GB2162770A

GB2162770A - A flow control system

Info

Publication number: GB2162770A
Application number: GB08420188A
Authority: GB
Inventors: Michael David Rawle
Original assignee: BL Technology Ltd
Current assignee: BL Technology Ltd
Priority date: 1984-08-08
Filing date: 1984-08-08
Publication date: 1986-02-12
Also published as: GB8420188D0; GB2162770B

Abstract

A flow control system comprising a pneumatically controlled needle valve (4) for regulating the flow rate of adhesive from a pump (6) to a dispensing unit (1) which incorporates an on-off valve. The needle valve (4) and the on-off valve are controlled by a computer control (7) via an I/P converter (9) to regulate the flow of adhesive from the dispensing unit (1). The dispensing unit (i) may be mounted on a robot arm and used to apply a bead of adhesive around the periphery of a component (3) such as a vehicle door skin. <IMAGE>

Description

SPECIFICATION A flow control system This invention relates to a flow control system, for instance a system controlling the flow of a fluid such as an adhesive onto a component.

Known flow 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 flow control system comprising: a dispensing unit incorporating an on-off valve for dispensing material through an outlet; a flow rate control valve for controlling the rate flow of material supplied to the dispensing unit; and control means for controlling operation of the two valves whereby the rate of flow of material dispensed through the outlet is regulated.

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 drawing which is a box diagram showing the construction of a preferred embodiment of a flow control system according to the invention.

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

The system illustrated in the drawing is particularly suitable for use with a robot (not shown) and for applying a bead of adhesive onto a component such as a vehicle door skin. 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 a bead of adhesive is deposited onto the component 3, for instance around the periphery thereof. The flow rate control valve 4 and the 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 flow rate control valve 4 and the on-off valve of the dispensing unit 1 regulate the flow of adhesive through the nozzle 2 under the control of the control means to form a bead of adhesive on the component of a desired diameter, the flow rate control valve 4 providing the primary control of flow rate while the on-off valve provides rapid cutoff of the flow.

The 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 flow rate control valve 4 controls the flow rate of adhesive from the pump 6 to the hose 5. The shape of the needle valve determines its flow co-efficient, 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 adhesive or a particular application.

Advantageously, the computer control 7 is arranged to supply electrical signals corresponding to a number of pre-set flow rates. These signals are typically in the range of 4-20 mA and may conveniently be produced by pre-set potentiometer circuits. Alternatively, a digital to analogue converter may be used. The electrical signals from the computer control 7 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 valve 4 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 adhesive is deposited onto the component 3. Alternatively, the computer control 7 may be arranged to vary the diameter of the bead so that more adhesive can be deposited on some areas of the component 3 than on others. Ramp generation functions may also be used to gradually open or close the flow rate control valve 4 in accordance with acceleration or deceleration of the robot arm.

A high level of flow regulation is thus possible. In a typical application, a bead of adhesive approximately 6mm in diameter is formed at a rate of about 300mm/sec. This corresponds to a flow rate of adhesive of approximately 0.5 litres/min. A manual override of the automatic system described is preferably provided together with a visual readout of the flow rate.

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 flow rate control valve 4 is opened. Similarly, on shut-down the control valve 4 is closed before the on-off valve is closed. by this means, unwanted ejection of adhesive due to residual pressure swithin 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 adhesive 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 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 adhesive 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 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 block- ages can also be identified and an alarm given.

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

A spray nozzle (not shown) can optionally be fitted to the dispensing unit 1 to atomise material as it is dispensed. This is particularly useful when the described system is used to apply a sealant as used to seal the joint between two components of a vehicle body, or to apply paints or similar materials.

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

Claims

1. A flow control system comprising: a dispensing unit incorporating an on-off valve for dispensing material through an outlet; a flow rate control valve for controlling the rate flow of material supplied to the dispensing unit; and control means for controlling operation of the two valves whereby the rate of flow of material dispensed through the outlet is regulated.

2. A system as claimed in claim 1 in which the flow rate control valve is a needle valve.

3. A system as claimed in claim 2 in which the control means comprises a pneumatic piston for opening and closing the needle valve.

4. A system as claimed in claim 3 in which operation of the pneumatic piston is controlled by a pneumatic signal.

5. A system as claimed in claim 4 in which the control means comprises an I/P converter for producing the pneumatic signal from an electrical signal.

6. 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.

7. A system as claimed in claim 6 in which the dispensing unit is mounted on a robot arm which is moveable with respect to a support on which the flow rate control valve is mounted.

8. A system as claimed in any preceding claim comprising a flow rate monitor for monitoring the flow rate of material through the outlet and for providing a feed-back signal to the control means.

9. A system as claimed in any preceding claim in which the dispensing unit dispenses material through a spray nozzle.

10. A system as claimed in any preceding claim which is arranged to dispense material at a plurality of predetermined flow rate as determined by the control means.

11. Asystem as claimed in claim 10 in which the control means comprises a plurality of potentiometer circuits which are pre-set to provide signals corresponding to the predetermined flow rates.

12. A system as claimed in claim 7 or any claim dependent thereon in which the control means is arranged to regulate the rate of flow of material dispensed through the outlet in dependence upon the speed of movement of the robot arm.

13. A system as claimed in any preceding claim in which on start-up the on-off valve is opened before the flow rate control valve is opened.

14. A system as claimed in any preceding claim in which on shut-down the flow rate control valve is closed before the on-off valve is closed.

15. A flow control system substantially as hereinbefore described with reference to the accompanying drawing.