GB2094411A

GB2094411A - Method and Circuitry for operating an armature driven spray gun

Info

Publication number: GB2094411A
Application number: GB8107310A
Authority: GB
Original assignee: Brennenstuhl Hugo & Co KG GmbH
Current assignee: Brennenstuhl Hugo & Co KG GmbH
Priority date: 1981-03-09
Filing date: 1981-03-09
Publication date: 1982-09-15
Also published as: GB2094411B

Abstract

In order to reduce the quantity of liquid atomized by a pendulum-type armature driven spray gun within any unit of time, a pulse width modulated excitation signal with steeply ascending slopes is fed into the armature drive unit. The circuit in one embodiment comprises a drive circuit (20) generating a drive signal with steeply ascending slope and a controllable switch (18) connected between a supply voltage source (16) and the armature drive unit, the control terminal of the switch (18) being connected to the output of the drive circuit (20). <IMAGE>

Description

SPECIFICATION Method and circuitry for operating an armature driven spray gun The invention relates to a method and circuitry for operating a pendulum-type armature driven spray gun.

Penduium-type armature driven spray guns are provided with a pump plunger of piston movable in a pump cylinder, the piston being biased towards a suction position by means of a spring and being moved against the pressure of the spring by means of an electromagnet, in order to deliver the liquid which has been drawn into the gun spray head. The pump piston, the armature of the electromagnet and the spring, together form a system capable of oscillation, which is continuously supplied with the energy consumed in atomizing the liquid from the mains AC supply.

The spray output, i.e. the quantity of liquid atomized per unit of time, of known spray guns, can be adjusted by limiting the suction stroke of the pump piston by means of an adjustable mechanical stop. In this way, output can be reduced to a minimum of around 300 g/min, since any further reduction of the suction stroke would prevent the perfect atomization of the liquid.

It is an object of the present invention to provide a method and circuitry for operating a pendulum-type armature driven spray gun, which would ensure good atomization even at low spray output.

The spray output of pendulum-type armature driven spray guns has so far been adjusted by adjusting the suction stroke end and the delivery stroke end, selected independent of spray output, perhaps in accordance with the viscosity of the liquid to be atomized in certain cases where the pump piston has been responsible for positive actuation of a delivery side non-return valve.

According to the present invention there is provided a method of operating a spray gun, the method comprising energizing a pendulum-type armature drive unit of the spray gun by providing therefor a pulse width modulated excitation signal with steeply ascending slope, in order to reduce the quantity of liquid atomized within any unit of time.

The present invention also provides circuitry for operating a spray gun, the circuitry comprising means for generating a signal with steeply ascending slope, and means for controlling the application of the signal to a pendulum type armature drive unit of the spray gun for energising the latter.

The technique is based on a fixed predetermined end point of the suction stroke, while changing the end point of the delivery stroke by adjusting the rms power supplied to the pendulum-type armature drive unit. In this way the piston can deliver very small quantities of liquid in each stroke, by being stopped shortly after that point in time at which it passes the suction port located in the side of the pump cylinder. The high pressure required for fine atomization of the liquid at the spray head is nevertheless ensured, since the pendulum-type armature drive is energized with impulses with steeply ascending slopes, which ensure correspondingly abrupt piston acceleration.

A significant advantage is the considerable reduction in operational noise and the improved constancy of the set spray output. In known spray guns, the armature linked to the pump piston tends to run hard against the fixed stop at the end of the suction stroke, resulting in a rather unpleasant rattling noise. This hard impact may even alter the adjustment of the stop itself, tending to increase spray output, which would be extremely undesirable in cases where a fine coating is to be produced.

Preferably the pendulum-type armature drive unit is energised by a pulse width modulated excitation signal with steeply descending slope.

This ensures a particularly abrupt stop of the pump plunger. In this way, the spray output may be adjusted to an extremely small quantity, while nevertheless ensuring that the necessary high pressure is built up in the head of the spray gun during the pump piston rapid movement between abrupt acceleration and abrupt stopping.

Preferably also the steep slopes are produced by switching an input signal changing slowly in comparison with slope time. This has the advantage of particularly simple application, using generally available sources of voltage supply.

Suitable sources are the usual AC mains supply or DC sources.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic representation of a pendulum-type armature driven spray gun and an associated operating circuit according to a first embodiment; Fig. 2 is a representation similar to Fig. 1, according to a second embodiment; and Fig. 3 is a circuit diagram for a pendulum-type armature driven spray gun.

Referring to the drawings, Fig. 1 shows, in diagrammatic form a spray gun 10 with a pendulum-type armature drive unit, not illustrated in detail, which acts on a pump plunger or piston longitudinally movable within a pump cylinder. In the side of the pump cylinder, a suction port is provided, which communicates with a reservoir 12 for the liquid to be atomized by way of a suction pipe. On the suction side of the pump consisting of the pump piston and pump cylinder, no separate suction valve is provided, the pump operating with slot control by the piston itself on the suction side.

On the delivery side, a non-return valve is incorporated in the pump cylinder, by way of which the liquid is delivered to a spray head 1 4.

These details of the pump and of the pendulumtype armature drive unit are not shown in the drawing, since they are known as such.

