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Control system for the movement of a pistonRelated Patent Categories: Pumps, ProcessesControl system for the movement of a piston description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060140777, Control system for the movement of a piston. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to fluid-pumping devices such as, for example, linear compressors and, particularly, to a system and a method for controlling this kind of device, being driven by a linear electric motor. DESCRIPTION OF THE PRIOR ART [0002] A linear motor is an ancient idea, but it was carried out only recently with maturation in the field of control and actuation of electric machines. A linear motor replaces rotary electric motors with many advantages, among which the economy of electric energy, since it used a more direct conversion of electric energy with less loss. Especially the use of linear compressors in present-day cooling cycles has been scarce due to the technologic difficulties usually encountered. [0003] The configurations of a linear motor and of a linear compressor may vary; the latter may be of simple or double effect, while the motor may comprise a work coil and a magnet; and this magnet may be either moveable or static. [0004] In the case of the linear compressor in question, one has opted for the simple effect, a fixed coil and a moveable magnet. [0005] Linear-type compressors are known from the prior art and are constituted by a mechanism in which the piston makes an oscillatory movement, and in most cases there is an elastic means interconnecting the cylinder and the piston, which imparts a resonant characteristic to this movement the energy being supplied by a linear-displacement motor. Equivalents such as piston-actuated water pumps or any fluid-pumping device can benefit from the object of the present invention. [0006] In any case, in order to prevent the piston from moving past the desired amplitude, which might cause damage to the valve plate, the movement of said piston should be controlled. [0007] A solution for controlling the movement of the piston is described In document U.S. Pat. No. 5,704,711, in which the piston stroke is primarily proportional to the voltage level imposed on the linear motor, which is of the fixed-magnet and moveable-coil type. In this solution the mechanism is constructed in such a way, that the ratio between piston stroke and piston diameter is great, which causes the variation of the end position reached by the piston during its oscillatory movement, due to the variations in feed voltage and load, not to interfere significantly with the characteristics of effectiveness and capacity of the compressor cooling. [0008] In this solution the mechanism is provided with a discharge valve constructed in such a way, that, if the piston exceeds the maximum displacement course expected in its oscillatory movement, for instance when the voltage imposed on the motor is excessive, there will be contact of the piston with this discharge valve, and this valve will allow the piston to advance a little, thus preventing an impact against the plate of the valve head. [0009] Another known solution is described in document U.S. Pat. No. 4,602,174, where the course of displacement of the piston is also primary proportional to the voltage imposed on the linear motor, which is of the moveable-magnet and fixed-coil type. [0010] In this solution the design of the mechanism does not allow the piston to advance past a determined point; otherwise, the piston would collide with the valve plate. Due to the search for a more optimized design, as far as efficiency is concerned, the ratio between the course of displacement of the piston and the diameter of the piston is not great, which makes the performance of the compressor more dependent upon the variations in the course of displacement of the piston. As an example, the gas-discharge process gives a very small option of the course, namely about 5% of the total. [0011] Another effect that occurs with this type of compressor is the displacement of the middle point of the oscillatory movement, whereby the piston is moved away from the discharge valve. This is because of the elastic deformation of the resonant mechanical system, formed by the piston and by a spring, when there is a difference in pressure between the two sides of the piston. This deviation from the middle point of the oscillatory movement is proportional to the difference in pressure between the discharge and the suction. [0012] For the above reasons, in this situation, it is necessary to control the course of displacement of the piston, by means of a device that controls the voltage imposed on the linear motor, re-fed by the information of piston position, basically estimated on the basis of the information about the current supplied to the motor and the voltage induced in the motor terminals. Solutions like this are described in documents U.S. Pat. No. 5,342,176, U.S. Pat. No. 5,496,153, U.S. Pat. No. 5,450,521, and U.S. Pat. No. 5,592,073. [0013] One of these solutions can be found In document EP 0 483 447 which discloses a system that controls the duty cycle In pulse with modulated voltage applied to electric motors. This system is configured to regulate the piston's movement to operate at constant amplitude, by generating a train of rectangular voltage waves which are in inverse proportionality to the supplied voltage. The avoidance of collisions of the piston in this solution is not effective. [0014] Another solution for controlling the movement of the piston is described in document PI 9907432-0. According to the solution described therein, a monitoring system is foreseen for monitoring the times the piston passes by a determined reference point within the compressor. In this way, when the residence time of said piston beyond the reference point exceeds a pre-established value, the voltage level is momentarily reduced during the respective movement, thus avoiding a collision with the valve plate. [0015] Further according to another technique described in document JP 11336661, the movement of the piston is controlled by counting discrete points thereof along the cylinder of the compressor. In case the piston moves excessively, the value of the average voltage applied to the respective motor is reduced so as to decrease the movement amplitude of said piston. [0016] Another way adopted to provide re-feeding to this voltage controller is to observe whether the piston collides with the valve plate. Such a collision is detected by means of a microphone or accelerometer, which generates a command for reducing the voltage applied to the motor and consequently the course of displacement of the piston. OBJECTIVES OF THE INVENTION [0017] The objective of the invention is to control stroke course of displacement of the piston of a linear compressor or of any fluid-pumping device, such as piston-actuated water pumps, allowing the piston to advance as far as the end of its mechanical course of displacement, even In extreme load conditions, without allowing the piston to collide with the valve system. [0018] It is also an objective of the present invention to control the course of displacement of the piston of a linear compressor or of any fluid-pumping device, allowing the piston to advance as far as the end of its mechanical course of displacement, even in extreme load conditions, without allowing the piston to collide with the valve system, even in the presence of external disturbances of the power-feeding network. [0019] Another objective of the present invention is to provide control over the course of displacement of the piston of a linear compressor or any other fluid-pumping device, without the need for information about the displacement of the middle point of oscillation of the piston. [0020] A further objective is to provide control over the amplitude of the course of oscillation of a linear compressor or any fluid-pumping device, allowing control over the cooling capacity developed by the compressor. [0021] Also other objectives of the present invention are to obtain a control system that meets the objectives of the present invention, that is easy to implement on an industrial scale and that has a low unit cost of manufacture and replacement, and to obtain a system that is self-fed, dispensing with the use of an additional external source, and that still has a low consumption of electric energy. BRIEF DESCRIPTION OF THE INVENTION Continue reading about Control system for the movement of a piston... Full patent description for Control system for the movement of a piston Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Control system for the movement of a piston patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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