Showing papers on "Actuator published in 1990"

Engineering Aspects of Shape Memory Alloys

Abstract: An introduction to martensite and shape memory, CMWayman and TWDuerig shape memory and transformation behavior of mariensitic Ti-Pd-Ni and Ti-Pt-Ni alloys, PGLindquit and CMWayman the mechanical aspects of constrained recovery, JLProft and TWDuerig the design of electrical interconnection systems with shape memory alloys, ECydzik actuator and work production devices, AKeeley, DStockel and TWDuerig fatique of copper-based shape memory alloys, EHornbogen shape memory actuators for automotive applications, DStockel using shape memory for proportional control, DEHodgson an engineer's perspective of pseudoelasticity, TWDuerig and GRZadno the use of superelasticity in guidewires and arthroscopic instrumentation, JStice some notes on the mechanical damping of shape memory alloys, MWuttig

Positive position feedback control for large space structures

Abstract: A new technique for vibration suppression in large space structures is investigated in laboratory experiments on a thin cantilever beam. This technique, called Positive Position Feedback, makes use of generalized displacement measurements to accomplish vibration suppression. Several features of Positive Position Feedback make it attractive for the large space structure control environment: The realization of the controller is simple and straightforward. Global stability conditions can be derived which are independent of the dynamical characteristics of the structure being controlled, i.e., all spillover is stabilizing. The method cannot be destabilized by finite actuator dynamics, and the technique is amenable to a strain-based sensing approach. The experiments control the first six bending modes of a cantilever beam, and make use of piezoelectric materials for actuators and sensors, simulating a piezoelectric active-member. The modal damping ratios are increased by factors ranging from 2 to 130.

Modelling of Piezoelectric Actuator Dynamics for Active Structural Control

Abstract: The paper models the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect. The coupled equations of motion of an arbitrary elastic structure with piezoelectric elements and passive electronics are derived. State space models are developed for three important cases: direct voltage driven electrodes, direct charge driven electrodes, and an indirect drive case where the piezoelec tric electrodes are connected to an arbitrary electrical circuit with embedded voltage and current sources. The equations are applied to the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.

Modal Sensors/Actuators

Abstract: A piezoelectric laminate theory that uses the piezoelectric phenomenon to effect distributed control and sensing of structural vibration of a flexible plate has been used to develop a class of distributed sensor/actuators, that of modal sensors/actuators. The one-dimensional modal sensors/actuator equations are first derived theoretically and then examined experimentally. These modal equations indicate that distributed piezoelectric sensors/actuators can be adopted to measure/excite specific modes of one-dimensional plates and beams. If constructed correctly, actuator/observer spillover will not be present in systems adopting these types of sensors/actuators. A mode 1 and a mode 2 sensor for a one-dimensional cantilever plate were constructed and tested to examine the applicability of the modal sensors/actuators. A modal coordinate analyzer which allows us to measure any specific modal coordinate on-line real-time is proposed. Finally, a way to create a special two-dimensional modal sensor is presented.

Micro/miniature shape memory alloy actuator

Abstract: Shape memory alloy (SMA) has great potential for microminiature actuators. The feasibility is discussed, and theoretical estimates based on scale effect are presented. Control schemes for microminiature SMA servoactuators are discussed, and a control scheme is proposed. Combined with electric resistance feedback and position feedback, it enables the author to control stiffness of SMA directly and to sense force without a force sensor. Experimental verifications are reported. The application of a miniature SMA actuator to a miniature clean gripper with position-force hybrid control for microelectronics manufacture is presented. Fabrication of a thin film micro SMA actuator is investigated. >

Programmable tactile stimulator array system and method of operation

Abstract: A tactile stimulator array system and method of operational incorporating a plurality of tactile elements having touch-stimulating portions which are positioned through corresponding openings formed in a touch plate The tactile elements are moved by actuator wires which are formed of a shape-memory alloy material Electrical control signals from a programmed computer system heat individual wires through the materials phase change transition temperature so that the wires contract to their memory shapes and raise the elements The touch-stimulating portions then extend above the touch plate where they can be sensed by the user

Heat-activated drug delivery system and thermal actuators therefor

Abstract: A thermal actuator, also known as a heat capacitance motor, derives its energy from the physical expansion of paraffin wax as it changes from solid to liquid when heated within an enclosure such as a cylinder. This energy is converted into mechanical force which causes translation of a piston slidably mounted within the cylinder, thus creating hydrostatic pressure which is converted to work. The thermal actuator may be utilized in various drug delivery systems in which the hydrostatic pressure created by the actuator is used expel the contents of a syringe.