An operating circuit for the spray gun 12, which circuit is represented in the form of a block diagram in Fig. 1, comprises a supply voltage source 16, a controllable switch 1 8 and a signal generator 20. The supply voltage source 20 is preferably a DC source, such as a battery or a power unit with rectifier. The signal generator 20 has adjustable pulse width and, in addition, preferably adjustable frequency. The controllable switch 18 can be a transwitch, in particular a power transistor or thyristor. These electronic components are known as such, and various models are commercially available and need here not be described in further detail.

The assembly illustrated in Fig. 1 operates as follows: the signal generator 20 produces a square wave pulse with steeply ascending and descending slopes. This drive signal, which is produced with a minimum of power, serves to modulate the input voltage available at the switch 1 8. In this way, the excitation signal for the spray gun, being the output signal of the switch 1 8, has the same frequency and the same pulse-duty factor (cycle/pulse width) as the drive signal, however combined with high power. In the field coil of the spray gun's penduium-type armature drive unit, a magnetic field is thus built up and reduced in rapid alternation, ensuring corresponding abrupt acceleration and braking of the pump piston.The amplitude of the pump delivery stroke can be reduced by increasing the pulse-duty factor of the drive signal, thus simultaneously and correspondingly reducing the energy supplied to the pendulum-type armature drive while still achieving an extremely rapid buildup and reduction of the magnetic field. In order to ensure better adaptation to the dynamic properties of the pendulum-type armature drive and the pump at low amplitudes, the frequency of the drive signal can be slightly altered at the same time as the pulse-duty factor. In practical applications, frequency can be positively coupled with pulse-duty factory modifications, e.g. by mechanically coupling two pulse width and cycle potentiometers of the square wave signal generator.

Fig. 2 shows an operating circuit similar to the circuit of Fig. 1, in which, however, the supply voltage source and the controllable switch are replaced by a power amplifier 22, which amplifies the drive signal emitted by the signal generator 20 to provide the excitation signal for the spray gun 10. As far as the results are concerned, the operating mode of this circuit corresponds to that of the operating circuit according to Fig. 1.

Fig. 3 shows details of an operating circuit as used in the embodiment of Fig. 1, the supply voltage source being represented by the AC mains terminals 24, 26.

The controllable switch in this case is a thyristor 28 in series connection with a coil 30 of the pendulum-type armature drive and with a manually operated main switch 32. The gate terminal of the thyristor 28 is connected by way of a double diode 34 to a phase shifting potential divider circuit with a series circuit connected across the mains terminals 24, 26 and consisting of an adjustable resistor 36 and a capacitor 38, the latter being bridged by a further series circuit consisting of a resistor 40 and a capacitor 42. The network junction point between the resistor 40 and the capacitor 42 represents the output of the phase shifting potential divider circuit and is connected to the double diode 34.

By adjusting the resistor 36, the phase angle at which the thyristor 28 drives can be adjusted. At this point, voltage is applied to the coil 30 with steeply ascending slope, resulting in rapid acceleration of the pump piston. By increasing the angle at which the thyristor 28 drives, the pulseduty factor can be increased and the amplitude of the pump piston stroke reduced. Since phase angles between 15 and 1700 are possible in practical application, the stroke of the pump piston can obviously be adjusted within a very large range.

The operating circuit illustrated in Fig. 3 can easily be incorporated in the housing of a spray gun in addition to the pendulum-type armature drive unit.

If the thyristor 28 is replaced by a triac, the pendulum-type armature unit can be driven with twice the frequency of the AC network.

Claims

1. A method of operating a spray gun, the method comprising energising a pendulum-type armature drive unit of the spray gun by providing therefore a pulse width modulated excitation signal with steeply ascending slope, in order to reduce the quantity of liquid atomized within any unit of time.

2. A method according to claim 1 , wherein the pendulum-type armature drive unit is energised by a pulse width modulated excitation signal with steeply descending slope.

3. A method according to claim 1 or 2, wherein the steep slopes are produced by switching an input signal changing slowly in comparison with slope time.

4. A method according to any of claims 1 to 3, wherein the spray output is reduced by increasing the pulse-duty factor of the pulse width modulated signal while maintaining the amplitude thereof.

5. Circuitry for carrying out the method according to any of the preceding claims the circuitry comprising a drive circuit generating a drive signal with steeply ascending slope, and a controllable switch connected between a supply voltage source and the pendulum-type armature drive unit, a control terminal of the switch being connected to the output of the drive circuit.

6. Circuitry according to claim 5, wherein the supply voltage source is an AC source and the drive circuit has a phase shifting circuit connected to the AC source, the controllable switch comprising a thyristor or a triac.

7. Circuitry according to claim 6, wherein a double diode is connected between the output of the phase shifting circuit and the control terminal of the thyristor or the triac.

8. Circuitry according to claim 5, wherein the drive circuit is formed by a square wave signal generator or by a ramp generator.

9. Circuitry according to any of claims 5 to 8, wherein a manually operated switch is connected in series with the controllable switch.

10. Circuitry for carrying out the method according to any of claims 1 to 4, the circuitry comprising a signal generator producing a drive signal with steeply ascending slope and a power amplifier, the output of which is connected to the pendulum-type armature drive unit.

11. Circuitry for operating a spray gun, the circuitry comprising means for generating a signal with steeply ascending slope, and means for controlling the application of the signal to a pendulum type armature drive unit of the spray gun for energising the latter.

12. A method of operating a spray gun substantially as hereinbefore described with reference to the accompanying drawings.

1 3. Circuitry for operating a spray gun substantially as hereinbefore described with reference to the accompanying drawings.

14. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.