ELECTRONIC PUMP CONTROL

Abstract: There is disclosed an electronic control means for a pump, the control means comprising: input means, for accepting input signals, the input signals being indicative of the values of variable quantities which determine a desired flow rate of a fluid which, in use, is to be supplied by a pump; an electronic memory, comprising a plurality of memory locations, each memory location corresponding to a particular combination of values of the variable quantities and containing a stored control signal corresponding to the desired fluid flow rate determined by those values; and output means, for supplying the control signal, in use, to the pump. More specifically, there is diclosed equipment suitable for distributing a fluid over an area of land, the equipment comprising distribution means, to which fluid is supplied by a pump driven by an electric motor, the delivery rate of the fluid from the pump being a function of the operating speed of the pump, the equipment further comprising such control means.

Description: This invention relates to an electronic control means, which is particularly intended to be used to control the operation of a pump. In common use is a small electric pump, operated by a D.C. motor, the operation of the motor, and hence the flow rate of fluid supplied by the pump, being controlled by a voltage applied to the pump. In many circumstances, for example when applying a potent and expensive weedkiller to an area of land, it is important to deliver a quantity of fluid which can be accurately measured and controlled. In such circumstances, it is important to be able to supply to the pump an input signal which may be varied with the particular operating conditions, but which may be accurately maintained once set. EP-A-0155850 discloses a weedkiller delivery unit including input means, for accepting signals indicative of the values of the desired area concentration of the weedkiller and the desired travel speed of the unit, and means for supplying to a pump an output signal to control the output thereof. Moreover, in other known weedkiller delivery units, the delivery device itself is a hand-held piece of equipment, used by an operator walking across the area to which the weedkiller is to be applied. In these circumstances, it is advantageous if any control means for the pump additionally forms part of the hand-held equipment, in which case it must be made small, light and robust. According to a first aspect of the present invention, there is provided fluid distribution equipment comprising a pump driven by an electric motor, the equipment further comprising electronic control means for the pump, the control means comprising: input means for accepting input signals, the input signals being indicative of the values of parameters which determine a desired flow rate of a fluid which, in use, is to be supplied by the pump; and output means for supplying a control signal, in use, to the pump, characterised in that the control means further comprises an electronic memory comprising a plurality of memory locations, each memory location corresponding to a particular combination of values of the parameters and having stored thereat the control signal to be supplied to the pump, corresponding to the desired fluid flow rate determined by those values; and in that a first of said parameters is a scale factor. In preferred embodiments of the invention, the parameters, values of which may be input by an operator, and which determine the desired fluid flow rate, are the width of a strip of land which is to be sprayed, the volume of fluid which is to be applied to a unit area of that land, and the linear speed of the operator along the strip. Preferably, the input value of the scale factor may be selected in dependence on the value of a calibration test. Preferably, at least one first value of the scale factor corresponds to a first fluid which may be used and at least one second value of the scale factor corresponds to a second fluid which may be used. According to a second aspect of the present invention, there is provided a method of controlling the operation of a pump driven by an electric motor having electronic control means, the method comprising the steps of: supplying a plurality of input signals to the electronic control means, the input signals being indicative of the values of parameters which determine a desired flow rate of a fluid which is to be supplied by the pump, and a first of said parameters being a scale factor; retrieving from an electronic memory, at a location defined by the values of the input signals, a stored control signal corresponding to the desired fluid flow rate determined by those values; and supplying the control signal to the pump. For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a block diagram illustrating the known control system associated with a conventional pump; Fig. 2 is a plot of the pump speed/flow rate characteristic of a known pump; Fig. 3 shows, schematically, an electronic control means in accordance with an embodiment of the invention; Fig. 4 shows, in more detail, the circuitry of the embodiment illustrated in Figure 3; Fig. 5 illustrates the type of equipment which may be provided with control means according to the present invention; Fig. 6 is an enlarged perspective view of the handle of the equipment shown in Fig. 5; and Fig. 7 is a different perspective view of the handle shown in Fig. 6. Figure 1 illustrates the control system which is associated with conventional pumps. A pump control 1 acts upon an input voltage V IN to cause a pump 2 to rotate at a speed proportional to the applied voltage. Figure 2 illustrates the characteristic of the system. Thus, increasing the speed of rotation of the motor in the pump 2 produces, generally, an increase in the rate of flow of fluid supplied by the pump, although this relationship is non-linear. The range of flow rates which it will be necessary to supply will be known, and the desired flow rate for any particular set of operating circumstances may be calculated. For example, if the pump is to supply fluid which is to be applied to an area of land, the flow rate required is