Electronic range of motion apparatus, for orthosis, prosthesis, and CPM machine

Abstract: A therapeutic electronic range of motion apparatus includes a remote subsystem for generating motion commands which are transmitted to a local subsystem at an orthosis, prosthesis or CPM machine. The local subsystem includes a local controller for controlling and monitoring the position, speed, and direction of an actuator which moves an orthotic brace, prosthesis or CPM machine mounting. The apparatus is programmable enabling a patient to program stopping positions which thereafter are selectable by command. When the actuator is not in motion the local controller enters a sleep mode to conserve power. The controller is automatically awakened when a motion command is received.

Design Principles for Vibration Control Systems Using Semi-Active Dampers

Abstract: Electronically controlled vibration isolation and control systems have recently reached at least the prototype phase in a number of fields of application. Of particular practical interest are semi-active systems which require very little actuator power. Semi-active dampers in the form of rapidly modulated hydraulic shock absorbers have been used for example in automobile suspensions to achieve some of the benefits of fully active servo-mechanism systems but with much reduced cost and complexity

A micro-positioning tool post using a piezoelectric actuator for diamond turning machines

Abstract: A micro-positioning tool post ‘Piezo tool servo’ has been developed for high-resolution tool servo systems for ultra-precision diamond turning machines. It was designed by using a wire-cut parallel spring mechanism, a PZT stack actuator and a capacitance gauge. To eliminate the non-linearities in the PZT actuator and to improve the stiffness and response, two types of closed-loop controller were applied to the tool post, and compared. Both controllers were effective in obtaining flat frequency characteristics, resolution, static stiffness and static stability. The actual resolution of depth-of-cut control was determined by a cutting test on an aluminium alloy.

Multiple actuator disk drive

Abstract: A multiple actuator disk drive (20) utilizes multiple heads (46a-j, 47a-j) associated with respective ones of multiple actuators (341, 342) to read data from and write data to all tracks on the surface of a disk. The positioning of each head by the respective actuators is controlled by embedded servo-information recorded in the data tracks. The data tracks have a density of greater than 2000 tracks per inch. Utilizing two actuators provides access times which are reduced with respect to the access times provided by disk drives having a single actuator and an increased data transfer rate.

Apparatus for driving a piezoelectric actuator

Abstract: An apparatus (200) is provided for controllably connecting and disconnecting a piezoelectric actuator (205) to and from an energy source (210) to effect the displacement of a piezoelectric actuator (205) for a fuel injector. Precise control of the timing and duration of the piezoelectric actuator (205) is necessary to ensure that a proper quantity of fuel is delivered to each cylinder of an internal combustion engine. A charging and discharging means (235, 240) monitors the voltage level of the piezoelectric actuator (205), and the charging and discharging current of the piezoelectric actuator (205). Further, a smoothing means (245) aids in levelling the charging and discharging current to better approximate a constant current to control the piezoelectric actuator (205) providing a precise quantity of fuel to be delivered.

Multi-layered electrostatic film actuator

Abstract: A multilayered electrostatic film actuator to realize a high force/weight ratio actuator applicable for large-scale machines is proposed. It has numerous films with plenty of small electrodes stacked and connected. In order to build this structure, an electrostatic actuator named the image charge stepping actuator has been developed. It utilizes image charges induced on a high resistance to produce force. It is fabricated on polymer films and a prototype of the multilayered actuator with four film actuators has been constructed. The fabricated multilayered actuator can produce a force of 0.4 N. >

Actuator Properties and Movement Control: Biological and Technological Models

Abstract: Actuation is the process of conversion of energy to mechanical form. A device that accomplishes this conversion is an actuator. There are many types of actuators, with most including energy transformation through multiple forms. Of course an equally vital part of the definition of an actuator is controllability: the actuator’s conversion of energy must be modulated by a control input.

Photostrictive actuator

Abstract: It has been demonstrated that PLZT ceramics exhibit large photostriction under optical irradiation, and are applicable to photostrictive actuators. Photo-driven relays and micro-walking machines have been developed, which are designed to start moving under irradiation and have neither electric lead wires nor electric circuits. >

Thermal compensated head positioner servo for disk drive

Abstract: Thermal compensation is provided to a seek mode servo loop of a disk drive having a head and disk assembly including a spindle motor for rotating at least one data storage disk and an electromechanical actuator structure for positioning a data transducer head relative to concentric data tracks defined on a data surface of the data storage disk. This method comprises the steps of: sensing temperature of the head and disk assembly dynamically during operation of the disk drive, calculating a multiplication factor as a function of sensed temperature, multiplying the multiplication factor by a reference velocity command during a track seek operation to provide a velocity command, comparing the velocity command with a fed back velocity value to generate a velocity error signal, and applying the velocity error signal to an actuator driver to control operation of the actuator structure during the track seek operation.

