Pumps – Condition responsive control of pump drive motor – By control of electric or magnetic drive motor
Reexamination Certificate
2001-01-03
2002-10-01
Tyler, Cheryl J. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
By control of electric or magnetic drive motor
C417S045000, C417S063000, C417S053000
Reexamination Certificate
active
06457944
ABSTRACT:
BACKGROUND
1.0 Field of the Invention
The invention relates to a method of operating a dosing pump, which is driven by an asynchronous motor, with a pump drive, which converts the motor revolutions into pump strokes consisting of a pump suction cycle and pump pressure cycle and having a defined stroke frequency, wherein continuous pump strokes are carried out during a dosing phase.
2.0 Discussion of the Related Art
Various forms of dosing pumps driven by an electric motor are used for dosing liquids of the most diverse kinds in precise quantities. From a motor power of about 40 watts, the preferred use for such dosing pumps is asynchronous motors supplied by a 230 volt or 115 volt standard operating mains with alternating voltage and alternating current at a mains frequency of 50 or 60 hertz. As long as a mains voltage of 230 volts and the mains frequency of 50 or 60 hertz are applied to the asynchronous motor of these dosing pumps, the asynchronous motors run at a load-dependent, almost constant rotational speed. The motor rotational speed is converted by way of a transmission arrangement into pump strokes performed by a pump element, for example a piston or a diaphragm, producing the respective pump suction and pressure cycles. In the case of a dosing pump driven by an asynchronous motor with 230 volts and 50 or 60 hertz, the maximum stroke frequency, which is predetermined by virtue of the transmission arrangement, is usually between 120 and 180 strokes per minute. Each stroke consists of one suction cycle and one pressure cycle of the pump. Electrical drive control signals, which allow the asynchronous motor to execute a respective stroke of the pump element, for example diaphragm or piston, are supplied to the asynchronous motor by a so-termed water meter or a standard signal transmitter or an internal cycle transmitter. The drive control signals are repeated until the number of strokes carried out for the desired dosing quantity has been performed. A dosing phase of the pump is composed of this number of strokes. A dosing phase is triggered by an electrical start signal supplied to the dosing pump.
In these pumps an alternating voltage with constant frequency is applied during each stroke consisting of a suction cycle and pressure cycle, so that the suction cycle and pressure cycle demand the same period of time. This has the consequence that the product in the dosing duct connected to the pump is conveyed for the time corresponding to the respective pressure cycle, and a standstill phase or “dosing gap” subsequently arises in the dosing duct for the same length of time of the suction cycle before further product is conveyed in the dosing duct by a new pressure cycle. This can lead to an unsatisfactory conveying of product in the dosing duct.
This problem is even more serious in cases where the pump is to dose at a stroke frequency lower than the maximum possible frequency. This occurs when by the asynchronous motor is initially being switched on by means of a drive control signal for a complete stroke consisting of a suction cycle and pressure cycle, but subsequently remains switched off for the duration of a time period necessary for achieving the desired stroke frequency before a new stroke is started by a new drive control signal. An even more unfavourable distribution of the product, which is to be dosed, in the dosing duct results from this so-termed pulse/pause drive control, and so-termed dosing clouds arise at intervals of greater or lesser length.
Another possibility of reducing the stroke frequency consists controlling the asynchronous motor in drive by way of a frequency changer, which supplies to the motor an alternating voltage frequency or alternating current frequency lowered by comparison with the mains frequency of 50 or 60 Hertz. This has the consequence that the motor rotational speed and thus the stroke frequency of the pump are reduced. With the lowered frequency, the time duration of the suction cycle and pressure cycle and thus the stroke frequency are prolonged due to the lower motor rotational speed. The suction cycle and pressure cycle are, however, still of equal length, which means of the same duration in time. The advantage relative to the first method is that due to the prolonged cycle times a pause drive control during which the motor is stopped is no longer necessary for achieving the desired stroke frequency. The pressure cycle is prolonged relative to a pulse/pause drive control at the same stroke frequency, so that a better distribution of the product, which is to be dosed, in the dosing duct is established. However, the suction cycle is also drawn out to the same degree, as a result of which the problem of large gaps without product, which is to be dosed, in the dosing duct still arises.
With the problems of the prior art in mind, an object of the invention is to improve; and dosing performance during operation of dosing pumps with an asynchronous motor drive.
In one embodiment of the invention, this object is met by application, in each pump stroke, to the asynchronous motor of an electrical alternating voltage at higher frequency during the pump suction cycle, and the same electrical alternating voltage at lower frequency relative to that in the pump suction cycle during the pump pressure cycle. The possibility is thus created by the invention of structuring the length or duration in time of the suction cycle and pressure cycle of a stroke to be different. The higher the frequency applied to the asynchronous motor during the suction cycle, the faster the motor turns and the shorter the suction cycle. On the other hand, the lower the frequency, the longer the pressure cycle. It is thus possible to significantly shorten the suction cycle relative to the pressure cycle in its length or duration in time. If a shortest possible suction cycle and a longest possible pressure cycle are desired, the disadvantageous “dosing gaps” in the state of the art no longer arise. The length of the suction cycle is minimized, and thus the time during which no product in a dosing duct is dosed is kept as short as possible, by application of the higher frequency during the suction cycle. The suction cycle is then adjoined by the pressure cycle. This can be regulated in its duration or length in terms of time by application of an appropriate lower alternating voltage frequency to the asynchronous motor, so that a time duration for each stroke consisting of a suction cycle and pressure cycle results, which duration corresponds to the desired stroke frequency. The pressure cycle is, through application of the lower frequency, arranged to be as long in time as possible having regard to the predetermined stroke frequency, i.e. it is maximized in terms of time.
Thus an almost constant dosing of the product in a dosing duct is possible by the invention, with interruption merely by short gaps during the suction cycle. In addition, a further advantage by comparison with pulse/pause control is that due to the regulable frequency during the pressure cycle, the length or duration thereof in time can be set, in particular, independently of the suction cycle and thus the desired stroke frequency can be achieved. As pause times no longer arise during which the asynchronous motor is stopped, the pump drive is mechanically treated in a more gentle manner. By contrast to pulse/pause control it is no longer exposed to any shock loadings, whereby the service life of the drive is increased, particularly in the case of a higher pump output.
The invention thus generally provide that the pump suction cycle and pump pressure cycle are regulated in a different manner with respect to their duration or length in time whereby they are controllably different. This contrasts with the state of the art, in which the suction cycle and pressure cycle are arranged to be of equal length.
It is advantageous if a frequency (typically 50 Hertz or 60 Hertz in the US), above the frequency of a usual 230 or 115 volt standard operating mains is applied as the higher frequency and a frequency below
Haberlander Albert
Hunklinger Herbert
Gray Michael K.
Lang Apparatebau GmbH (Lang)
Merchant & Gould P.C.
Tyler Cheryl J.
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