Servo valve

A positive pressure operated servo apparatus for lateral alignment of a continuous web of paper, plastic, textiles and other materials which are being processed at windup, unwind, printing, coating, folding and slitting stations, or other intermediate points in the machine process. The apparatus includes an air source communicating with a sensor and servo valve which regulates a double-acting air actuator having an output member to move a web positioning assembly. The servo valve is regulated by a diaphragm that is controlled by a pneumatic correction signal force from a low pressure sensor circuit and is arranged under the influence of such signal force to selectively position a valve element relative to two orifice openings to provide differential air pressure proportional to error to operate the actuator to produce actuator movement proportional to the error to correct and maintain the position of the web.

BACKGROUND OF THE INVENTION 
This invention relates to new and useful improvements in pneumatic servo 
valves used with automatic web guiding systems. 
Automatic web guiding systems are used to control the lateral position of 
moving webs of material, such as paper, plastics, textiles and other 
flexible materials being processed in continuous or roll form. A signal is 
generated by the position of the web edge relative to a sensor, and the 
signal output either directly controls an actuator connected to 
positioning means or indirectly controls an actuator through a servo valve 
which is connected to a web positioner. Positioners maintain the edge of 
the web at a desired location. 
Various types of mechanical servo valves have been incorporated into 
automatic web guiding systems to control the operation of actuator means. 
As shown in U.S. Pat. No. 5,664,738 utilizes a pneumatic system having a 
feeler type sensor that rides on the web edge and incorporates a rotary 
valve that opens and closes over two matching orifices, limitations of 
this valve are due to the "feeler" being restricted to use on light 
plastic films and flimsy webs because of its mass. U.S. Pat. No. 4,609,012 
is another pneumatic system having a moving suspension valve with two 
matching recesses that are spaced above a stationary block providing four 
way portage for proportional pneumatic flow for controlling actuator 
means. Due to the design of this valve it is limited in velocity and 
force, and uses excessive air. as well as being costly to manufacture and 
assemble. Both pneumatic systems are used in conjunction with double 
acting actuators. 
The idea of spool type servo valves is not new or unique to automatic web 
guiding. Systems have incorporated four way hydraulic valves, providing 
proportional flow across the valve to a double acting actuator means. This 
system usually incorporates a low pressure, non contact pneumatic sensor 
which is highly desirable for sensing thin, delicate webs, that would 
resist direct contact from "feeler" type sensor. 
Most all-pneumatic systems have not used spool type servo valves due to air 
loss across valve and lack of ability to achieve proportional stable 
control and web guiding accuracy. Air tight sealing would be needed to 
achieve control force at the actuator, which would create excessive 
friction by the sliding spool assembly, resulting in sticking or inability 
to generate adequate signal force, system stability and accuracy would be 
jeopardized, as well as excessive air usage. 
SUMMARY OF THE INVENTION 
According to the invention and forming a primary objective thereof, a low 
friction servo valve is provided with spool lands that close-off air flow 
over two exhaust orifices, as one orifice is opened to allow air to 
exhaust, the other is closed to provide pressure to one side of a double 
acting actuator, this procedure is reversed to allow force to the opposite 
side of actuator means. This improved use of air flow makes this valve 
highly responsive as to velocity and force output, as well as control 
accuracy and minimal air consumption. 
Another object of the invention is to provide a valve of the type described 
that is capable of precise and accurate manufacture that is low cost and 
easily assembled and maintained. 
Another objective of the invention is to incorporate a non-contact low 
positive air flow sensor which generates a signal force from lateral web 
movement as edge regulates air recovery across two opposing orifices. This 
non contact sensor is highly desirable for use with webs that are flimsy, 
such as plastic films and textiles, as well as a variety of relative stiff 
webs. 
Another objective of the invention is to supply a spool valve that has 
lands that are slightly spaced from walls of the valve body to eliminate 
friction, as well as using low coefficient of friction bearings as support 
journals for reducing friction and holding valve alignment. This carefully 
constructed valve should not be subject to sticking. Valve is spring 
loaded from each end to allow biasing so that signals received from the 
sensor equalizes cylinder shifting speed. The exhaust orifices are sized 
and shaped to provide guiding accuracy and good system response. 
Another objective of the invention is to provide a needle valve to adjust 
air supply force to the sensor to either increase or decrease velocity of 
signal to diaphragm means. 
Another objective of the invention is to have two matching orifices in the 
air pressure supply force to reduce air usage and give good efficient 
operation of air supply. 
Another objective of the invention is to adjust supply air pressure to 
increase or decrease actuator velocity and control force. 
