A previously developed passively operating transmission capable of switching its reduction ratio in response to load torque was further developed into a non-contact load-responsive transmission. The reduction ratio is switched by a non-contact magnetic clutch that responds to the load torque using a passive magnetic mechanism without any accessory actuators, sensors, electronics or power supplies. The absence of mechanical friction at the non-contact magnetic clutch resolves the problems concerning the wear and maintenance, shock while switching the clutch is greatly reduced and the actuator is protected from overloads by slippage at the magnetic clutch. This non-contact load-responsive transmission reduces the power, size and weight of the mechanical system and improves its safety and agility since a variant load can be actuated efficiently using a minimal actuator. This paper describes the structure and the operation of the non-contact load-responsive transmission and reports on the characteristics of an experimentally evaluated prototype transmission.

A passively operating load-responsive transmission capable of switching the reduction ration in response to load-torque was developed. When the load torque is low, the transmission operates with a low reduction ratio that enables the actuator to rotate a high-speed and low-torque load efficiently. When the load torque increases, the transmission switches to a high reduction ratio to rotate a low-speed and high-torque load. The reduction ratio is switched by a pair of clutches connected and disconnected separately. These clutches are passively operated by the magnetic mechanism that exerts thrust in alternative direction responding to the load torque without any accessory actuators, sensors, electronics or power supplies. The load-responsive transmission can reduce power, size and weight of the mechanical system and improve its safety since a variant load can be actuated efficiently by a minimal actuator. In this paper, the advantages and requirements of the load-responsive transmission are first outlined followed by the structure and the operation of the developed transmission. Further, the characteristics of a prototype transmission are experimentally evaluated.

A microfactory is a new concept for an extremely miniaturized manufacturing facility that enables dramatic space and energy conservation. As a material transfer and assembly component of a prototype microfactory, a micro transfer arm that provides 4-DOF and a maximum length of approximately 100 mm has been developed. To achieve a compact-lightweight structure, large workspace and high positioning accuracy, the arm is configured as a combination of a SCARA-type manipulator and a parallel mechanism. To enable the arm to perform fine assembly tasks, a 3-axis device with an integrated passive compliance device and force sensor was developed. In this paper the mechanical design of the arm structure and the fabrication process of the device are described, followed by an experimental evaluation for the arm and device.

A haptic display for grasping and manipulating virtual objects in a CAD environment is investigated for the development of rapid prototyping technology. The operator receives the sensation of contacting and tracing of the surface of the virtual object, and of grasping and manipulating the object from the haptic display. After the control of the haptic display is formulated, it is implemented on the Sarcos Dexterous Arm Master. The proposed haptic display is experimentally confirmed to provide realistic sensation that enables the operator to grasp and manipulate the virtual object easily as intended.

The kinematics, statics and stiffness effect of a 3D grasp by a multifingered hand is investigated considering the rolling contact at the fingertip. By representing the local shape of the fingertip and the object by a quadratic surface and by linearization of the fundamental formulae, the kinematic-static relation for the motion-force of the fingertip, contact location and the object is derived. Additionally, the stiffness effect for object motion that affects the stability of the grasp is analyzed and evaluated for the grasp by a three-fingered hand.

Dynamic grasping force control for a multifingered hand is proposed and investigated. The grasping force of the finger is dynamically adjusted according to the tactile feedback so that each fingertip force always stays inside the friction cone detected by the tactile sensor and the fingertips maintain firm contact without any undesired slip no detaching from the surface of the object while grasping it. The proposed method can be applied for real-time control of the hand since it requires few numerical calculations. The validity of the proposed method is experimentally confirmed using a two-fingered hand with finger-shaped tactile sensors.

Curvature is a useful feature for characterizing arbitrary smooth 3-D surfaces. This paper describes our study of detecting object curvature using tactile sensing. Using the constraints on the relative motion between two bodies in contact, the curvature of an object can be obtained by inducing a relative differential motion and sensing the change in the location of contact. To understand the limitation of the practical application of this approach, sensitivity of the curvature estimate to errors in sensory data is presented. The validity of the theoretical development is examined experimentally using an optical wave-guide based tactile sensor and one finger of a three-finger dextrous hand. A good agreement between the theoretical analysis and the experimental results has been obtained.

