Inchworm Motor Research Articles

Ultra-compact, zero-power magnetic latching piezoelectric inchworm motor with integrated position sensor

This paper reports the design, fabrication and characterization of a large-stroke, piezoelectrically actuated linear motor with zero-power latching for portable electronics. The motor consists of a stator having a micromachined piezoelectric actuator and a high-permeability metal guide, a permanent magnet rotor, and an integrated position sensor. The rotor is tethered to the metal guide by magnetostatic attraction due to its permanent magnets. The resulting frictional forces are sufficient to immobilize the rotor to the stator. This does not require any power, and the combined bearing-braking feature is thus termed zero-power latching. The integrated position sensor demonstrates the feasibility of precisely monitoring the rotor position. The completed actuator has a volume of 1 mm(w) × 3 mm(t) × 5 mm(l). With a 50 kHz driving frequency, precision of 5 μm at a scalable full-stroke of 5 mm and a speed of 10 mm/s at 50 kHz was achieved. A capacitive position sensor was also designed into the motor, and was able to determine the rotor position with a sensitivity of 1 fF/μm.

A reusable micromechanical energy storage/quick release system with assembled elastomers

A reusable, elastomer-based energy storage/quick release system for MEMS has been designed, built and tested. Microrubber bands have been fabricated from silicone using two different methods, laser cut and molded, and assembled into silicon microstructures fabricated in a two-mask silicon-on-insulator (SOI) process. Using silicon hooks and force gauges designed in this process, these microrubber bands have been characterized as to their energy storage potential and efficiency by stretching them with a probe tip. These tests showed recovered energy efficiencies up to 92% at strains over 200% with a maximum stored energy over 19 µJ. In addition, a fully integrated micromechanical energy storage system to both store and release energy has been demonstrated using an electrostatic inchworm motor to stretch the elastomer band and release it. Using the inchworm motor, an estimated 4.9 nJ of energy was stored in the elastomer spring and quickly released.

Design and construction of a novel rotary magnetostrictive motor

Magnetostriction can be used to induce linear incremental motion, which is effective in giant magnetostrictive inchworm motors. Such motors possess the advantage of combining small step incremental motion with large force. However, continuous rotation may be preferred in practical applications. This paper describes a novel magnetostrictive rotary motor using terfenol-D (Tb0.3Dy0.7Fe1.9) material as the driving element. The motor is constructed of two giant magnetostrictive actuators with shell structured flexure-hinge and leaf springs. These two actuators are placed in a perpendicular position to minimize the coupling displacement of the two actuators. The principal design parameters of the actuators and strain amplifiers are optimally determined, and its static analysis is undertaken through finite element analysis software. The small movements of the magnetostrictive actuators are magnified by about three times using oval shell structured amplifiers. When two sinusoidal wave currents with 90° phase shift are applied to the magnetostrictive actuators, purely rotational movement can be produced as in the orbit of a Lissajous diagram in an oscillograph, and this movement is used to drive the rotor of the motor. A prototype has been constructed and tested.

Development of probe-to-probe approach method for an independently controlled dual-probe scanning tunneling microscope

We developed a method of fast probe-to-probe approach for an independently controlled dual-probe scanning tunneling microscope (STM), which is essential to measure the transport property of nanostructures, without scanning electron microscopy (SEM). In the approach method, inchworm motors are used as the coarse positioning devices, which are controlled with a personal computer. The method enables an automatic approach of the probe to the other probe within a short time (typically 30 min). After the approach, a real distance between contact points of each probe tip to a sample can be measured from the overlapped part of the STM images obtained with individual probe. The approach method without SEM is also useful to measure the charge transport in the atmosphere, which will be essential for measurement of the bio molecules.

