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Method for controlling a pump meansRelated Patent Categories: Pumps, ProcessesMethod for controlling a pump means description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070014673, Method for controlling a pump means. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a method for controlling a diaphragm or piston pump that is actuated via a ram or a connecting rod by a cam which is powered by an electric motor. [0002] Diaphragm and piston pumps are used to supply metered quantities of liquids with various properties. Depending on the field of application, the pump behaviour is subject to various requirements in order to ensure that the delivered quantity of metered medium is as precise as possible and remains constant for as long as possible. [0003] The pumps are driven by an electric motor via a cam, in such manner that the rotational motion of the motor is converted to linear motion of the pump diaphragm or pump piston. For each rotation of the cam, a compression stroke takes place, with delivery of the metered medium for example into a metered line, and an aspiration stroke, in which the metered medium is aspirated from a reservoir or similar. [0004] Electric motors used in the prior art for driving such mechanisms include a wide range of types, particularly mechanically commuted motors, synchronous and asynchronous motors and stepping motors. However, most such drive units are, associated with a number of disadvantages with regard to their respective use. [0005] Mechanically commuted motors are prone to a high rate of mechanical wear and are therefore unsuitable for pumps with very long lifetimes. [0006] The torque gradient of synchronous motors is disadvantageous in that it causes the frictional connection to be broken if placed under excessive load. The startup behaviour is also not ideal for the present purpose. Asynchronous motors have a rotating speed curve that is dependent on its load, which is detrimental for precise metering of quantities. The rotating speed of both synchronous and asynchronous motors is dependent on the frequency of the applied voltage, which means that electronic frequency converters are needed to control the rotating speed. [0007] Particular problems arise when the pump is to be operated at less than its maximum metering output, which is unavoidable in many applications for precisely metered delivery. A variety of methods have been implemented to combat this in the prior art. Thus the delivered quantity of metered medium may be reduced by limiting the excursion of the pump diaphragm or piston. In this case, the cam runs freely for a part of its revolution and only moves the diaphragm or piston in a more or less extended area about front dead centre. The particular drawback of this method is that the piston or diaphragm is accelerated very rapidly for short periods depending on the delivery power, which leads to high pressure variations in the metered lines and negatively affects the metering behaviour. In the same way, the aspiration behaviour is impaired during the aspiration stroke, which degrades the aspiration behaviour of the pump if there is any air trapped in the suction line or in the case of small pump heads. [0008] A further variant for reducing the delivery volume is pulse-pause control. In this, a metering cycle is completed and is then followed by a metering pause, which is dependent on the desired delivery quantity, and is calculated so that the desired delivery quantity is adjusted in the temporal average. The disadvantage of this arrangement is that the pauses occurring for low delivery quantities are very long, which can cause unacceptable mixing of the metering medium in the pipeline or the tank, and is moreover associated with highly inconsistent delivery behaviour. [0009] A further option for reducing the metered quantity is to control the rotating speed of the drive motor. In this case, the delivery quantity may be adjusted by influencing the speed of the piston or diaphragm. A corresponding slowing of the drive unit and thus of the diaphragm causes a reduction in the quantity of metered medium delivered per unit of time. The problem with this approach is that under certain circumstances for a desired lengthening of the compression stroke the aspiration stroke is also lengthened at the same time. The suction and delivery behaviour is degraded thereby, particularly when dealing with highly viscous media. [0010] In order to avoid this problem, the applicant's DE 198 23 156 A1 describes a method for operating a metering pump with an asynchronous motor. In this case, the rotating speed of the asynchronous motor is reduced during the compression stroke according to the desired metered output. During the aspiration stroke, on the other hand, the rotating speed is increased to achieve the shortest possible aspiration stroke, and thereby also shortening the pauses between compression strokes. The disadvantage of this method is that the use of an asynchronous motor necessitates a highly sophisticated system configuration, which requires a frequency converter to control the rotating speed of the asynchronous motor and sensor equipment to monitor and control the rotating speed of the motor in order to be able to compensate for the deviation caused by the load-dependent rotating speed curve. [0011] Accordingly, the task of the present invention is to provide a method for controlling a diaphragm or piston pump that is actuated via a ram or a connecting rod by a cam which is