GB2068150A

GB2068150A - Automatic control of fluid motor speed

Info

Publication number: GB2068150A
Application number: GB8034305A
Authority: GB
Original assignee: Ransburg Corp
Current assignee: Ransburg Corp
Priority date: 1980-01-18
Filing date: 1980-10-24
Publication date: 1981-08-05
Also published as: IT8167049A0; DE3101193A1; JPS56121654A; HK28588A; CA1154844A; GB2068150B; BE886934A; IT1143276B; DE3101193C2

Abstract

A feedback system for controlling the speed of a fluid motor (10), preferably an air motor, includes an optical-signal transmitter (44), an optical-signal receiver (46), and an optically sensitive marker (30,36) on the motor output shaft (12). The marker selectively couples the optical- signal transmitter to the optical- signal receiver and converted into an electrical signal at 58 indicative of motor speed. This signal is compared with a desired speed signal set by control 68 in the circuit 62 and supplied converter (84) which converts the signal to a fluid signal. A processor (104,112) is coupled to the converter for processing the fluid signal to provide a processed fluid signal which is coupled to the input of the fluid motor to control it. The motor speed is displayed at 76. <IMAGE>

Description

SPECIFICATION A feedback system for controlling the speed of a motor This invention relates to motor-speed controls, and specifically to a feedback speed-control system for a fluid motor such as that described in, for example, United States Patent Application Serial No. 13,125, filed February 21, 1979, titled ROTATING ATOMIZING DE VICE, and assigned to the same assignee as this application.

Various types of coating material atomizing device drive mechanisms are known. There are, for example, the drive mechanisms of the following United States Patents: Juvinall et al, U.S. Patent 2,759,764; Juvinall, U.S. Patent 2,754,226; Simmons, U.S. Reissue Patent 24,602; Wirth, U.S. 3,358,931; Hechenbleikner, U.S. Patent 1,853,682; and Kent et al, U.S. Patent 3,011,472. Many coating devices are known which are adapted to be driven by fluid motors, such as air motors.

There are, for example, the systems of the following United States Patents: Sigvardsson et al, U.S. Patent 3,067,949; Wampler et al, U.S. Patent 3,121,024; and Allander, U.S.

Patent 2,711,926. The increasing use of such fluid motors is attributable, in part, to the ease with which the rotational speeds of atomizing devices driven by such motors can be varied by varying the fluid pressures to the inputs of such motors.

However, an undesirable characteristic of such fluid motors is that changes in certain characteristics of coating materials being dispensed from the atomizing devices coupled to such fluid motors can cause significant variations in the rotational speeds of such atomizing devices by changing the loads of such fluid motors. This is particularly true of very low horsepower (e.g., fractional horsepower) fluid motors, such as the turbine-air motor described in the above-identified U.S. Patent Application Serial No. 13,125.

Generally, such changing characteristics of the coating materials which are being atomized include changes in viscosities, solids contents, specific gravities, and the like, of the coating materials. Unfortunately, in many situations, for example where color changes are carried out between the finish coating of successive articles on a production line, the very act of changing the color of the coating material results in a substantial change in these characteristics. This occurs simply because it is not always possible to match every pertinent characteristic of every different coating material which is being used on the line. This results unavoidably in changes in the loads on the fluid motors which are atomizing these various coating materials with many of the changes in coating material color.

As an example, on an automobiie finishcoating line, each car to pass along the finishcoating line will typically be coated with a finish having a different color from the color applied to the next preceding car, and from the color to be applied to the next succeeding car. Several systems for controlling such color changes which take into account, and adjust for, many aspects of coating material variation from color to color have been proposed. There is, for example, the system described in United States Patent Application Serial No.

35,105, filed May 1, 1979, titled ANALOG PAINT OUTPUT CONTROL, and assigned to the same assignee as the present invention.

This system describes in detail the control of such parameters as coating material flow rate and coating material pressure to account for certain characteristics of different coating materials where coating material changes (e.g., color changes) are being conducted on, for example, a production line.

It is an object of the present invention to provide a system for controlling the speed of a drive motor for an atomizing device associated with such a production line, with the motor speed being controlled to account for variations in the characteristics of coating materials which are being atomized by the atomizing device. With respect to "variations of coating material characteristics" from coating material to coating material, what is meant is that the load on the motor which drives the atomizing device from which the atomized coating material is dispensed changes with such coating material characteristic variations. Accordingly, the motor input must be changed to maintain the motor speed constant under such changing load conditions.

