Nobuyuki Iwatsuki

Development of a piezoelectric cycloid motor

Abstract Ultrasonic motors have recently been developed which have the advantage over electromagnetic motors that they give high torque at low speed. However, since they are driven by friction between their stator and rotor, they have a problem with wear and, as a result, with the length of useful life. This paper proposes a new piezoelectric cycloid motor, in which the cycloid gear mechanism is used to convert the expansion and contraction of the piezoelectric actuators into the rotational motion of the rotor. Since the motor has no slip motion between its stator and rotor, it is not affected by friction. The fundamental characteristics are theoretically derived, and are examined using a prototype of the motor. The following results are obtained: it rotates steadily and keeps its rotational speed even when the load is increased up to the maximum output torque, 0.014 Nm; the maximum efficiency is 25.5 per cent, which is obtained at 16 rpm within the measuring range of the driving frequency of the motor.

Precision positioning with a rotary-linear motor driven by a pair of 2-D ultrasonic actuators

A new rotary-linear motor is proposed, the spindle of which is driven by a pair of two-dimensional ultrasonic actuators in the axial and rotational directions. A preliminary experiment applying a position feedback control system to a prototype of the motor revealed that a selfinduced voltage of a piezostack reduced the positioning accuracy. An improved control system with a PI controller and an additional RC circuit which compensates the self-induced voltage of a piezostack was proposed and built up. Consequently, step responses with a steady error of 0.007 mm in the axial direction and that of 0.05 degree in rotational direction were achieved.

A ROTARY LINEAR MOTOR DRIVEN BY A PAIR OF TWO-DIMENSIONAL ULTRASONIC ACTUATORS

There is a need to draw various patterns on the inner wall of a small pipe several millimeters in diameter to develop a precise linear scale. Since the authors have already developed a two-dimensional ultrasonic actuator that can move an object is two orthogonal directions independently, they now offer a rotary linear motor, in which the motor shaft is driven by a pair of two-dimensional ultrasonic actuators. Hence, the motor can rotate and move directly, simultaneously, or independently. Good positioning accuracy was obtained for simultaneous two directional drive by controlling the motor with a proportional control: the steady errors were 1.41° and 0.73 mm in the rotary and linear directions, respectively. However, the positioning accuracy greatly decreased for one-directional drive: the steady errors were 27.5° for rotational motion and 20.3 mm for linear motion. To improve these poor positioning accuracies for the one-directional drive, RC series circuits were connected parallel to the piezoelectric devices of a two-dimensional ultrasonic actuator in order to reduce the interference due to the self-EMF induced by the ultrasonic vibration of one pair of piezoelectric devices on another pair. In addition, proportional control was replaced with proportional and integral control. As the result, the positioning accuracy for one-directional drive has been greatly improved, to 0.05° for rotational motion only and 0.006 mm for linear motion only.

Spatial Rolling Contact Pair Generating the Specified Relative Motion Between Links

Link mechanisms with single degree-of-freedom, in which links are connected with only lower pairs cannot completely generate the specified ideal output motion, and dimensional synthesis of them is very complicated. Therefore, we propose the spatial rolling contact pair (SRCP) which can generate the specified relative motion between links, and try to solve the above problems with the proposed SRCP. In order to design the SRCP, a method to specify relative spatial rolling motion between adjacent pairing elements and to determine shapes of both pairing elements which can generate that motion is proposed. An example of the SRCP is then designed and manufactured. The prototype of the SRCP is experimentally confirmed to generate the specified relative motion of pairing element. Finally, a spatial 4-bar mechanism having 1 DOF is synthesized with the SRCP. It can completely generate the specified output motion.

Redundancy optimization of hyper redundant robots based on movability and assistability

This paper describes a new method to utilize redundancy of hyper redundant robots. In order to use redundancy effectively, the contribution of all actuators for the achievement of the target motions and capability for unpredictable target motions in the future should be considered. From this point of view, two evaluation indices, the movability index of each joint and the assistability index for the target motions are proposed. These indices are formulated with the angle and amplitude distribution of the column vectors of Jacobian matrices of each joint, including the end-effector. Then joint input to optimize these indices simultaneously are derived based on the improved gradient projection method. Motion control simulations and experiments with a planar 10R serial manipulator revealed the effectiveness of the proposed method.

