Linear actuator

Résumé

A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and dampers, and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion. Many other mechanisms are used to generate linear motion from a rotating motor. Types Mechanical actuators Mechanical linear actuators typically operate by conversion of rotary motion into linear motion. Conversion is commonly made via a few simple types of mechanism:

Screw: leadscrew, screw jack, ball screw and roller screw actuators all operate on the principle of the simple machine known as the screw. By rotating the actuator's nut, the screw shaft moves in a line.
Wheel and axle: Hoist, winch, rack and pinion, chain drive, belt drive, rigi

Source officielle

https://en.wikipedia.org/wiki/Linear_actuator

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Control of velocity for a linear actuator

Silas Kull

This project was done in the laboratory of integrated actuators (LAI) during the first master semester. It is part of a PhD-work with linear actuators, also called relays, where these actuators are optimized in design and equipped with a speed control during closure and aperture. The aim of this semester project was to find an optimal control algorithm for the closure of a relay. The relay has to follow a specific speed profile in function of position, so that a certain speed can be guaranteed near the contact closure position. To follow this speed profile, which has been developed by the corresponding company, will decrease electrical and mechanical wearout during closure. In this report, different approaches of control are shown and compared. It is also a report that should help as a guide to develop an optimal control for a specific relay. A final conclusion will give some advices on how to design an optimal control.

2010

Chargement

Nowadays many consumer electronic devices are using small engines (micromotors). Thanks to technological innovation, the components can be imbedded into numerous portable systems. The key factors for a nomadic integration are: reduction of power consumption, reliability, durability and manufacturing cost. From the perspective of an always denser integration, conventional fabrication techniques of motors are reaching their limits (windings, size of the permanent magnet). The technologies developed for the micro-electronics (thin film processes) offer new possibilities to create microscopic size motors. The potential for innovation in this field being very wide, many new concepts are based on this technology. Lots of research centers are trying to find new principles of actuation to increase the overall efficiency of motors. With the challenge of replacing a small "classical" motor by a micromotor based on thin film technologies, the electrostatic actuation is going to have a great potential in the future. Many problems are related to the compatibility of both technologies in terms of coexistence. This is mainly due to problems of dimensions and associated tolerances. The challenge of this research was to propose a solution for the creation of a micromotor including the following concepts: usable mechanical interface between an outer gear and the mechanical output torque of the micromotor (about 0:5 µNm), moderate energy consumption, relatively small chip size in relation to the required performances and finally ability to be easily implemented in a mechanism (module). This thesis presents the different aspects of the concept, design, simulation, fabrication and characterization of a MEMS based motor using silicon micro-technologies. The micromotor is constituted of a fixed base (stator) with an electrostatic actuator (force generator), a rotor and a protective cover (encapsulation). The principle of the electrostatic actuation is based on a comb inter-digitized configuration. A first interface (ratchet system) was developed to allow for the conversion of the back and forth movement of the linear type actuator to a circular motion of the silicon rotor. A challenge was to create an actuator able to deliver an electrostatic force of 500 µN with a applied potential of 40 V. To obtain this force, the actuator itself has an active area of over 10 mm2. The first concept has two large actuators representing 60% of the total area of the stator. In the second concept, the occupied area of the three actuators represents 40 % of the total area of the stator. Two systems were created during this work, based on the same principles of actuation and of actuator/rotor interfacing. The first system uses a crank mechanism to interface the silicon rotor and a metallic pinion. The encapsulation was achieved via a metal support on which a plastic lid was fastened. These two pieces were fabricated by conventional machining (milling) techniques. The micromotor module was made by assembling the different components. The second system was made based on a direct interface type (direct link between internal teeth of the silicon rotor and outer teeth of a metallic gear). The encapsulation concept uses only micro-technologies. The cover was made of a glass substrate on which a silicon spacer was bonded (anodic bonding process). The motor module was then achieved by assembling a silicon base (stator), a silicon rotor and a silicon/glass cover. In accordance with the specifications, the obtained results are very promising. The electrostatic force generated by the actuator is in the order of few hundreds of micronewton. The power consumption is in the order of few microwatts. Many innovative concepts have been studied and manufactured. Some of those have been patented, showing the interest of these new ideas. Experiments have demonstrated the functionality of a MEMS engine.

EPFL2010

Chargement

Design, Optimization, and Sensorless Control of a Linear Actuator

Joël Maridor

Electrical contactors are relays for interputing high currents (up to 2000 A). They consist of three main distinct parts: the low voltage circuit, the high voltage circuit and the linear actuator that moves the contact. The purpose of this thesis is to design, optimize and control the moving part of a linear actuator without external sensor. Indeed, it is very important to control the closing speed of the actuator in order to minimize the contacts wear. The speed should not be too fast so as not to damage the silver contacts at the impact and not too slow to avoid multiple arcs, which erode the contacts. The thesis is divided into different themes: the sensorless position detection, the optimization of the actuator, the signal processing of the position and the speed by adapting the Kalman filter, and finally the sensorless speed control of the actuator's moving part. Industrial constraints impose, for reasons of cost, a position detection without sensor. To do this, a high frequency signal (1250 Hz), named scan current, is superimposed to the one that drives the actuator's moving part. Then, the total current is filtered to obtain only the scan current. Its amplitude depends on the position because the inductance of the actuator windind varies greatly with the value of the airgap. It is therefore possible to detect the position using only the provided low voltage circuit. The optimization of the actuator is made by combining genetic algorithms and finite element modeling (FEM). The first objective to be achieved by the optimizer is to minimize the material cost of the actuator. Then, knowing the minimum price of the actuator, the cost becomes a constraint when optimizing for the best position detection. The optimal configuration presented in the thesis promotes the variation of inductance versus the position and thus allows the best position detection following the constraints defined by the specifications. The speed of the moving part is the derivative of the position but as this signal is noisy, the resulting speed is not exploitable as it is. Because the memory of the microcontroller is limited, an adapted Kalman filter method, simple and appropriate, is developed to allow filtering of the position and speed. Finally, the study of the speed control is first simulated using Matlab-Simulink in order to test different control strategies in both open and closed loops. They are then verified on the test bench with the industrial contactor and the optimized one. The results allow the validation of the different levels of the method of design, optimization and sensorless control of a linear actuator.

EPFL2011

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Design, Optimization, and Sensorless Control of a Linear Actuator

Joël Maridor

EPFL2011

EPFL2010