Accurate Position Control of a Pneumatic Actuator

Abstract: We propose a new control strategy for on-off valve controlled pneumatic actuators and robots with focus on the position accuracy. A mathematical model incorporating pneumatic process nonlinearities and nonlinear mechanical friction has been developed to characterize the actuator dynamics; this model with a few simplifications is then used to design the controller. In our control scheme, one valve is held open and the other is operated under the pulse width modulation mode to simulate the proportional control. An inner loop utilizing proportional-plus-integral control is formed to control the actuator pressure, and an outer loop with displacement and velocity feedbacks is used to control the load displacement. Also, a two staged feedforward force is implemented to reduce the steady state error due to the nonlinear mechanical friction. Experimental results on a single degree of freedom pneumatic robot indicate that the proposed control system is better than the conventional on-off control strategy as it is effective in achieving the desired position accuracy without using any mechanical stops in the actuator.

Servo/data actuator arm flexible circuit

Abstract: An improved multilayer flexible circuit for use in a disk storage device actuator arm supporting a data head and a servo head includes a first ground plane and a second electrically floating ground plane.

Shape memory actuator

Abstract: A shape memory actuator for controlling the position of a control member, such as a damper plate in a duct, the actuator including first and second shape memory elements each having an austenite phase transition temperature above which each element assumes a predetermined memory shape and a lower phase which forms when said element is stretched from the predetermined memory shape, the first and second elements being connected to move the control member in different directions when one or the other of the elements are heated to a temperature above its austenite phase transition temperature and an electrical circuit for selectively raising the temperature of one or the other of the elements. The control member may be held in a position between full open and full closed by holding mechanisms which connect the actuator to the control member. The holding mechanisms include a visco elastic mechanism, a positive interlock mechanism that is released by a shape memory element, or a magnetic member formed of alternately arranged magnetic poles. A number of connectors are disclosed for connecting the SMA members to the dampers.

The Positioning of Sensors and Actuators in the Vibration Control of Flexible Systems

Abstract: A method is presented for the determination of sensor and actuator positioning and feedback gains for the active vibration control of flexible structures. This method is based on the minization of the minimum quadratic cost functional in the standard optimal control. The optimal criterion is determined via Riccati equations, and it is minimized with a recursive quadratic pfogramming algorithm with respect to sensor and actuator positioning parameters. The application of this method to a cantilever beam yields several dislocated sensor and actuator locations which are locally optimal. An extension to a case in which modal filters are used is also examined. In this case, the location of the actuator is found to be more sensitive than that of the sensors. This method has clear physical meaning and the flexibility to allow varying of the weighting matrix.

Automated dispensing apparatus

Abstract: Dispenser actuating apparatus includes guide rails carrying a valve actuator at one end. A pump actuator is mounted for sliding along the guide rails, and the guide rails are mounted for sliding along their central axes. Separate motors and drive belts reciprocate the valve and pump actuators with independent movements.

On the nature of the interaction between structures and proof-mass actuators

Abstract: This paper presents an analysis of the interaction between a structure, an actuator used to control the vibration of the structure, and the control law to be implemented by the actuator. The control hardware used is a proof-mass actuator with experimentally verified dynamics capable of being used in a space structure configuration. A local rate-feedback control law is used. The control of two different structures is presented. The first structure is a cantilevered beam constructed of a quasi-isotropic composite material that is controlled by a single actuator forming the experimental component of the investigation. The second structure is a finite-element model of a truss system controlled by a single actuator. Models of both structures predict the presence of potential instabilities in system performance if proper consideration is not given to interactions between the control law, the structure, and the actuator.

Distributed type of actuators by shape memory alloy and its application to underwater mobile robotic mechanism

Abstract: The basic idea of a new type of actuator based on a shape memory alloy (SMA) and its application to underwater mobile robots are presented. The actuator consists of a multimode SMA, so that any shape can be produced as the synthesized sum of excited modes. Thus, the actuator shows the characteristics of distributed-parameter-type actuators with a specified number of modes. A flat-belt-type SMA is employed, and its bending characteristics are examined. A method of waveform synthesis is presented. Applying the proposed distributed actuators to the underwater mobile robot, a fish-fin-like mechanism is shown to obtain thrust forces in the water. The shape of the actuator was shown experimentally to be similar to the computed shape. As a result, the distributed actuator shows the possibility of application to distributed-parameter shape control. >