powered by an electric motor, which allows the most precise and constant delivery possible of metered media, combined with a simple construction. [0012] This task is solved with a method according to the type described in the introduction in which the diaphragm or piston of the pump is moved by the drive unit of the cam at approximately constant speed throughout the compression stroke, taking into account the position of the cam, to assure an approximately constant volume flow of the metered medium. [0013] The diaphragm or piston mechanism, driven by a circular cam which is rotating at constant speed, now describes a sinusoidal speed profile. Starting from the rear dead centre, the diaphragm is accelerated, reaches the fastest speed of the compression stroke after a quarter revolution, and then slows down again until front dead centre of the cam, at which point it then transitions to the aspiration stroke, which also includes a period in which the diaphragm speeds up to its maximum speed halfway through the aspiration stroke, and is then slowed until the cam reaches rear dead centre. [0014] In the method according to the invention, the speed of the cam is now controlled during the compression stroke in such manner that the speed profile produced is as linear and constant as possible, instead of the non-linear, sinusoidal profile created without the control. To produce this, the cam must be accelerated sharply at the start of the compression stroke and must be slowed to a minimum value by the middle of the compression stroke, at which point it is accelerated again to reach maximum speed again close to the front dead centre. This form of control of the cam speed results in a speed profile of the diaphragm or piston that is highly linear and essentially at a constant level. [0015] This approximately constant diaphragm speed during the compression stroke causes the metered medium to be delivered at a uniform rate, which leads to highly advantageous and precise metering behaviour, even for very viscous media. A good delivery result may also be achieved by this means for very small metering outputs. [0016] Refinements of the invention are described in the subordinate claims. Accordingly, one refinement of the invention is characterised in that the drive unit drives the cam during the compression stroke with a rotating speed profile that compensates for temporal cosinusoidal movement of the piston or diaphragm conditioned by the cam. [0017] Moreover, it may also be provided that the speed profile of the drive unit has approximately the shape .omega.(t)=2/T.sub.D.times.(1-(-2/T.sub.D.times.t+1).sup.2).sup.-1/2 in the compression stroke throughout the period of constant diaphragm speed. [0018] The physically correct formula indicated above for compensating the cosinusoidal piston or diaphragm movement is derived by transformation of the linear movement via an arc cos function and subsequent differentiation. A similar equation is derived for drive units with additional transverse movement (connecting rods). [0019] For practical cosine compensation, the above formula may be approximated with a simplified or similar formula depending on an acceptable non-linearity of the metered quantity. [0020] The angular velocity of the cam shown results in a constant speed of the diaphragm, except at the start and end of the compression stroke. TD represents the length of the compression stroke, the maximum diaphragm excursion being standardised to 1. [0021] It is also possible that the drive unit moves the cam with a different speed profile, particularly with constant and/or higher speed, during the aspiration stroke. [0022] It is desirable to keep the aspiration stroke as short as possible. In this case, depending on the metered medium it is not absolutely essential to achieve constant pressure distribution during the aspiration stroke. As a result, at the end of the compression stroke, when the rotating speed of the cam is at its greatest, as previously described, delivery can be continued at this speed, which leads to a short aspiration stroke with sinusoidal diaphragm speed. The next compression stroke can then be begun at this increased speed, which ultimately provides good system response and is less harsh on the mechanical parts of the pump. [0023] On the other hand, maintaining the pressure distribution as constant as possible during the aspiration stroke as well may be desirable, particularly for more viscous metered media, so that a rotating speed profile similar to that of the compression stroke is selected rather than constant rotation, when it may be necessary to set a higher diaphragm speed and thus a shorter period for the aspiration stroke. [0024] It is advantageous if the delivered volume flow of metered medium is increased shortly before the end of the compression stroke in order to compensate for the metering gap during the aspiration stroke. Continue reading about Method for controlling a pump means... Full patent description for Method for controlling a pump means Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for controlling a pump means 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. Start now! - Receive info on patent apps like Method for controlling a pump means or other areas of interest. ### Previous Patent Application: Digital incremental flow analysis system Next Patent Application: Variable displacement compressor Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Method for controlling a pump means patent info. 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