Another optional objective of the invention is to supply air pressure 
independently, through use of two independent air supplies, to sensor or 
diaphragm side of servo valve and control or actuator side. This allows an 
increase in control force to actuator means without effecting the signal 
force. 
The purpose of this invention are accomplished by utilizing an air pressure 
source, such as a compressor, which is connected to a double acting, 
pneumatic actuator engaged to laterally move either the unwind or 
rewinding rolls or intermediate web positioning guide roller equipment in 
response to signal pressure changes. The signal force from the sensor is 
impinged directly upon a neoprene diaphragm which pilots a spool flow 
valve that is enclosed in a housing that has a pair of matching orifices 
facing the inner surfaces of two lands of the valve spool. As valve is 
opened to exhaust air from one orifice, second orifice is closed to supply 
control force to one side of a double acting cylinder. As signal force 
from sensor is reversed control valve reverses over the two valve exhaust 
orifices, opening the closed exhaust orifice and closing the other to 
control power to the actuator means. When both exhaust orifices are closed 
simultaneous, system is in a null position with no cylinder movement in 
either direction. This occurs when web is on track and no lateral movement 
is detected at sensor. 
The invention will be better understood and additional objectives and 
advantages will become apparent from the following description taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF DRAWINGS 
Referring to FIG. 1, the apparatus of the pneumatic web guide system of the 
present invention is used in association with a moving web indicated 
generally at 10. Such a web may be in the form of paper, tape, cloth, foil 
plastics or other flexible materials. By way of example, the web 10 may 
move longitudinally between a supply roll 12 and a take up roll 13. During 
such movement, the web may shift laterally because of misalignment of the 
material wound on the roll 12. Such misalignment of the web 10 can be 
adjusted or corrected by shifting the supply roll 12 laterally in 
proportion to the sensed misalignment. This forms the guide means for 
correcting the path of the web 10. Also, the lateral position of web can 
be corrected at intermediate points of the moving web by changing the 
angular position of a guide roller (not shown) in contact with the web 10. 
Such guide rollers form parts of web guide arrangements for maintaining 
webs in a predetermined path and are available commercially in many forms. 
The lateral position of the web 10 is controlled automatically by a web 
control system. The principle components of which are an air compressor 18 
for a continuous supply of compressed air, a double acting actuator 20 
operatively connected to supply roll 12 to move it axially and a servo 
valve assembly 22 and sensor 24 which responds to the lateral position of 
the web 10 to control the operation of the actuator 20 to bring about 
corrective movement of the roll 12 and therefore the lateral position of 
web 10. The actuator 20 is of the double acting type and incorporates a 
moveable wall in the form of a piston 26 in a cylinder 28 and forming a 
pair of air pressure chambers 30 and 32 at opposite sides of the piston 
26. The piston 26 is connected through a rod 34 to various linkages and 
mechanism indicated generally at 35 to bring about lateral movement of the 
supply roll 12. A variety of apparatus responsive to the movement of an 
actuator 20 is available to bring about such corrective movement of a 
supply roll 12. Similarly, actuator 20 can be used in association with 
rewind rolls or web guide mechanism at intermediate points of a web (not 
shown). 
The output of the compressor 18 is supplied through a conduit 36 and 
through a pressure regulator 38, to port connector 84 on port plate 46, 
(see FIG. 2) of the servo valve assembly. 
The sensor 24 is mounted in a fixed but adjustable position relative to the 
edge of the web 10. The sensor 24 is connected pneumatically through 
branch conduits 40 and 42 to the servo valve 22. 
The embodiment of the servo valve comprises a sensor port plate 46, in turn 
connecting to actuator port plate 48 and diaphram housing 50 and 52 
respectively. Actuator port plate 48 is secured to valve body 54 by screws 
124. 