equal to the product (in appropriate units) of the volume of fluid to be applied to a unit area of land, the width of a strip to which fluid is to be applied, and the linear speed of the spraying apparatus along the strip. Once the desired flow rate is known, then so, from Fig. 2, is the required pump speed. The present invention is concerned with manipulating inputs corresponding to the variables which determine the desired flow rate and generating an output signal which, applied to the known pump, will produce the appropriate flow rate. Figure 3 shows an embodiment of the invention, in which the inputs comprise four digital signals. In the embodiment illustrated, the inputs 21, 22, 23, 24 are each capable of accepting either a 3 or 4 bit digital input signal. For example, in a preferred embodiment of the invention, three input variables are, as described above, the volume of fluid per unit area of land, the width of a strip of land to be sprayed, and the linear speed of the sprayer. The width may be chosen to be any one of eleven available values, and so a 4 bit input is allocated to this variable. The other two flow rate determining input variables may each take any one of eight available values, and thus to each of these variables is allocated a 3 bit input. Each available value of the inputs might be allocated to an integer or non-integer value (in appropriate units, such as litres per hectare, metres, or miles per hour) of the variable, as is necessary to give the required accuracy. However, using the example given above and allocating an integer value of the respective unit to each available input signal, if the width to be sprayed is 1 metre, this might be input at input means 22 as the binary signal 0001. Similarly, a speed of 2 mph (0.89 m/s) might be input at input means 21 as the binary signal 010, and a volume of 5 litres per hectare might be input at input means 23 as binary signal 101. The fourth input 24 is provided to allow scaling of the output signal. The flow characteristics of the pump will depend upon the properties of the fluid being used and may also vary with time as a result of wear. Thus, before using the device, a flow test may be carried out, with the actual flow rate achieved for a given set of input parameters being compared with a nominal flow rate. The actual flow rate might vary, for example, from 65% to 135% of the nominal rate, and this percentage may be used to determine which of the available scaling factors is input at 24. In other circumstances, it may be appropriate to use a different set of variables, and such a different set may include more or less than four variables. For example, the electronic control system may be used in conjunction with spray equipment which is designed to be operated at a constant speed, and which incorporates means for ensuring that the speed is held constant. In such a situation, it would not be necessary to include a means for inputting a value for the speed, as appropriate compensation for this could be incorporated in the control system 1 of the pump. Similarly, the electronic control system would need to accommodate more than three input flow rate determining variables if the system was designed such that, for example, the operator walking holding the device was required to input not a linear speed but a pace length and a time taken for each pace. The inputs from the input means are combined in line 27, to form a 14 bit digital address. This address corresponds to a particular location in a memory 28, which may be ROM, PROM, or EPROM. Stored at this location may be a digital signal corresponding to the desired pump speed required for the particular values of width, speed, volume and the scale factor uniquely specified by this address. If the memory 28 is 8 bits wide, then 256 output signals are available. Alternatively, the selected combination of input variables may be such that the required pump speed is higher than the maximum speed of the pump or lower than the minimum speed at which the pump operates reliably. In that case, a suitable warning signal may be provided. In effect, the provision of the scale input 24 allows up to sixteen different flow curves to be stored, and the selected input may be the one, for which the flow curve corresponds most closely to the actual characteristic of the pump at that time, and using the required fluid. The digital signal stored at the selected address in the memory 28 is passed along a line 29 to electronic switching circuitry 30, the output of which is fed to a pulse width modulator 31. The pulse width modulator 31 provides output pulses, the mark-space ratio of the output signal depending upon the signal fed from the electronic switching circuitry 30 to the pulse width modulator 31. In the preferred embodiment of the invention, the pulse width modulator 31 provides a series of pulses, each of duration 18ms, although this pulse width may be varied if desired, and the time between pulses varies from 0 to 0.75s. This signal, in which each pulse is of 8.0V, is then fed to the pump motor. The reason for providing a pulse width modulated signal in this way, rather than, for example, altering the magnitude of a voltage fed to the pump motor, is to allow the use of a relatively small motor, which would be unable to provide sufficient output torque at low input voltages. The pulsed signal provided by the pulse width modulator 31 causes the motor to step, rotating for a short distance at a time. However, the time taken for fluid to flow along most flow lines ensures that this stepping does not prevent an even flow of fluid at the delivery head. In Figure 5, the circuit embodiment shown in Figure 4 is illustrated in more detail. In particular, it can be seen that the switching circuitry 30 comprises a pair of switching ICs 32a, 32b, which determine which resistors in a resistor ladder 33 are short-circuited, and hence determine the size of the output signals fed to the pulse width modulator circuitry 31. The inputs may be supplied to the input means by rotating dials, or, with suitable modifications to the circuitry shown in Figure 5, by using a suitably connected keypad. In a further modification, one