Large deformation analysis and synthesis of elastic closed-loop mechanism made of a certain spring wire described by free curves

Recently novel mechanisms with compact size and without many mechanical elements such as bearing are strongly required for medical devices such as surgical operation devices. This paper describes analysis and synthesis of elastic link mechanisms of a single spring beam which can be manufactured by NC coiling machines. These mechanisms are expected as disposable micro forceps. Smooth Curvature Model(SCM) with 3rd order Legendre polynomial curvature functions is applied to calculate large deformation of a curved cantilever beam by taking account of the balance between external and internal elastic forces and moments. SCM is then extended to analyze large deformation of a closed-loop curved elastic beam which is composed of multiple free curved beams. A closed-loop elastic link is divided into two free curved cantilever beams each of which is assumed as serially connected free curved cantilever beams described with SCM. The sets of coefficients of Legendre polynomials of SCM in all free curved cantilever beams are determined by taking account of the force and moment balance at connecting point where external input force is applied. The sets of coefficients of Legendre polynomials of a nonleaded closed-loop elastic link are optimized to design a link mechanism which can generate specified output motion due to input force applied at the assumed dividing point. For example, two planar micro grippers with a single pulling input force are analyzed and designed. The elastic deformation analyzed with proposed method agrees very well with that calculated with FEM. The designed micro gripper can generate the desired pinching motion. The proposed method can contribute to design compact and simple elastic mechanisms without high calculation costs.

Micro Cilium Actuators in Group

Aiming to realize novel micro mobile robots or micro conveyers, artificial micro cilium actuators in group should be developed. A pipemorph actuator which is composed of a thin needle as an internal electrode, piezoelectric thin film cylindrically surrounding the internal electrode, and external electrodes attached on the orthogonal four surfaces of the piezoelectric film is adopted as an artificial cilium and then the effective processes based on the hydrothermal method the and electrostatic flocking to fabricate the micro pipemorph actuators in group are proposed and experimentally examined. The cilium actuators in group which are fabricated by using partial nickel plating of titanium wire can convey small paper sheets or plastic sheets at the maximum speed of 1.53 µm/min.

Dexterity Evaluation and Optimization of Hyper Redundant Robots Based on Movability and Assistability

This paper describes a new method to utilize redundancy of hyper redundant robots. To achieve dexterous motion of hyper redundant robot, joint inputs should be determined by taking account of i.e., the contribution of all actuators for the achievement of target motions and capability for unpredictable target motions in future is necessary. Two evaluation indices, the movability index of each link and the assistability index for target motion, are thus formulated with the angle distribution of column vectors of Jacobian matrix for each link. Then joint input to maximize or minimize these indices are derived based on an improved gradient projection method. The physical meaning of the proposed indices is also discussed by comparing with conventional manipulability measure. Motion control simulations and experiments with a planar 10R serial manipulator revealed the effectiveness of the proposed method.

The Estimation of the Sound Power Radiating from a Peripherally Fixed Rectangular Plate Subjected to Acoustic Excitation (2nd Report, Estimation and Experiment in Case the Plate is Excited in Diffused Sound Field)

This paper describes the estimation method of the sound power radiating from a four side fixed rectangular plate acoustically excited in a diffused sound field. First, the forced vibration of the plate excited by a plane wave in a free sound field has been solved. In the calculation, the distribution of the plane angles of modal exciting forces is taken into consideration precisely. Next, the stochastic model composed of random plane wave elements is assumed on the diffused sound field. The modal exciting forces and the forced vibration displacement are derived based on the ergodic process. Using the obtained forces and displacement, the equations for calculating the frequency spectra of the parameters for estimation are derived. The estimated frequency responses of radiating sound power coincided well with the measured values.

Real-time measurement of in-plane vibration by double-aperture laser speckle interferometry

This paper describes the real-time measurement of in-plane vibration using an improved double-aperture laser speckle interferometer. To detect the in-plane vibration in real- time, a new signal processing system which can detect the phase angle of the frequency component of the interference fringes in real-time by calculating Fourier coefficients is proposed. The proposed real-time signal processing system is composed of a pulse generator, a sin/cos generator and an A/D converter controlled by a personal computer, and of an analog electronic circuit made of analog ICs. The linearity of the output signal of the prototype due to a number of the detected fringes and noises is experimentally examined. In- plane static displacement and vibration displacements of a specimen driven by a piezostack are measured with a new laser speckle interferometer equipped with the proposed signal processing system and are calibrated with a gap sensor. The measured static in-plane displacements varied in proportion to the given displacement with reproductive error variation with the maximum value of 0.5 micrometers . The vibration displacements measured with the laser speckle interferometer were detected with the maximum sampling frequency of 470Hz. This new laser speckle interferometer thus achieved the measurement of in-plane vibration in real-time.