Robot leg motion in a planarized-SOI, two-layer poly-Si process

With the ultimate goal of creating autonomous microrobots, we developed a five-mask process that combines two polysilicon structural layers with 50-/spl mu/m-thick SOI structures and a backside substrate etch. The polysilicon layers provide three-dimensional (3-D) hinged structures, high compliance structures, and electrical wiring. The SOI structural layer yields much stronger structures and large-force actuators. This process was developed as a part of a three-chip solution for a solar-powered 10-mg silicon robot. Here, we describe the fabrication of this planarized-SOI, two-layer poly-Si process (henceforth called the SOI/poly process), basic modules in the design of robot legs in this process, and lastly, the results of fabricated robot legs. In designing the leg structures, we developed guidelines and test structures to provide a better understanding of the robot leg performance. These guidelines include understanding the relationship between the lateral etch depth to the actuator spacing and performing static friction tests of polysilicon flaps to more accurately model the frictional forces of the linkages. Last, we report on the performance of the robot legs and inchworm motors. On an 8 mm /spl times/ 3 mm robot, we have demonstrated a 1 degree-of-freedom (DOF) robot leg, 1 mm in length, which demonstrates up to 60 /spl mu/N of vertical leg force with an angular deflection of almost 30/spl deg/. A two-DOF robot leg, also 1 mm in length, operated with at least 90/spl deg/ of angular deflection, and each inchworm motor demonstrated a shuttle displacement of 400 /spl mu/m with speeds up to 6.8 mm/s. In addition to robot legs, a bidirectional inchworm motor that produces equivalent forces in both directions was also fabricated in this SOI/poly process. This motor uses an additional set of gap-closing-actuator (GCA) arrays to prebias the drive frame.

High-resolution inchworm linear motor based on electrostatic twisting microactuators

A new inchworm micromotor using new electrostatic in-plane twisting microactuators has been designed, fabricated and characterized for nano-resolution manipulators. The proposed twisting mechanism was implemented employing a pair of differential electrostatic actuators with a high stiffness in the driving direction for stable positioning. The electromechanically coupled motion of the voltage–displacement relation was analyzed using a finite element method (FEM), confirming that the twisting actuator makes a tiny step movement efficiently. The proposed actuator was fabricated on a silicon-on-insulator (SOI) wafer with the device footprint of 2.2 × 2.8 mm2, and its nano-stepping characteristics were measured by an optical interferometer consisting of an integrated micromirror and optical fiber. The fabricated inchworm motor showed a minimum step displacement of 5.2 ± 3.8 nm (2σ) and 4.1 ± 2.9 nm (2σ) for cyclic motion in the +y- and the −y-directions, respectively, with the gripping voltage of 15 V and differential voltage of 1 V. As a result, the proposed inchworm micromotor could operate with a stroke of 3 µm and a bi-directional step displacement of less than 10 nm. The step displacement is the smallest value of in-plane-type micromotors so far, and its magnitude was controllable up to 120 nm/cycle by changing the differential voltage.

The Design and Characterization of a Piezo-Driven Inchworm Linear Motor with a Reduction-Lever Mechanism

A piezo-driven inchworm linear motor with a reduction lever mechanism has been designed and characterized. The inchworm motor consists of two clamping devices for gripping a moving shaft and one push-pull device operated by three piezoelectric stacks. To reduce positioning errors caused by control voltage fluctuations and to improve positioning accuracy, a reduction lever mechanism with a monolithic flexure structure is employed to the push-pull device. For the design analysis of the push-pull and clamping devices, their analytical models and equations were developed, by which the static characteristics were evaluated. The positioning performances of the inchworm motor assembled with the push-pull and clamping devices were experimentally characterized. The developed inchworm linear motor proved effective not only in performing a step movement of 1nm up to 82.5nm, with the step size optionally adjusted, but also in providing ultra high positioning accuracy.

