DC-Motor control circuit for a diaphragm pump

Abstract: A control device for a DC motor driving a diaphragm pump includes a pulse generating integral circuit and a variable voltage setting integral circuit. The variable voltage setting integral circuit sets a pulse-base voltage at such a level that the DC motor is not rotated, thereby a overshoot high voltage generating at rising and falling point of pulse is restricted. Discharge of the diaphragm pump is accurately regulated by means of modifying frequency, voltage, duty ratio of a pulse.

Description: Field of the Invention The present invention relates to a control device for a DC motor with a brush commutator for driving a crankshaft of a diaphragm pump, and particularly for controlling discharge of a DC motor driven diaphragm pump which is used as a metering injection pump. Background of the Invention EP-A-0 363 672 discloses that in a blood pressure monitor a blood pressure cuff is inflated by a pump driven by an electric motor. A control circuit calculates the rate of inflation of said cuff over a predetermined period, compares said rate to a desired rate and generates a control signal to adjust the current supply of said motor to control the inflation rate. The motor speed is controlled by the adjustment of the duty cycle of the voltage applied to said motor. US-A-4 547 680 discloses a diaphragm pump wherein the diaphragm is deformable by the reciprocable armature of an electromagnet which is energizable at a selected frequency by a timer circuit and at random frequency by a pulse generator. The pulse generator is connectable with the electromagnet by a cable having separable male and female coupling elements which automatically deactivate the timer circuit when the male coupling element is inserted into the female coupling element. A selector switch is provided to deactivate the timer circuit independently of the coupling elements. A knob serves to adjust a potentiometer of the timer circuit simultaneously with closing of the selector switch so that the frequency at which the timer circuit can energize the electromagnet is reduced to a minimum value. US-A-4,397,610 discloses a reciprocable liquid pump driven by a direct current electric motor wherein the motor drive voltage, and thereby pump reciprocation, and output pressure, is selectively controlled by a circuit including an electromechanical transducer coupled in pressure sensing relation to the liquid pump output, a manually operable pressure set point switch, and a silicon-controlled rectifier circuit. The document is directed to improvements in pressure regulation and control for pumping systems, preferably pumping systems adapted for portable paint spraying equipment, wherein the pressure fluctuation range may be reduced by at least an order of magnitude from prior art systems. The apparatus includes a direct current (DC) motor mechanically coupled in driving relationship to a reciprocable pump, wherein the pump output pressure is monitored by an electromechanical sensing device which delivers a voltage signal proportional to pump output pressure. The voltage signal is connected to an electronic circuit which has as another input a manual voltage setting for adjusting a setpoint pressure, the setpoint signal and pressure signal being compared and the difference between the two signals generating an error drive signal which is amplified and compared against a DC voltage reference and a timing signal. The combination of the timing signal and the error drive signal is used to develop a gating signal over a portion of the timing signal period. The gating signal is fed into a silicon controlled rectifier (SCR) circuit for controlling the gating time of the silicon controlled rectifier circuit so as to regulate the DC drive voltage into the motor. When the set point and pressure signals become equal the SCR voltage drive into the motor drops to near zero, but motor drive current remains at the level necessary to develop sufficient motor torque to hold the pump output pressure at the set point value. Under other set point and pressure signal conditions a DC drive signal is coupled into the motor to provide a DC drive voltage of sufficient magnitude to reciprocate the pump and thereby incrementally increase the pump output pressure to the set point value. A electric motor driven diaphragm pump has been shown in the prior art. A electric motor used as driving device for a diaphragm pump is commonly a stepping motor or a DC motor (Direct Current motor). When a stepping motor is used, discharge of the pump is controlled by means of controlling a rotation speed of the stepping motor by modifying frequency or duty ratio of applied pulses to the stepping motor. Although discharge of the pump is accurately regulated by the stepping motor, as shown in Fig. 7 depending on the duty ratio of pulses, discharge of the pump is so largely changed that is not applicable to a diaphragm pump for small amount metering. Furthermore, a stepping motor and a pulse frequency modulating device or a pulse duty control device are expensive and the weight of these devices are heavy. In Fig.7, the relationship between a rotation speed of a stepping motor and discharge of a diaphragm pump is illustrated in the case of setting a pulse width(PW1) at 40ms, 100ms and 200ms. In the case of using a DC motor for driving a diaphragm pump, the DC motor is applied direct current at a constant voltage to be rotated at