Referring to FIG. 2, a housing 50 is secured to sensor port plate 46 and 
valve body 54 by screws 126 and 128 respectively, and a housing 52 is 
secured to the rear of housing 50 as by screws 130. These housings 50 and 
52 connect to a portion of the sensor port plate 46 and have cooperating 
cavities 96 and 97 (FIG. 2) to form a diaphragm chamber enclosing a thin, 
flexible diaphragm 106 securely clamped between the upright housings. The 
diaphragm 106 has a reinforcing body portion 55 integral therewith. Body 
portion is connected to valve shaft 56 end by screw 58. Valve shaft ends 
extend through two low friction support bearings 60 and 62 which provide 
alignment and support. Each end of valve shaft 56 is spring engaged 64 and 
66. Spring 66 is a biasing spring and is made variable in its force by an 
adjustment screw 68 in the front end plate 70. Front end plate 70 is 
coupled to valve body by screws. Valve shaft 56 supports spool 72, which 
is laterally adjustable, having spool lands 132 and 134 forming closures 
over matched and sized exhaust vent orifices 74 and 76. Normally, spool 
length is set to slightly close off both vent orifices. This spool length 
determines the accuracy or response of the system. The spool lands 132 and 
134 extend slightly past exhaust orifice openings 74 and 76 to act as an 
air flow restriction at one orifice, as the other orifice is vented during 
operation through ports 78 or 80. A minute spacing exists between valve 
spool lands 132 and 134 and valve body 54, thus eliminating metal to metal 
contact and possible spool sticking. Two separate spools could be used and 
spaced apart over exhaust orifice openings 74 and 76, which could be 
adjusted to reduce control accuracy and system response. Spool movement is 
reversed when web edge direction is reversed at sensor 24. 
Operation of the servo valve is accomplished by an air supply from a 
suitable compressor 18, through a conduit 36 to a pressure regulator 38, 
supplying a continuous supply of forced air to connecting port 84, in the 
sensor port plate 46 through passageway 82, which simultaneously supplies 
air to sensor 24 and actuator 20. 
Air supply to the sensor 24 is accomplished by flow in passageway 82 being 
regulated by variable restricting valve 92 through passageway 93 through 
conduit 40 to one side of the sensor 24 through a orifice and across web 
edge 10A. Also, in inlet passageway 82 is a fixed orifice 94, which 
supplies air simultaneously to the diaphragm cavity 96 and through conduit 
42 to the opposite side of the sensor 24, and to an orifice directly 
opposing the other sensor orifice and outward to the web edge, and 
atmosphere (FIGS. 9 and 10). Movement of the diaphragm is generated from a 
signal at the sensor when web moves laterally from a null position. 
Essentially, valve 22 is in a null position when web edge 10A is not 
moving laterally at sensor and spool lands 132 and 134 are balanced over 
exhaust orifices 74 and 76 of the valve. 
FIGS. 9 and 10, Sensor 24 generates a signal force by air recovery from the 
nozzle pressure 40 across the web edge 10A to the low pressure (Signal 
Pressure) side of the sensor 24. Air is partially being blocked by web 
edge 10A when spool 72 of the servo valve 22 is in a null position. 
Supply air through connecting port 84 that is routed through passage 82 of 
the sensor port plate 46 is simultaneously ported through conduit 86 to 
two fixed orifices 88 and 90, the restricting effect of these orifices 
reduces air consumption and communicate with matched ports 98 and 100 of 
the actuator port plate to two slight recesses 120 and 122 spaced above 
exhaust orifice 74 and 76 in the valve body 54 to provide quick signal 
response from the sensor 24 to the actuator means. Air vents through the 
valve body 54 through ports 78 and 80 to the atmosphere and through sensor 
to the atmosphere. 
The opening and closing of exhaust orifices 74 and 76 provide air flow 
through connecting ports 98 and 100 to connecting ports 102 and 104 to the 
conduits 108 and 110 to actuator 20 which forms a wall of air for driving 
the actuator piston 26 to control web positioning assembly. For example, 
if the web 10 should move to the right as viewed in FIG. 2, the higher 
nozzle pressure, at the sensor 24 will be recovered at the lower, signal 
pressure side 42 of the sensor, moving the diaphragm 106 to the right, 
driving the spool valve assembly 72 to the right, the spool valve closes 
over the right exhaust orifice 76 routing air flow through conduit 108 to 
actuator air chamber 30, driving piston 26 left and air flow from chamber 
32 through exhaust orifice 74 to the atmosphere. Piston rod 34 moves the 
supply roll 12 axially to the left to its original path. As the web 10 
approaches its original lateral position, the web edge 10A partially 
blocks the air flow of conduit 40 and signal pressure causing the 
diaphragm 106 to move spool valve 72 to the original null position, 
closing exhaust orifice 74 and 76 with lands 132 and 134 respectively to 
restrict air from exhausting from the servo valve. 
If the web 10 should stray in the opposite direction, that is to the left, 
as viewed in FIG. 1, sensor 24 engaged with web edge will move the 
diaphragm to the left, driving the spool valve assembly left to increase 
the size of exhaust orifice 76 and increase the overlap of the closed 
orifice 74. This results in a greater pressure in actuator chamber 32 than 
in actuator chamber 30 so that the piston 26 moves toward the right as 
viewed in FIGS. 1 and 2 to bring about rightward movement of the web 10 to 
its original position. 