Design and characterization of a micromachined inchworm motor with thermoelastic linkage actuators

A new micromachined inchworm motor has been designed, fabricated and characterized for microassembly applications. In order to implement inchworm motions, a pair of thermoelastic actuator is devised to have five-linkage mechanism for two-dimensional motions in tangential and normal directions. The thermoelastic actuators consist of two amplification bars and two coupling bars with four hinge springs. A forked tip located on the apex of the linkage is used to fit the teeth of shuttle mass for its tangential translation. The thermal expansions of the active bars generate the displacement of the actuator, which is then transformed into a bending of the active hinges to be finally amplified by the amplification bar. The inchworm actuator performed the operation at a step movement of 50 μm with a latch-up by the teeth fitting and a driving force of 50 μN for 0.2 μm tolerance.

Single mask, large force, and large displacement electrostatic linear inchworm motors

We have demonstrated a family of large force and large displacement electrostatic linear inchworm motors that operate with moderate to high voltages. The inchworm motor design decouples actuator force from total travel and allows the use of electrostatic gap-closing actuators to achieve large force and large displacement while consuming low power. A typical inchworm motor measures 3 mm /spl times/ 1 mm /spl times/ 50 /spl mu/m and can lift over 130 times its own weight. One motor has achieved a travel of 80 /spl mu/m and a calculated force of 260 /spl mu/N at 33 V. The force density of that motor was 87 /spl mu/N/mm/sup 2/ at 33 V and the energy efficiency was estimated at 8%. Another motor displaced the shuttle at an average velocity of almost 4 mm/s and achieved an estimated power density of 190 W/m/sup 3/. Motors were cycled 23.6 million times for over 13.5 h without stiction. This family of motors is fabricated in silicon-on-insulator (SOI) wafers using a single mask.

A hybrid inchworm linear motor

A hybrid linear motor that produces precise resolution with long travelling distance under inchworm motion principle is developed. The motor consists of one push and two clamping devices. The clamping device is innovated using multistack piezoelectric actuators with displacement amplifier since the displacement generated from multistack actuator is not enough for clamping. To secure the large push load and displacement, Terfenol-D magnetostrictive material is used for the push device. Design process of the push and clamping devices is conducted to meet the performance of the motor. The clamping and push devices are assembled and a control sequence is applied. The performance of the inchworm motor is tested in terms of speed and force. The moving speed is increasing when the input frequency and current are increased. To make the performance stable, time tuning between the push and clamping devices signals is necessary. Some remarks on improving the performance of the motor are addressed.

Development of a compact displacement accumulation actuator device for both large force and large displacement

The design, fabrication, and testing of a compact displacement accumulation device is presented in this paper. The piezoelectric device provides both large displacement (mm) and large force (100 N). The device is based on conventional inchworm motor design that produces large displacement. The device integrates piezoelectric stacks for large force output and high-speed operation with MEMS ridges as a new clamping system. The device should be able to push and pull 450 N at 11 mm/s in a relatively compact size. FEM analysis is used for the design, EDM is used for the fabrication of a prototype, and conventional test techniques are used to evaluate performance. Stress and modal analysis are used to confirm that the device has an infinite fatigue life and a first modal frequency at 1309 Hz. Experimental data for clamping strength of the ridges and blocking force of the device validate that the device transfers the required load of 450 N. The device is successfully tested over a wide range of operating conditions at speeds up to 11 mm/s using open loop control. The stall load of the device is measured to be exceeding 2250 N. For the dynamic loading test, the device pushes test weights up to 50 N with the open loop control approach.

Design and Testing of a Mesoscale Piezoelectric Inchworm Actuator with Microridges

Design and testing of a mesoscale actuator device is presented in this paper. The device uses frequency rectification concepts to amplify the displacements while retaining comparable force outputs to current piezoelectric actuators. The design is based on an inchworm motor with the exception that microridges are used in the clamping system. A FEM model is used to design a device that produces a peak to peak amplitude of 900 N at 11 mm/sec with a weight of 100 g (i.e., specific power of 99 W/kg). Experimental data for piezoelectric stacks and adhesives are used in the design analysis. A prototype device is fabricated and tested with excellent agreement between analysis and testing results. Stress and modal analysis are used to demonstrate that the device has an infinite fatigue life and a first modal frequency at 1777 Hz.