constant speed, thereby the diaphragm pump discharges continuously constant amount of fluid. A flow control valve is required to be provided in a line after the discharge port of the diaphragm pump for metering a amount of fluid. Moreover, when a DC motor runs continuously, the temperature of the motor becomes high as shown on the curve A in Fig. 6. The curve A illustrates the changing temperature of a DC motor when it runs at 3,600 rpm (applied 2V DC). Another controlling device for a DC motor as an actuator of a diaphragm pump is to regulate rotating amount of the DC motor by application of pulses. When applying pulses, a DC motor rotates intermittently and pumping pressure of a diaphragm pump is controlled by varying applied pulse voltage, and discharge per pumping cycle is regulated by modulating the duty ratio of applied pulses. In Fig. 6, the curve B shows temperature of a DC motor in this case, the temperature of the motor is not so high but an overshoot at rising and falling period of a pulse (as shown in Fig. 6B) is repeatedly impressed to the DC motor, generating a spark at the commutator of the motor and deposit carbon in a brush contact surface of a commutator. This results in a reduction of the service life of the DC motor. SUMMARY OF THE INVENTION In view of the foregoing, it is the main object of this invention to provide a controlling device for a DC motor for driving a diaphragm pump, in order to supply and control a predetermined small amount fluid in a stable manner and which can prolong the service life of the DC motor while reducing the cost. Another object of the present invention is to provide a controlling device for a DC motor for driving a diaphragm pump, which applies pulses to the DC motor but avoids voltage overshoot when applying the pulse. Discharge of a diaphragm pump is regulated by modifying duty ratio or frequency of applied pulses. The control device for a DC motor of this invention comprises, the features as set forth in claim 1. Preferred embodiments of the present invention may be gathered from the dependent claims. The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. Brief Description of the Drawings Fig. 1 diagrammatically illustrates an embodiment of a metering diaphragm pump controlling system of the present invention. Fig. 2 is a schematic diagram of a circuit which may be employed by the device of Fig. 1, Fig. 3 is a schematic side elevation view of an example of a diaphragm pump. Fig. 4 is a wave form chart of pulse applying to a DC motor. Fig. 5 is a graph showing the relations between discharge and applied pulse duty ratio of a DC motor driving a diaphragm pump in the experiment results of an embodiment of the invention. Fig. 6 is a graph showing the temperature - time relations for a DC motor of the invention and of prior arts. Fig. 7 is a graph showing the relations between discharge and applied pulse duty of a stepping motor driving a diaphragm pump. Description of the Preferred Embodiments The preferred embodiment of this invention will now be described in detail with reference to the accompanying drawings. The diaphragm pump controlling system shown in Fig. 1 is used for a metering injection pump. The diaphragm pump 4 driven by DC motor 5 discharges liquid 3 from a tank into a fluid conduit 1 through a injecting pipe 2. The liquid 3, for example disinfectant, is mixed to flowing water in the conduit 1 at predetermined constant rate. A control device 6 supplies pulses to DC motor 5 and modulates a duty ratio or frequency or voltage of the pulses to regulate discharge of the diaphragm pump 4. A flow sensor or pressure sensor 7 is provided in the conduit 1 for detecting a flow amount in the conduit 1 and detected signals are supplied to the control device 6. A control device 6 includes a circuit as shown in Fig. 2 . The circuit comprises a pulse generating integral circuit 6a having an astable multivibrator, a pulse-width modulator VR2, a frequency modulator VR1, an amplifier transistor TR and a variable voltage setting integral circuit 6b having a shutdown circuit. The voltage setting integral circuit 6b is used for setting a pulse-base voltage VCC2 and a pulse voltage VCC1 of a pulse from the pulse generating integral circuit 6a. A diaphragm pump as shown in Fig. 3 comprises a housing member 11, a diaphragm 12, a valve body 13 with valves 14, 14' mounted thereon, and a head member having a suction port 15 and discharge port 16. The diaphragm 12 is fixed to a holder 17 which is connected to a link rod 18. The link rod 18 has a ring portion in which a crank shaft 19 is rotatably supported. In operation of the diaphragm pump controlling system in Fig 1, a desired discharge per a pumping cycle and desired pumping pressure are regulated by setting a pulse duty ratio and a pulse voltage by means of a modulator VR2 and a voltage setting integral circuit 6b, furthermore, a desired discharge per 1 minute is regulated by setting a frequency by means of a modulator VR1 and a bias voltage, as pulse-base voltage, is set by means of a voltage setting integral circuit 6b. The pulse-base voltage has a such level that the DC motor 5 is not rotated. Then, the control device 6 supplies the pulses to the DC motor 5, the DC motor 5 rotates and torque of the DC motor 5 is transmitted to the crank shaft. 