GB2167320A - A spray control system - Google Patents

Abstract

A spray control system comprising a pneumatically controlled needle valve (4) for regulating the flow rate of sealant supplied to a spray nozzle (2) and an on-off valve within the spray nozzle (2). Atomising air and fan air supplied to the spray nozzle (2) are also controlled by proportional control valves (12) and air jets are used to deflect the spray of sealant emitted by the spray nozzle (2). The spray nozzle may be mounted on a robot arm and the system controlled by a computer (7). <IMAGE>

Description

SPECIFICATION A spray control system This invention relates to a spray control system, for instance a system controlling the spraying of material such as a sealant over a joint.

Known spray control systems employ complicated mechanisms for controlling a valve which regulates the flow of material. These systems are usually specially designed for a particular application and are thus expensive and are restricted to a particular mode of operation.

According to this invention there is provided a spray control system comprising: a dispensing unit incorporating an on-off valve for dispensing material through a spray nozzle; a flow rate control valve for controlling the rate of the flow of material supplied to the dispensing unit; spray fan adjustment means for controlling the spray emitted from the spray nozzle; and control means for controlling operation of the two valves and the spray adjustment means to regulate operation of the system.

Preferred features of the invention will be apparent from the subsidiary claims of the specification.

The invention will now be described, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a box diagram showing the construction of a preferred embodiment of a spray control system according to the invention; and Figures 2A, B, and C illustrate the operation of a preferred form of spray nozzle of the system.

Figure 1 shows a dispensing unit 1 with a spray nozzle 2 positioned above the surface of a component 3 onto which adhesive is to be applied. The dispensing unit 1 incorporates a first on-off valve (not shown) which may be a pneumatically controlled plunger. The dispensing unit 1 is connected to a pneumatic proportional flow rate control valve 4 by a flexible hose 5. The proportional flow rate control valve 4 receives a supply of pressurised sealant from a supply container (not shown) via a main pump 6 such as an air driven reciprocating pump. The sealant is supplied at a pressure within the range 1000 to 3500 Ibs/in2 (70-240 bar). Control means for controlling operation of the proportional flow rate control valve 4 comprises a computer control 7 connected via a first interface 8 to an I/P converter 9.The I/P converter 9 converts electrical signals from the interface 8 to pneumatic signals which are used to control the proportional flow rate control valve 4. The I/P converter 9 is connected to a pressurised air supply between 20 and 100 Ibs/in2 (1.4-7 bar) via a first filter/water trap 10 and a first air regulator 11. The computer control 7 also controls operation of the on-off valve incorporated in the dispensing unit 1.

The dispensing unit 1 is connected to receive atomising air for atomising the sealant in the spray nozzle from a proportional air control valve 12. This valve receives a supply of pressurised air via a second filter/water trap 13 and a second air regulator 14 and is controlled by the control means by means of a 0800 mA signal received from the computer control 7 via a second interface 15. The pressure of the atomising air supplied to the dispensing unit is thus controlled by the valve 12 in proportion to the magnitude of the signal received from the second interface 15. A second on-off valve is provided in the atomising air supply, preferably in the dispensing unit 1.

The dispensing unit 1 is optionally connected to receive fan air for altering the shape of the fan of atomised sealant emitted from the spray nozzle 2. The fan air is received from a proportional fan air control valve connected to a source of pressurised air via a further filter/water trap and further air regulater under the control of a further interface connected to the computer control 7. These components are shown by dotted lines in Figure 1 and are arranged in a similar manner to the corresponding components supplying atomised air to the dispensing unit 1. A further on-off valve would also be provided in the fan air supply, again preferably in the dispensing unit 1.

The dispensing unit may also be provided with a side deflector nozzle 6 positioned adjacent the outlet of the spray nozzle 2. Air may be simply supplied to the deflector nozzle via another on-off valve connected to a regulated pressurised air supply or via another proportional control valve similar to those used to supply the atomising air and the fan air and an on-off valve in the dispensing unit 2. The deflector nozzle and its operation will be described in more detail below with reference to Figures 2A, B, and C.

The system illustrated in Figure 1 is particularly suitable for use with a robot (not shown) and for applying sealant over a joint between parts of a component such as a vehicle door.

The dispensing unit 1 is mounted on a robot arm (not shown) which is arranged to move the unit 1 around a predetermined path so that sealant is sprayed onto the component 3.