Design, Modeling, and Performance of a High Force Piezoelectric Inchworm Motor

A linear inchworm motor was developed for structural shape control applications. One motivation for this development was the desire for higher speed alternatives to shape memory alloy based devices. Features of the subject device include compactness (60 x 40 x 20 mm), large displacement range (6 mm), and large holding force capability (200 N). There are three active piezoelectric elements within the inchworm: two "clamps" and one "pusher." Large displacements are achieved by repetitively advancing and clamping the pushing element. Although each pusher step is small, on the order of 10 microns, if the step rate is high enough, substantial speeds may be obtained (8 mm/s). In the past, inchworm devices have been used primarily for precision positioning. The development of a robust clamping mechanism is essential to the attainment of high force capability, and considerable design effort focused on improving this mechanism. To guide the design, a lumped parameter model of the inchworm was developed. This model included the dynamics of the moving shaft and the frictional clamping devices, and used a variable friction coefficient. It enabled the simulation of the time response of the actuator under typical loading conditions. The effects of the step drive frequency, the pre-load applied on the clamps, and the phase shifts of the clamp signals to the main pusher signal were investigated. Using this tool, the frequency bandwidth, the optimal pre-load and phase shifts which result in maximum speed were explored. Measured rates of motion agreed well with predictions, but the measured dynamic force was lower than expected.

Characteristics of a piezoelectric miniature motor

The performance of a piezoelectric inchworm motor with a diameter of 4 mm has been evaluated on a miniature scale. The experiments have shown that some of the desired characteristics for a miniature motor such as a high output torque and linear control of rotational velocity with frequency can be achieved using a simple construction. The experimentally measured maximum output torque of 1.4 mN μm is one of the highest presented for a motor of this size. To prevent electrode failure in this first miniature prototype the maximum speed was limited to 4.2 rpm. The most critical parameter for motor performance is height deviations between piezoceramic elements which therefore should be minimised. Further, results show a reasonable agreement with a previously derived analytical model. An optimised motor design is expected to have maximum output torque and speed values as high as 10 mN μm and 120 rpm.

Mesoscale actuator device: micro interlocking mechanism to transfer macro load

A novel proof-of-concept prototype Mesoscale Actuator Device (MAD) containing microscale components has been developed. The MAD is similar to piezoelectrically driven inchworm motors with the exception that mechanically interlocking microridges replace the traditional frictional clamping mechanisms. The interlocked microridges, fabricated from single crystal silicon, are designed to increase the load carrying capability of the device substantially. Tests conducted on the current design demonstrate that interlocked microridges fabricated with 30% KOH solution support a 9.6 MPa shear stress or that a pair of 5×5 mm locked chips supports a 500 N load. For high frequency operation, an open loop control signal is implemented to synchronize the locking and unlocking of the microridges with the elongating and contracting of the actuator. The system was successfully operated from 0.2 Hz to 500 Hz (or speeds from 2 μm/s to 5 mm/s). The upper limit (500 Hz) is imposed by software and hardware limitations and not related to physical limitations of the prototype device.

Designing piezoceramic actuators and motors

Piezoelectric actuators have high energy densities and are capable of producing high force, high bandwidth output. However, they lack the stroke required by many practical applications. Solid-state mechanisms have been designed that utilize flexure hinges to efficiently amplify the stroke of a piezoelectric stack element up to five times. The designs avoid the losses encountered in traditional hinge joints, which are primarily due to tolerance problems, and they minimize losses due to material strain. The mechanisms have been successfully employed in micropositioners for several different applications, including mirror positioners for wavefront compensation and proof mass actuators for vibration suppression. Piezoceramic actuators have also been employed in very high stroke mechanisms: linear and rotary motors. These motors fall into two classes, the ultrasonic motors and the quasistatic type motors. The ultrasonic motors, such as the traveling wave motor, must run at very high frequencies, usually at the resonance frequency of the stator. The quasistatic type motors, such as the inchworm motors, are able to run at low frequencies, but also can be operated at resonance to achieve higher speeds. Both inchworm motors and ultrasonic motors have been successfully demonstrated as prototype devices.