Robust near time-optimal control

Abstract: A robust control algorithm for a realization of nearly time-optimal control of double integrator plants is presented. The technique involves the combination of traditional bang-bang time-optimal control with the methods of sliding-mode control. The result is a nonlinear feedback scheme for maintaining a desired functional relationship among dynamic variables, in this case imitating the idealized dynamics of time-optimal control. The approach is nearly time optimal rather than exactly time optimal, since the bang-bang control components are restricted to values below full actuator saturation, thus reserving some actuator effort for compensation of disturbances and model imperfections. The algorithm blends smoothly into a linear controller near a stable goal location. >

Sensor and actuator selection for large space structure control

Abstract: This paper presents an algorithm that aids the controls engineer in specifying a sensor and actuator configuration for regulation of large-scale, linear, stochastic systems such as a large space structure model. The algorithm uses a linear quadratic Gaussian controller, an efficient weight-selection technique based on successive approximation, and a measure of sensor and actuator effectiveness to specify a final sensor and actuator configuration. This configuration enables the closed-loop system to meet output specifications with minimal input power. The algorithm involves no complex gradient calculations and is numerically tractable for large linear models, as demonstrated by the solar optical telescope example in this paper. Additionally, the algorithm provides the controls engineer with information on the important design issues of actuator sizing, reliability, redundancy, and optimal number. HE advent of the Space Shuttle makes the large space structure (LSS) an imminent reality. These future space structures will be measured in kilometers and, of necessity, will be lightweight and highly flexible (light damping). Standard LSS missions will include power generation, surveillance, astronomy, and communications. These missions will require stringent pointing accuracy, shape control, and vibration suppression. To satisfy these demanding mission requirements, the LSS will almost certainly require an active, regulator-type controller with multiple sensors and actuators located throughout the structure.i-6 Furthermore, given the size of an LSS, there will be a large set of admissible sensor and actuator locations. The controls engineer then faces the problem of selecting a limited number of sensor and actuator locations to "best achieve" the LSS mission. The term "best achieve" in this paper means achieving the LSS output specifications with minimal actuator power. The solution to this sensor and actuator selection (SAS) problem needs at least the following ingredients: 1) A specific closed-loop control law structure; 2) a technique for systematically adjusting (tuning) control law parameters to achieve output specifications with minimal power; and 3) a technique to evaluate the effectiveness of possible sensor and actuator configurations in achieving output specifications with minimal power. This paper incorporates the preceding ingredients into an algorithm that solves the SAS problem for an LSS modeled as a linear stochastic system. Some necessary background information on linear stochastic systems and linear quadratic Gaussian (LQG) control theory are presented in Sec. II along with a formal statement of the SAS problem. Section III contains two important selection theorems, four pertinent facts, and the general flow of the SAS algorithm. Results from the SAS algorithm applied to the controller design for a large space telescope are presented in Sec. IV, and Sec. V contains concluding remarks.

Magnetic latch for disk drive actuator

Abstract: A limit stop/latching assembly in a disk storage system includes a crash stop for limiting travel of the actuator carriage at a fixed stop position. The assembly has a carriage latch incorporated with the crash stop. A magnetic latch actuator plate extends from the actuator carriage and is movable with the actuator carriage in a path of travel of the actuator carriage to abut the stop position. The carriage latch has a magnet and a pair of magnetic pole pieces abutting the magnet wherein the distance between the pole pieces defines a first gap and the distance between the pole pieces and the latch actuator plate defines a second gap. The latch is moved between a latched position, wherein said pole pieces are in magnetic contact with the latch plate, and a free position, wherein the actuator carriage is pivoted such that the second gap is greater than the first gap whereby magnetic flux is channeled substantially through the first gap to enable the latch plate to move remote from the crash stop.

Suspension control system

Abstract: In a suspension control system, accelerations detected by acceleration sensors are differentiated by a differentiator to calculate acceleration derivative values. Based on these values, a target electrical current calculating section calculates a target electrical current that is supplied to an actuator which controls a damping force of a damper. Before a rolling or pitch angle occurs in the vehicle, the change of the rolling or pitch angle is predicted to control the damping force of the damper, thereby improving the response of rolling angle and pitch angle control to achieve, simultaneously, an accurate posture control and a satisfactory riding comfort. Because the target electrical current calculating section corrects the target electrical current of the actuator based on a damper speed obtained by differentiating a damper displacement, even when a large input is applied to the damper due to an unevenness of the road surface, a proper posture control is performed.