According to the invention, a feedback system for controlling the speed of a fluid motor having a motor fluid input includes an opticalsignal transmitter, an optical-signal receiver, means providing an optically sensitive marker, and means for coupling the marker to the motor in driven engagement. The marker functions selectively to couple the optical transmitter signal to the optical-signal receiver. This provides an optical output signal indicative of motor rotation. The system further includes means for converting the opticaloutput signal to a fluid signal, and means for coupling the converting means to the motor input to control motor speed.

According to an illustrative embodiment of the invention, the means for coupling the converting means to the motor input includes means for processing the fluid signal to develop a processed fluid signal. The processed fluid signal is fed to the motor input.

According to an illustrative embodiment of the invention, the motor includes an output shaft and the means providing the optically sensitive marker includes a wheel, the means for coupling the marker to the motor includes means for mounting the wheel on the motor output shaft, and the wheel further includes means for providing a pattern on one of its surfaces. The optical-signal transmitter includes means for directing an optical signal onto the pattern. The optical-signal receiver includes means for detecting refiections of the transmitted optical signal from the pattern to provide the optical output signal.

According to an illustrative embodiment, the means for converting the optical output signal to a fluid signal includes an optical pulse counter for counting optical-output signais to generate electrical signals indicative of motor revolutions, a clock for generating a time base, a signal processor, and means for coupling the optical pulse counter and clock to the signal processor to generate a signal indicative of motor revolutions per unit time.

The converter means further includes means for displaying motor revolutions per unit time, and means for coupling the display means to the signal processor to provide a visual indication of motor speed.

Additionally, in an illustrative embodiment, the signal processor includes a control input for permitting selective adjustment of the motor speed. Such selective adjustment can be provided either by an analog signal or by a digital signal, depending upon the specific requirements of the processor. The illustrative signal processor further includes a comparator for comparing the signal indicative of motor revolutions per unit time with the control input and for generating a comparator output signal.

The system further includes means for converting the comparator output signal into the fluid signal and means for coupling the converter to the comparator. The converter is also coupled to a source of fluid in the illustrative system, the converter acting to convert the comparator output signal to the fluid signal.

In the illustrative system, a fluid-signal amplifier is provided, along with means for coupling the fluid-signal amplifier to a source of driving fluid for the motor, to the fluid-motor input, and to the converter. The fluid-signal amplifier acts under the influence of the fluid signal from the converter to control the flow of motor driving fluid from the driving fluid source to the motor input to control motor speed.

The system may best be understood by referring to the following detailed description and accompanying drawing which illustrates the invention The drawing is a block and schematic diagram of a feedback system constructed according to the present invention for controlling motor speed.

In the drawing, a fluid motor 10 of the type described in the above-identified application Serial No. 1 3,1 25 includes an output shaft 1 2 upon which is mounted an atomizing device 1 4. Device 14 may be any of several suitable types such as, for example, the type described in United States Patent 4,148,932.

A feed tube 1 6 feeds a coating material from a selected one of a number of sources (not shown) through a source control (not shown) to the interior of atomizing device 14, from which the coating material is atomized in a pattern 1 8 and deposited onto a target 20, an article to be coated by the material. It is to be understood that the target 20 can be moving, for example, along an assembly line, and that motor 10 need not necessarily be stationary.

That is, motor 10 can be mounted, for example, on a ram associated with a fluid cylinder which projects the motor 10 and atomizing device 1 4 into close proximity to the target 20 before coating material is dispensed. Typically, the system also includes a source 24 of electrical potential for electrostatically charging and aiding in the atomization of particles of coating material in the pattern 1 8. In such a system, the target 20 will be maintained at a potential, here ground 26, to promote migration of the charged particles of coating material in pattern 1 8 toward the target 20. This greatly enhances the efficiency of coating of the target 20 and reduces coating material waste.

A wheel 30 is mounted on the output shaft 12, illustratively on the inside of the motor 10 housing 32. It is to be understood that wheel 30 need not be a component which is added to motor 10. In fact, in an air-driven turbinetype motor of the type described in the aboveidentified application Serial No. 13,125, the wheel 30 can be the turbine wheel of the motor 10 itself. A marker pattern 36 is provided on wheel 30. Pattern 36 includes areas 38, 40, readily distinguishable from one another by an optical-signal transmit-receive head 42.

Head 42 includes an optical transmitter 44, such as an optical fiber 45 which conducts light from a light source, and an optical-signal receiver 46 mounted within housing 32 in close proximity to one another and in an orientation such that the receiver 46 detects movement of the pattern 36 as areas 38, 40 move beneath the optical-signal transmit-receive head 42. The pattern 36 can consist simply of light and dark areas 38, 40, respectively, which, respectively, reflect and absorb light from transmitter 44 to provide a received (refiected) signal on optical receiver 46 once each rotation of shaft 1 2.