The resistance to movement of spool valve shaft 56 is substantially the 
same in opposite directions and as a result, the pressures are decreased 
or modulated in one chamber 30 or 32 to bring about the necessary 
corrective movement of the actuator 20. As a consequence, control of 
movement of the web is equal in opposite directions. 
Fixed restricting orifices 88 and 90 located in the actuator port plate 48, 
are sized equally to provide uniform pressure levels in each line 108 and 
110, therefore, in the chambers 30 and 32 of the actuator 20 to maintain 
minimal air supply usage and position of the supply roll 12 in the 
necessary location to establish the predetermined path of the web. 
Once the restricting orifices 88 and 90 are sized to determine the null 
point at the sensor and reference point of the web, the pressure regulator 
38 can be adjusted to select the pressure of the system. By way of 
example, the pressure regulator 38 could be set at 10 psi when the force 
required to bring about corrections in the positions of the web path of 
the web are relatively low and at some higher level, such as 20 psi, for 
example, when larger corrective force of the actuator 20 is needed. At any 
system pressure level the corrections made to the path of the web are 
proportional to the movement of the web from its selective path and are 
equal in opposite directions. 
A web guide system has been provided which relies on a web position sensor 
which moves a control valve to modulate the exhaust pressure from one 
chamber or the other of a double-acting actuator which moves in response 
to the differential pressure to bring about corrective movement to the web 
with such corrective movement being equal to the amount of the error. 
The sensor regulates the diaphragm pressure by providing nozzle pressure 
recovery across web edge to an opposing lower signal pressure side of the 
sensor. These pressures are supplied by the same pressure source as the 
control pressure side of the servo valve, variable restricting valve 92 
provides an adjustable supply pressure to the nozzle, high pressure, side 
of the sensor 24 and which also communicates with passageway 82 having a 
flow restricting orifice 94 that communicates with conduit 42 that 
connects to the signal side of the sensor, providing a low pressure 
signal, providing a response pressure to the diaphram cavity 96 and servo 
valve diaphragm to bring about corrective means to a double-acting 
actuator. Both sensor and servo valve, as well as actuator, use an 
interconnected air source without the need of any electrically or 
hydraulically controlled components. 
There are several important design features of the servo valve, the valve 
spool 72 having lands 132 and 134 which are suspended a minute clearance 
less than the circular inner wall 112, of the valve body 54, while 
providing a fairly good seal for air flow at the same time provides free 
movement of the valve shaft 56 and spool 72 assembly from a signal force 
impinged on the diaphram. The only friction generated is by two valve 
shaft support bearings 60 and 62 of narrow width, made of low friction 
material for ease of movement. The valve ports 78 and 80 are mounted in a 
downward position to expel oil or water that may come into the valve with 
the air supply. The valve is highly responsive to the low signal pressure 
impinged on the diaphram, requiring only about +/-0.002 inch web 10 
movement from a null position to cause modulation of the valve. Also, low 
signal pressure at the sensor enables detection and control of very light 
webs, such as plastic films and textile material. 
The unique, simple design of the port plate and valve assembly enables 
minimal air consumption with a high degree of performance, fixed orifices 
88 and 90 throttle air supply to valve exhaust vent orifices 74 and 76, 
which are blocked by the valve spool lands 132 and 134 when in a null 
position. When valve orifice is open air exhaust from one side through one 
of two valve ports. The closed exhaust orifice directs supply pressure to 
the actuator means. Total air consumption for sensor and control side of 
servo valve is about 2 cfm at pressures between 10 and 30 psi at 
regulator. 
Due to the simplicity of design of the invention, cost is greatly reduced 
over other more costly web guide systems. Two of the four basic components 
are drilled through from one end. Actuator port plate 48 is plugged at one 
end 118. This plug can be removed if required. Valve is easily assembled 
in minimal time. 
A web guide system has been provided which relies on a web position sensor 
providing a flow of air which is in direct contact with the edge of a web 
to directly move a control valve to modulate the exhaust pressure from one 
chamber or the other of a double-acting actuator which moves in response 
to the differential pressure to bring about corrective movement to the web 
with such corrective movement being equal to the amount of error. The only 
components required are a servo valve, sensor and a double-acting actuator 
and a source of air pressure interconnected by air lines without the need 
of any electrically or hydraulically controlled components or servo 
mechanisms. 
Although the servo valve has been described for use with a double acting 
actuator means, a single acting actuator with a spring return could be 
substituted. 
Although the invention has been described as having a single supply of air 
18, two independent sources of air could be used, namely a source for the 
pneumatic actuator 20 and a source of air for the sensor 24. 
Although the valve has been described for use with air, other gasses and 
liquids could also be used.