanism arranged in series. Placing the end-effector at an arbitrary point in space, the 4-DOF arm possesses two degrees of redundancy, allowing access to a point from various directions and enabling obstacle avoidance. In this paper, we present the design and analysis of the 2-DOF scissor mechanism. The 2-DOF scissor mechanism has two rotary actuators for driving the base links individually; consequently, the mechanism can elongate the entire body and tilt at the center of the base shaft. However, we found that the 2-DOF scissor mechanism had a singularity; after analyzing the singularity, we propose two novel solutions to the problem.

A novel design concept of expandable robotic arm inspired by plant growth is presented. The robot can construct its own structure by converting a type of fluidized material into a rigid structure at its growing point. The robot can extend its structure in multiple directions, and move through a winding space to reach a point, which is otherwise difficult to access. The robot with the rigid structure can also bear a significant load, has a plate to attach an end-effector, and can transport an object. The robot satisfies three key functional requirements that are characteristic to plant growth. First, the robot is capable of transporting structural materials to its growing point. Second, the robot is capable of transforming the material into a rigid structure. Third, it is capable of steering its growing point so that it is expanded in a desired direction. A proof-of concept prototype is then presented that consists of a special sprocket chain that can be switched between flexible/fluidized and rigid states, a winch that can pull/transport the chain, and a steering system to direct the growing direction. Unlike plants, this growing robot can retract its extended body, and can extend in a different direction. The prototype demonstrates that it meets all the functional requirements, and that it can make sharp turns and move through obstacles.

Tactile sensors for slip detection are essential for implementing human-like gripping in a robot hand. In previous studies, we proposed flexible, thin and lightweight slip detection sensors utilizing the characteristics of pressure-sensitive conductive rubber. This was achieved by using the high-frequency vibration component generated in the process of slipping of the gripped object in order to distinguish between slipping of the object and changes in the normal force. In this paper, we design a slip detection sensor for a multi-fingered robot hand and examine the influence of noise caused by the operation of such a hand. Finally, we describe an experiment focusing on the adjustment of the gripping force of a multi-fingered robot hand equipped with the developed sensors.

Slip-detecting tactile sensors are essential for achieving human-like gripping motion with a robot hand. In previous research, we developed a flexible, thin and lightweight slip sensor that exploits the characteristics of pressure conductive rubber. However, using this sensor, it was difficult to distinguish between object slip and a change in the normal force. Therefore, in the present research, we investigated a method for identifying object slip by analyzing the frequency components of the output signal from the sensor. As a result, we found that high-frequency components of 1 kHz or more are included in the complex voltage signal generated by object slip. Therefore, by using this high-frequency component, we developed a simple sensor that distinguished between both contact and initial slip with high sensitivity.

Even with the eyes closed, humans are able to grip an object with minimal force without such information as the coefficient of friction or the weight. Tactile sensors capable of detecting slippage are necessary for this gripping action to be realized in a robot hand. Heretofore, many slip sensors were developed and produced, but there was not a slip sensor of simple structure practical for installation on fingertips of a robot hand. Therefore, we propose a low-profile/lightweight slip sensor of simple structure. The special properties of pressure conductive rubber are utilized as a detection device in this sensor. In this paper, we discuss the results of trial manufacture and of slip detection property testing of this sensor. Moreover, we will report the results of slip prevention experiments by this prototype slip sensor, and indicate that the pressure conductive rubber is promising as a material of slip sensor.

To achieve a human like grasping with a multi- fingered robot hand, the grasping force should be controlled without using information from the grasped object such as its weight and friction coefficient. In this study, we propose a method for detecting the slip of a grasped object using the force output of Center of Pressure (CoP) tactile sensors. CoP sensors can measure the center position of a distributed load and the total load applied on the surface of the sensor, within 1 ms. These sensors are arranged on the fingers of the robot hand, and their effectiveness as slip detecting sensors is confirmed in tests of slip detection during grasping. Finally, we propose a method for controlling grasping force to resist tangential force applied to the grasped object using a feedback control system with the CoP sensor force output.

Slip detecting tactile sensors is essential to achieving a human-like gripping motion with a robot hand. Up until now, we have developed flexible, thin and lightweight center of pressure (CoP) sensor. The sensor, constructed of pressure conductive rubber sandwiched between two sheets of conductive film, is able to detect the center position of the load distribution and the total load. Recently, detection of initial slip has been shown to be possible. However the detection principles are unclear. Therefore, we carried out verification experiments of the slip detection properties of the CoP sensor and the detection principle. In the results, we found a change in electrical conductivity produced with a shear deformation of the pressure conductive rubber. In this paper, we will discuss the slip detection properties of the CoP sensor and detection principle.

A tactile sensor is developed with the aim of covering a robot’s entire structure, while reducing wiring requirement and ensuring high-speed response. The sensor detects the center point of load distribution on 2-dimensional surfaces as well as the overall load. There are only 4 signal wires from the sensor. The sensor response time is nearly constant (within 1ms) regardless of the number of detection elements, their placements or sensor areas. In this paper, the principles behind the operation of this sensor and the results of experiments using the sensor are described. Further, a developed tactile element composed of pressure-sensitive materials and chip-resistors is described.