The optical-signal transmit-receive head 42 provides at receiver 46 an output optical signal which is transmitted along an optical fiber 49 in a fiber-optic cable 50 coupled to a light source and receiver 52. The cable 50 in the illustrative embodiment includes fiber 45 which transmits light "down" the cable 50 to transmitter 44, and fiber 49 which transmits received light "up" cable 50 from receiver 46 to the light source and receiver 52. The head 42 and fiber-optic cable 50 are of a type such as the Spectral Dynamics Fiberoptic Cable Model 13134-GPT-1 available from Spectral Dynamics Corporation of San Diego, P.O. Box 671, San Diego, California 92112.

Light source and receiver 52 includes electric circuits responsive to the received light from receiver 46 to generate electrical pulses corresponding to the optical output signal from receiver 46. These electrical pulses are coupled, illustratively, through conductors 56 to a clock, or time-base generator, 58 which generates a time base against which occurrences of shaft 1 2 rotation (as represented by the signal on conductors 56) are compared. A signal indicative of motor 10 revolutions per unit time results on conductors 60. The light source and receiver 52 and clock 58 are available as a unit in, for example, the Spectral Dynamics Corporation of San Diego Model 13135. Conductors 60 couple the signal indicative of motor revolutions per unit time to a feedback comparator and servo drive system 62.The feedback comparator and servo drive system 62 includes an input 64 coupled by a suitable conductor 66 to a control input device 68. Device 68 produces an output signal which is selectively variable in accordance with the desired motor 10 speed. The output signal produced by device 68 on conductor 66 can be either analog or digital, depending upon the nature of device 68, and the nature and requirements of the feedback comparator and servo driver 62.

Feedback comparator and servo driver 62 includes an output 72 which is coupled by conductors 74 to a digital display 76 on which is displayed shaft 1 2 rotations per unit time (e.g., r.p.m.). Feedback comparator and servo driver 62, control input device 68, and digital display 76 are of commercially available type, such as, for example, the Ransburg Corporation. Part Number 20370 Servo Driver; the Beckman 7360 Potentiometer, available from Beckman Instruments Incorporated, Helipot Division, 2500 Harbor Boulevard, Fullerton, California 92634; and the Weston 1 230 Digital Panel Meter, available from Weston Instruments Division, Sangamo Weston Incorporated, 614 Frelinghuysen Avenue; Newark, New Jersey 07114, respectively.

An output 78 from the feedback comparator and servo driver 62 is coupled through conductors 80 to an input 82 of a converter, or transducer, 84 which converts the signal on conductors 80 to a fluid signal at output 88 of transducer 84. A fluid source, such as a source of compressed air 90, is coupled through a conduit 94 to an input 96 of transducer 84. The transducer 84 acts to convert the signal at input 82 to a fluid signal at output 88 by controlling the flow of fluid from source 90 in -response to the input signal at 82.

Output signal 88 is supplied through a conduit 100 to the input 102 of an on-off solenoid valve 1 04. The output 106 of valve 104 is coupled through a conduit 108 to the input 110 of a fluid signal amplifier, or volume booster, 11 2. An additional input 114 of volume booster 11 2 is coupled through a conduit 11 6 to a source 11 8 of driving fluid for motor 1 0. The output 1 20 of volume booster 11 2 is coupled through a conduit 122 to the driving fluid inlet 1 24 of motor 10.

Transducer 84, solenoid valve 104, and volume booster 11 2 are of commercially available types such as, for example, Fairchild Model 5109 Transducer, available from Fairchild Industrial Products Division, 1 501 Fairchild Drive, Winston-Salem, North Carolina 27105; Skinner N.C. Solenoid V53DA2020 24VDC Coil, available from Skinner Electric Valve Division, Skinner Precision Industries Incorporated, 95 Edgewood Avenue, New Britain, Connecticut 06050; and Fairchild Model 20 &num;205103 1:6 Volume Booster, also available from Fairchild Industrial Products Division.

The design of the instant invention is advantageous over other types of feedback control systems for fluid motors in that the element 42 for sensing motor 10 speed does not come into contact with rotating portions, e.g., shaft 1 2 and wheel 30, of the motor 1 0.

Thus, the system of the present invention does not consume part of the motor 10 horsepower output to sense motor 10 speed.

Again, this is particularly significant where low- or fractional-horsepower motors are used to rotate atomizing devices or for other purposes.