The proportional flow rate control valve 4, the proportional atomising air and fan air control valves and the associated control means are mounted on a static part of the robot to allow for convenient routing of signal and power cables. In use, the robot arm moves the dispensing unit 1 around the predetermined path and the proportional flow rate control valve 4 together with the first on-off valve of the dispensing unit 1 regulate the rate of flow of sealant through the spray nozzle 2 under the control of the control means. The proportional flow rate control valve 4 provides the primary control of flow rate while the first on-off valve provides rapid cut-off of the flow of sealant.

The proportional flow rate control valve 4 is a pneumatically controlled needle valve. The needle is moved by means of a pneumatic piston connected to a pressurised air supply.

Movement of this piston is controlled by a proportional pneumatic power amplifier which is controlled by pneumatic signals in the range 3-15 Ibs/ins2 (0.2-1 bar) received from the I/P converter 9. The proportional flow rate control valve 4 controls the flow rate of sealant from the pump 6 to the hose 5. The shape of the needle valve determines its flow coefficient, ie the rate of flow through the valve at a given setting for material at a given pressure and of a given viscosity. The needle valve is easily replaced so that the flow coefficient and the response speed can be set to suit a particular sealant or a particular application.

The proportional atomising air control valve 12 and the associated on-off valve are controlled by electrical signals from the second interface 15 to regulate the pressure of atomising air supplied to the spray nozzle 2 whereby the form of the spray, ie the size of the droplets within the spray, emitted from the spray nozzle 2 can be controlled. The proportional atomising air control valve 12 provides the primary control of the pressure of the atomising air while the second on-off valve provides rapid cut-off of the air. The proportional fan air control valve and the associated on-off valve are controlled by electrical signals from the further interface to regulate the pressure of fan air supplied to the spray nozzle 2 whereby the form of the spray, ie the shape of the fan produced, emitted from the spray nozzle can be controlled.The proportional fan air control valve provides the primary control of the pressure of the fan air while the further on-off valve provides rapid cut-off of the air.

Advantageously, the computer control 7 is arranged to supply electrical signals corresponding to a number of pre-set flow rates and pressures of atomising and fan air. These signals are typically in the range cf 4-20 mA and 0-800 mA respectively and may conveniently be produced by pre-set potentiometer circuits. Alternatively, a digital to analogue converter may be used. The electrical signals from the first interface 8 are converted into corresponding pneumatic signals in the 3-15 Ibs/in2 (0.2-1 bar) range mentioned above by the I/P converter and control operation of the flow rate control valve 4. The computer control 7 is also arranged to control the signals it supplies to the proportional valves in dependence upon the speed of movement of the robot arm.The robot arm may move more slowly around bends than along straight lines and the computer control 7 makes allowances for these changes in speed to ensure that a uniform quantity of sealant is deposited onto the component 3 in a uniform manner. Alternatively, the computer control 7 may be arranged to vary the rate of flow of sealant through the spray nozzle 2 so that more sealant can be deposited on some areas of the component 3 than on others. The size of the droplets deposited onto the component 3 and the width of the band of sealant formed may also be varied by adjusting the supply of atomising air and fan air appropriately. Ramp generation functions may also be used to gradually open or close the proportional flow rate control valve 4 and the other valves in accordance with acceleration or deceleration of the robot arm.A high level of control of the deposition of sealant onto the component is thus possible. In a typical application, a band of adhesive approximately 20mm in width is formed at a rate of about 300mm/sec. This corresponds to a flow rate of sealant of approximately 1.7 litres/min. The proportional control valves can be controlled independently, interactively or in unison with each other by the computer control 7. A manual override of the automatic system described is preferably provided together with a visual readout of the various parameters.

In a preferred arrangement, the computer control 7 is arranged on start-up to open the on-off valve in the dispensing unit 1 before the proportional flow rate control valve 4 is opened. Similarly, on shut-down the proportional control valve 4 is closed before the onoff valve is closed. By this means, unwanted ejection of sealant due to residual pressure within the hose 5 on start-up or shut-down is avoided. The use of a high pressure hose 5 also helps avoid unwanted ejection of sealant and reduces inherent lags and surges in the system. A high impulse PTFE hose is thus preferably used, for example a hose with an operating pressure of 6000 Ibs/in2 (414 bar) and a minimum burst pressure of 24001bs/in2 (1655 bar) and an internal bore of 6mm or less. The hose 5 is preferably kept as short as possible so the proportional flow rate control valve 4 should be positioned close to the dispensing unit 1. The internal bore of the hose 5 should be kept as small as possible to minimise the effect of its inherent elasticity due to the volume of sealant contained therein.