Development of Mesoscale Actuator Device with Microinterlocking Mechanism

A novel proof-of-concept prototype Mesoscale Actuator Device (MAD) is described in this paper. The MAD is similar to piezoelectric driven inchworm motors with the exception that mechanically interlocking microridges replace the traditional frictional clamping mechanisms. The interlocked microridges, microfabricated from single crystal silicon, are shown to support macroscopic loads with exact values dependent upon manufacturing processes. Tests conducted on the current design demonstrate that the interlocked microridges support 16 MPa in shear or that two sets of 3 x 5 mm locked chips support a 50 kgf. Operation of a prototype MAD device containing microridges is accomplished at relatively large frequencies using an open loop control signal. Synchronizing the locking and unlocking of the microridges with the elongating and contracting actuator requires a dedicated waveform in the voltage signal supplied and permitted large operational frequencies. The system was successfully operated from 0.2 Hz to 500 Hz corresponding to speeds from 2,um/s to 5 mm/s. The upper limit (500 Hz) was imposed by software limitations and not related to physical limitations of the current device.

Theory and Applications of Large Stroke Terfenol-D® Actuators

ABSTRACTTraditionally, control algorithms for Terfenol-D® magnetostrictive actuators have modelled the strain as a linear function of magnetic field and stress, but nonlinearity becomes important for strains of more than a few hundred parts per million (ppm), and for many applications even the maximum strain, about 1500 ppm, is inadequate. Larger strokes can be obtained by various types of stroke amplifiers, by resonant operation, or by inchworming. Previously, SatCon successfully used a 10:1 lever arm stroke amplifier in a helicopter flap actuator [1]. Current projects include a water pump using a hydraulic stroke amplifier, which potentially could be more compact and efficient than a lever arm amplifier, and linear and rotary inchworm motors for robotics. In all these designs, satisfactory performance requires careful attention to machining tolerances and to making the mechanisms and housing stiff enough or compliant enough. A model for inchworm motors has been developed, including finite load and resonant effects. Nonlinear control algorithms will be discussed, applicable to arbitrarily large Terfenol-D® strains, stresses, and magnetic fields.

A vibrating reed magnetometer, based on an Inchworm motor and a tunnelling-tip sensor

We have constructed a prototype of a vibrating reed magnetometer with a tunnel junction sensor. Our design uses a single Inchworm motor, controlled by a PC, for both coarse approach and fine positioning. This article discusses the mechanical design of the system, the interface electronics, the software and the preliminary test results.

One approach towards the fabrication of a microrobot system

One approach towards fabrication of a microrobotic system in the nearby future is presented. Three main fields are emphasised: the actuator, the system and the manufacturing technique. The microactuator suggested is a new inchworm motor with bimodal actuator elements. This design compensates for limited fabrication precision of motor elements and simplifies the construction. The realisation of a commercially attractive prototype system is important to the progress of microrobotics. The system suggested here is a teleoperated microrobot arm for applications in biomedicine and in the optoelectronic industry. Hence, the performance demands are given and the components to be integrated in the system can be specified. A modular approach has been taken and adequate components should be: microelectronic chips with serial communication and motor control, inchworm motor components and solid 3D silicon microelements as basic building units. The fabrication technique compatible with the modular construction is 3D hybrid assembly. Six DOF placements in combination with various processing tools are necessary for an arbitrary 3D micromechanical system such as the one suggested. The processing tools might be deposition and machining by a microprobe in a general sense. The basic assembling process will be low temperature bonding. The technique pursued at present is eutectic Au-Si bonding.