Further, by using the fiber-optic cable 50 in the sensing system, it is possible for the device to operate in a hazardous location (e.g., high solvents content atmosphere) without the need for protective sheathing, insulation, or the like. Specifically, the fiber-optic cable 50 permits the monitoring and control of the speed of motor 10, even when the motor 10 is at a high electrostatic potential, e.g., 100 KV, as a result of the action of the electrostatic potential supply 24.

Claims

1. A feedback system for controlling the speed of a fluid motor having a motor fluid input, the system comprising:- an opticalsignal transmitter; an optical-signal receiver; means providing an optically sensitive marker; means for coupling the marker to the motor in driven engagement, the marker selectively coupling the optical-transmitter signal to the optical-signal receiver to provide an optical output signal indicative of motor rotation; means for converting the optical output signal to a fluid signal; and means for coupling the converter to the motor input to control motor speed.

2. A system according to claim 1 wherein the means for coupling the converter to the motor input comprises means for processing the fluid signal to provide a processed fluid signal.

3. A system according to claim 1 or claim 2 wherein the motor includes a motor output shaft and the means providing an optically sensitive marker includes a wheel, the means for coupling the marker to the motor includes means for mounting the wheel on the motor output shaft, and the wheel further including means providing a pattern on one of its surfaces.

4. A system according to any preceding claim wherein the optical-signal transmitter includes means for directing a beam of light onto the pattern.

5. A system according to any preceding claim wherein the optical-signal receiver includes means for detecting reflections of the light beam from the pattern to provide the optical output signal.

6. A system according to any preceding claim wherein the means for converting the optical output signal to a fluid signal includes an optical pulse counter for counting optical output signals and for generating electrical signals indicative of motor revolutions, a clock for generating a time base, a signal processor, and means for coupling the optical pulse counter and clock to the processor to generate a signal indicative of motor revolutions per unit time.

7. A system according to claim 6 comprising means for displaying motor revolutions per unit time, and means for coupling the display means to the signal processor to provide a visual indication of motor speed.

8. A system according to claim 6 or claim 7 wherein the signal processor includes a control input for permitting selective adjustment of motor speed.

9. A system according to any of claims 6 to 8 wherein the signal processor includes a comparator for comparing the signal indicative of motor revolutions per unit time with the control input and for generating a comparator output signal.

1 0. A system according to any preceding claim wherein the means for converting the optical output signal to a fluid signal comprises means for converting the comparator output signal into the fluid signal, and means for coupling the converter to the comparator.

11. A system according to claim 10, comprising means for coupling the converter to a source of fluid, the converter acting to convert the comparator output signal to a signal in the fluid flow from the fluid source to generate the fluid signal.

1 2. A system according to any preceding claim wherein the means for processing the fluid signal comprises a fluid signal amplifier, means coupling the fluid signal amplifier to a source of driving fluid for the motor, means coupling the fluid signal amplifier to the fluid motor input, and means coupling the fluid signal amplifier to the converter, the fluid signal amplifier acting under the influence of the fluid signal from the converter to control the flow of motor driving fluid from the driving fluid source to the motor input to control motor speed.

1 3. A feedback system for controlling the speed of a motor having a motor drive signal input, the system comprising:- an opticalsignal transmitter; an optical-signal receiver; means providing an optical coupler; means for coupling the optical coupler to the motor in driven engagement, the optical coupler selectively coupling the optical-transmitter signal to the optical-signal receiver to provide an optical output signal indicative of motor rotation; means for converting the optical output signal to a motor drive signal; and means for coupling the converter to the motor drive signal input to control motor speed.

14. A system according to claim 1 3 wherein the motor is a fluid motor, the motor drive signal input is a motor driving fluid input, and the drive signal is a fluid signal.

1 5. A system according to claim 1 3 or claim 1 4 wherein the motor includes a motor output shaft and the means providing an optical coupler includes a wheel having an optically sensitive marker provided thereon, and the means for coupling the optical coupler to the motor includes means for mounting the wheel on the motor output shaft.

1 6. A coating material atomizing and dispensing system comprising:- a rotary atomizing device; means for feeding a selected coating material from a selected one of a plurality of sources for such coating materials to the atomizing device; a motor for rotating the atomizing device; and a feedback system for controlling the operating speed of the motor, the system including:- an optical-signal transmitter; an optical-signal receiver; means providing an optical coupler; means for coupling the optical coupler to the motor in driven engagement, the optical coupler selectively coupling the optical-transmitter signal to the optical-signal receiver as the motor operates to provide an optical output signal indicative of motor operation; means for converting the optical output signal to a motor drive signal; and means for coupling the converter to the motor input to control motor speed.

1 7. A feedback system for controlling the speed of a motor, the system being substantially as herein described and shown in the drawing.