In a preferred embodiment, a flow transducer (not shown), for instance an ultrasonic transducer, is provided in the dispensing unit 1 to monitor the rate of flow of material through the spray nozzle 2. The flow transducer provides a feed-back signal to the computer control 7 to enable adjustments to be made to automatically compensate for changes such as variations in the material viscosity or variations in pump pressure. Failures such as blockages can also be identified and an alarm given.

Figures 2A, B, and C illustrate the operation of the side deflector nozzle 16. Jets of air are emitted from one or more orifices in the deflector nozzle 16 positioned adjacent the spray nozzle 2 so as to impinge upon the spray of sealant as it is emitted form the spray nozzle 2. These air jets deflect the spray of sealant and cause it to travel sideways with respect to the spray nozzle 2 as shown in Figure 2A. This is of great advantage when sealant is to be deposited onto normally inaccessible areas such as joints behind re-entrant flanges. Figure 2B shows a spray nozzle 2 without a side deflector nozzle and illustrates a situation in which sealant cannot be deposited onto a joint 17 since it is marked by a flange 18.However, as shown in Figure 2C, by using a side deflector nozzle 16, the spray of sealant emitted from the spray nozzle 2 can be deflected sideways under the flange 18 and onto the joint 17.

The spray of sealant emitted from the spray nozzle 2 can be deflected in predetermined directions by providing multiple orifices in the deflector nozzle 16 and directing air jets through one or more of the orifices towards the spray of sealant. As mentioned above, the supply of air to the deflector nozzle can be controlled by an on-off valve supplied with a regulated pressure or via a proportional control valve. With the latter arrangement the deflection angle can also be controlled by adjusting the pressure of air supplied to the deflector nozzle 16. It will be appreciated that when the dispensing unit 1 is mounted on a robot arm, the use the deflector nozzle 16 effectively provides another axis of movement of the arm.

The system has been described above in relation to controlling the flow of a sealant but it can also be used with other fluids such as paints and similar materials.

The system described above can also be adapted to suit a wide range of requirements and can be used with new or existing robot systems.

Claims (13)

1. A spray control system comprising: a dispensing unit incorporating an on-off valve for dispensing material through a spray nozzle; a flow rate control valve for controlling the rate of flow of material supplied to the dispensing unit; spray fan adjustment means for controlling the spray fan emitted from the spray nozzle; and control means for controlling operation of the two valves and the spray adjustment means to regulate operation of the system.

2. A system as claimed in claim 1 in which the spray fan adjustment means comprises atomising air adjustment means for controlling the pressure of air used to atomise material as it is emitted from the spray nozzle.

3. A system as claimed in claims 1 or 2 in which the spray fan adjustment means comprises fan air control means for controlling air supplied to alter the shape of the fan of atomised material emitted from the spray nozzle.

4. A system as claimed in any preceding claim in which the spray fan adjustment means comprises deflector means for controlling the direction in which material is emitted from the spray nozzle.

5. A system as claimed in any preceding claim in which pressurised air is supplied to the or at least one of the spray fan adustment means by a proportional control valve.

6. A system as claimed in claim 5 in which a further on-off valve is provided in the supply of pressurised air downstream of the proportional control valve.

7. A system as claimed in claim 6 in which the on-off valve is within the dispensing unit.

8. A system as claimed in any preceding claim in which operation of the flow rate control valve is controlled by a pneumatic signal and the control means comprises an I/P convertor for producing the pneumatic signal from an electrical signal.

9. A system as claimed in any preceding claim in which the control means comprises a computer for controlling two or more of the valves of the system indepedently, interactively or in unison with each other.

10. A system as claimed in any preceding claim in which the dispensing unit is connected to the flow rate control valve by a flexible hose.

11. A system as claimed in claim 10 in which the dispensing unit is mounted on a robot arm which is movable with respect to a support on which the flow rate control valve is mounted.

12. A system as claimed in claim 4 or any claim dependent thereon in which the deflector means comprises a nozzle positioned to direct one or more jets of air onto material emitted from the spray nozzle.

13. A spray control system substantially as hereinbefore described with reference to the accompanying drawings.