A novel framework for dextrous manipulation planning based on transformations between canonical grasp configurations is proposed in this paper. The proposed approach is inspired by the observation that human hand is capable of a large number of manipulative tasks with a few finger postures or grasps. It is postulated that the key to the control of manipulation tasks, therefore, lies in the combination of these grasps. The proposed framework first identifies important or canonical grasps, defined in terms of contact pairs between topological features of the hand and the object, and then obtains the possible transitions between the grasps. With the result expressed in the form of a grasp transformation graph, general manipulation tasks can then be planned by searching the graph for a path connecting the initial and final configurations of the tasks. The proposed approach is demonstrated by experiments using a three-finger hand performing object manipulation tasks.

A new motion control system using tactile feedback is investigated for the manipulation of an object by a multifingered hand where the fingertips and the object make rolling contact. The proposed control system is capable of determining the motion of fingers so that the hand manipulates the object along the desired trajectory according to the tactile feedback at the fingertip. The advantage of the algorithm developed here is that geometrical information about the object to be manipulated is not necessary and therefore the algorithm can be applied to the manipulation of an unknown object. First, a mathematical model of the kinematics of the manipulation with rolling contact at the fingertip is formulated. Next, a trajectory planning algorithm for the fingers is derived. Finally, the previously developed finger-shaped tactile sensor using an optical waveguide is installed on the two-fingered hand, and the superiority of the proposed algorithm is demonstrated through computer simulations and experiments.

The authors discuss active tactile sensing for detecting a contact point between a multifingered robot hand and an unknown object. They define the concept of actively sensible meaning that an active sensing motion can be planned for a sensing event. Assuming more than two sensing events, conditional-minimum-external-sensor-realization is defined, where it is shown that it is possible to reduce the number of external sensors with a well-planned sensing algorithm. Based on these definitions, an active sensing algorithm for detecting the contact point with minimum-external-sensor-realization is proposed. This approach remedies several disadvantages found in conventional approaches. The approach was tested through experiments using a single-finger model with a fingertip tactile sensor.>

A finger-shaped tactile sensor previously reported in a scaled-up version was miniaturized and its signal processing speed improved. The miniaturized tactile sensor consists of a hemispherical optical waveguide with an elastic cover, a fiber-optics plate (FOP), a position-sensitive detector (PSD), and infrared light-emitting diodes (LEDs) for the light source. When an object comes in contact with the sensor, the elastic cover is depressed and light from the LEDs, which normally maintains total internal reflection within the waveguide, is scattered at the contact location of the waveguide and the cover. The scattered light is transmitted to the PSD through the FOP. The contact location and the normal to the surface of the object are determined from the output of the PSD. The sensor's fundamental characteristics were evaluated through experiments using the miniaturized version. The sensor was installed at the tip of a robotic finger to create an active touch system. By combining tactile sensing and motion control of the finger, the profile of an unseen object was successfully delineated.>

Abstract — We investigate manipulation and active sensing by a pushing control system using only tactile feedback. The equations of motion of a pushed object are derived using a model of the object’s limit surface, and we design a control system to translate and orient objects. The effectiveness of the proposed controller is confirmed through simulation and experiments. Active sensing of the object’s center of mass is described. I.

A method of compliance control for ai redundant manipulator was proposed. The method is constructed by combining two different compliance control schemes; the fundamental compliance control in the joint space and the adjusting compliance control in the operational space. One of the features of the proposed method was the achievement of both the desired compliance condition in the operational space and the unique determination of the redundant manipulator configuration. Another feature of the method is that the inverse kinematic solution of the redundant manipulator was obtained only according to fundamental compliance parameters. Also, the determination of how to control the trajectory of the end- effector was introduced. The inverse kinematics solution is similarly obtained from the pseudo- inverse Jacobian matrix with a weight matrix. However, it has a different benefit from the pseudo-inverse approach, because it provides a function of adjusting the end-effector compliance as well as the inverse kinematics solution. Through experiments using a manufactured four degrees-of-freedom robotic arm which allowed redundancy, the efficiency of the method was confirmed.

The authors discuss force control for the tendon-sheath driving system typically used to actuate robotic finger joints. For a simple tendon-sheath model, the transmission characteristics were first formulated with factors called the apparent tendon stiffness and equivalent backlash. An interesting aspect is that apparent tendon stiffness changes when the tendon is pulled or loosened, while tendon stiffness itself keeps constant under the absence of friction. This unexpected behavior is confirmed by simulations as well as experiments. The authors also consider the effect of apparent tendon stiffness on force control and show that the direction-dependent behavior of apparent tendon stiffness eventually brings about a direction-dependent response in the force control system.>