or more of the digital inputs may be determined, not directly the operator, but by sensors associated with the equipment. For example, the speed of movement of a towed system could be digitised and used instead of an input set by the operator. Similarly, if the electronic control means is to be used in conjunction with a known device in which the width of the strip which is to be sprayed is determined by the speed of rotation of discs in the head of the spraying equipment, the "width" input may be obtained, not directly from the operator, but from the voltage control means by which the operator controls the speed of rotation of those discs. Figs. 5 to 7 illustrate spraying equipment, with which the control circuitry of the present invention may be used. The equipment comprises a lance 100, having a handle 101, a fluid passage 102, and a head 103. Thus this equipment is designed to be carried by a pedestrian. Fluid is supplied along an inlet pipe 104, and then along the fluid passage 102 to the head 103. Located in the head 103 are rotating discs, which create droplets of the fluid, for example a herbicide, which are then dispersed. The fluid delivery rate is controlled by a pump, powered by an electric motor, and is designed to be carried separately by the pedestrian operator, for example as a backpack. Electrical connection between the control circuitry and the electric motor is provided by a lead 105. To prevent possibly dangerous fluids being inadvertently sprayed, the handle is designed such that fluid is allowed to flow along the passage 102 only when a gripping element 106 is squeezed against the body of the handle 101. Located on the handle 101 are an on-off switch 107 and a rotary switch 108, for controlling the speed of rotation of the discs located in the head 103. Also located on the handle 101 are four further control knobs 109a, 109b, 109c, 109d, which may be rotated to input, into the control circuitry according to the present invention, the appropriate values of the variable quantities which are being used to determine the required fluid delivery rate. The handle may be provided with a power source for the control circuitry or the spinning discs, such as one or more rechargeable battery. Thus, the handle is further provided with a socket 110, allowing recharging to take place when the equipment is not in use. Thus, embodiments of the present invention provide electronic control means which, while of simple design and easily portable, can accurately control the rate of application of a fluid.

Claims: Fluid distribution equipment comprising a pump driven by an electric motor, the equipment further comprising electronic control means for the pump, the control means comprising: input means (21,22,23,24), for accepting input signals, the input signals being indicative of the values of parameters which determine a desired flow rate of a fluid which, in use, is to be supplied by the pump; and output means (30,31), for supplying a control signal, in use, to the pump, characterised in that the control means further comprises an electronic memory (28), comprising a plurality of memory locations, each memory location corresponding to a particular combination of values of the parameters and having stored thereat the control signal to be supplied to the pump, corresponding to the desired fluid flow rate determined by those values; and in that a first of said parameters is a scale factor. Fluid distribution equipment as claimed in claim 1, wherein the input value of the scale factor may be selected in dependence on the result of a calibration test. Fluid distribution equipment as claimed in claim 1 or 2, and wherein at least one first value of the scale factor corresponds to a first fluid which may be used and at least one second value of the scale factor corresponds to a second fluid which may be used. Fluid distribution equipment as claimed in claim 1, 2 or 3 further comprising distribution means, to which fluid is supplied by the pump, the delivery rate of the fluid from the pump being a function of the operating speed of the pump; wherein the distribution means includes means for determining the width of a strip of land over which fluid is distributed, and wherein a second of said parameters is the width of the strip of land over which fluid is to be distributed, the input signal which is indicative thereof being used to control the distribution means. Fluid distribution equipment as claimed in any preceding claim, wherein the parameters include the volume of fluid which is to be applied to an area of land or the linear speed of the equipment over the land. A method of controlling the operation of a pump driven by an electric motor having electronic control means, the method comprising the steps of: supplying a plurality of input signals to the electronic control means, the input signals being indicative of the values of parameters which determine a desired flow rate of a fluid which is to be supplied by the pump, and a first of said parameters being a scale factor; retrieving from an electronic memory, at a location defined by the values of the input signals, a stored control signal corresponding to the desired fluid flow rate determined by those values; and supplying the control signal to the pump. A method as claimed in claim 6, comprising the further steps of: carrying out a calibration test, to compare the fluid flow rate which is achieved with the desired fluid flow rate; and adjusting the value of the scale factor to adjust the fluid flow rate. A method as claimed in claim 6 or 7, wherein at least one first value of the scale factor corresponds to a first fluid which may be used, and at least one second value of the scale factor corresponds to a second fluid which may be used. A method as claimed in claim 6, 7 or 8, wherein the parameters include some or all of: the volume of fluid which is to be applied to an area of land, the linear speed of the equipment over the land, and the width of a strip of land over which fluid is to be distributed.

Inventors: GILL, DAVID CHARLES
Applicants: NOMIX-CHIPMAN LIMITED
Application year: 1988
Main classification: G05D7
IPC codes: B05B9, B05B12, G05D7, A01M7