19 of the diaphragm pump 4 to reciprocate the link rod and the diaphragm 12. The disinfectant 3 in the tank is suctioned from the suction port 15 and is discharged into the fluid conduit 1 through the discharge port 16 and the pipe 2. The disinfectant 3 is mixed to water flowing in the conduit 1 at a predetermined ratio. If desired, the detected signal of the flow sensor 7 is supplied to the control device 6, the control device modulates pulse (PW1,PW2,VCC1 as shown Fig.4) automatically depending on the detected signal to regulate discharge of the diaphragm pump 4, thereby discharge of the disinfectant 3 is proportioned to flow amount of water in conduit 1. By means of the control device 6 setting a pulse-base voltage, approximately 1.0 V in this embodiment, a bias voltage can applied to the DC motor 5, even when the DC motor 5 is not rotated. This makes it possible to prevent an overshoot high voltage from occurring at rising and falling edges of a pulse and to reduce a rushing high current applied to the DC motor 5. Fig. 5 is a graph showing the relation between discharge and a pumping cycle in accordance to pulse-width in the experimental results of this embodiment. In Fig.5, the vertical axis represents discharge of the diaphragm pump 4 and the horizontal axis represents a pumping cycle, each of four curves is in the case of DC motor 5 supplied of pulse-width at 10ms (milli second),15ms, 18ms and 20ms. It can be understood that discharge of the diaphragm pump 4 is increased at a substantially constant in proportion to pulse-width, in the range of from approximately 2.0 cc/min. to 20.0 cc/min. The DC motor used in the experiment is a ordinary DC motor having a commutator, such the DC motor can be used for driving a metering diaphragm pump which continuously regulates discharge, when using the control device 6 of this invention. Fig. 6 is a graph shown the relation between the temperature and running time of the DC motor 5. In Fig.6, the curve represented by the symbol A is in the case of supplying direct current at a constant voltage of 2V to the DC motor, the curve represented by the symbol B is in the case of supplying pulses which are modulated a pulse voltage 4V ( VCC 1) and pulse-base voltage 0V (VCC2, non bias voltage ),the curve represented by the symbol C is in the case of this embodiment of this invention, supplying pulses of 4V(VCC1) and 1V (VCC2). The curve A shows the temperature of the DC motor rises up to 56°C in short running time at 3600rpm. The curve B shows the temperature of the DC motor rises to 39°C at running time of 280hrs, but pules waveform applied to the DC motor as shown in Fig. 6 B, high voltage overshoot generates at pulse rising and falling points and a spark occurs at a brush contacting surface of a commutator to deposit carbon at the commutator. The curve C shows the temperature characteristics in the case of this invention where a bias voltage is applied to the DC motor at such a level that the DC motor is not rotated, applied pulse waveform is shown in Fig.6 C, a overshoot is restricted It is clear from these curves and the waveforms that the temperature of the DC motor of this invention is controlled to approximately half the temperature of the A type as known prior art, and a overshoot high voltage is restricted to approximately 2/3 that of the B type with no bias voltage applied. As described above, it is evident that the controlling device for a diaphragm pump of the present invention is to provide an arrangement that a discharge of diaphragm pump is accurately regulated in stable manner, through the use of a ordinary DC motor with commutator and a simple controlling circuit which includes a pulse generating means and voltage setting means. Furthermore, according to the control device of the present invention, a overshoot high voltage generating when applying a pulse to a DC motor is restricted by means of a control circuit including a applying means a bias voltage to a DC motor so that a DC motor has a long service life. While the invention has been described in detail and with reference to specific embodiment thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined by the appended claims.

Claims: A control device (6) for a DC motor (5) with a brush commutator for driving a crankshaft (19) of a diaphragm pump (4), comprising: a pulse generating circuit means (6a) for generating and supplying an electrical pulse to said DC motor (5); characterized by a voltage setting circuit means (6b) connected to said pulse generating circuit means (6a) for setting a variable voltage (VCC1) of the electrical pulse and applying a pulse-base bias voltage (VCC2) to said DC motor (5) at a level such that said DC motor (5) is not rotated when no electrical pulse is applied. A control device according to claim 1, wherein said bias voltage (VCC2) is less than 2V. A control device according to claim 1 or 2, wherein said pulse generating circuit means (6a) comprises a pulse generating integral circuit including an astable multivibrator, wherein said voltage setting circuit means (6b) includes a voltage setting integral circuit for setting the bias voltage (VCC2) applied to said DC motor (5) and the pulse voltage (VCC1) of the electrical pulse. A control device according to claim 3, wherein said control device (6) further comprises an amplifying circuit (TR) connected between said pulse generating integral circuit (6a) and said voltage setting integral circuit (6b).

Inventors: AONUMA SABURO, AONUMA, SABURO
Applicants: SATACO CO LTD, SATACO CO., LTD.
Application year: 1999
Main classification: F04B49
IPC codes: F04B43, F04B49