Abstract:
A positioning system includes an actuator, valve (preferably pneumatic), position sensor and an electronic valve controller, integrated in a single unit. Continuously variable setpoints are possible within the range of operation. A preferred control circuit includes a signal converter, a ramp generator to smooth the shape of the command or target value signal applied, a position feedback sensor to report the actual position of the actuator, a controller, and a driver, containing an H-bridge, for controlling the pneumatic valve which feeds air into the actuator mechanism. Integration of all these components into a single unit shortens signal paths, improves resistance to electrical noise, and permits faster response time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. §119(e) of provisional application Ser. No. 60/603,453, filed Aug. 20, 2004, the entire content of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to positioning systems and, more particularly, to a pneumatic control valve, for driving an actuator mechanism, which has an electronic feedback control closely integrated with the control valve. We call such a device an “integrated actuator.” 
       BACKGROUND  
       [0003]     There are several so-called “integrated actuators” which contain the elements of a valve, fluid power cylinder, and even a sensor, but these prior art products are not in fact fully integrated. Examples include products offered by Enfield Technologies, assignee of the present invention, as well as those from other vendors such as Norgren or Allen Air.  
         [0004]     There are also examples of vendors that provide some or all of these elements as individual items or in various forms of sub-assembly which can be assembled as a construction of separate components, but none are unified into a single product and offered as such. Examples include Bimba, Dyval (Parker Hannifin), Festo, Hoerbiger-Origa, and Si-Plan Electronics, Ltd., as well as in research laboratories such as at Vanderbilt, UC Berkeley, and McMaster to name a few academic institutions who have constructed such systems.  
         [0005]     However, none provide for fully integrated on-board closed-loop signal processing and control. The commercial need for such a fully integrated product has not been recognized by others working in the art, and the technical challenges to constructing such a device have been formidable. The present invention has overcome these technical challenges.  
         [0006]     Industry standard practice has been to configure systems with control systems and power drivers physically separate from actuators. This holds true for both fluid power (hydraulic and pneumatic) systems as well as electromechanical systems (such as linear motors and rotary motor/leadscrew drives).  
         [0007]     The challenges have included: the number of valve and valve control devices required to create such a system, and coordination of those devices, control electronics small enough to be placed on-board the actuator itself, and schemes to provide command signals without degradation.  
       SUMMARY OF THE INVENTION  
       [0008]     Accordingly, we have invented a fully integrated position, pressure (including vacuum), or force control system, allowing continuously variable set-points within the respective range of operation, containing the following key performance elements (components or sub-systems): 
        a fluid power actuator (pneumatic or hydraulic; linear or rotary),     actuator sensors (position, pressure, and/or force),     a fluid power valve (pneumatic or hydraulic; standard or proportional),     valve controller electronics (integrated driver/controller),     internal wiring and plumbing for valve, actuator, controller, and sensors,     encased as a single unit with interfaces for fluid media source (compressed air or pressurized hydraulic fluid), command signals (position, pressure, and/or force set points), and human interfaces (switches and indicators).        
 
       ADVANTAGES OVER THE PRIOR ART  
       [0015]     We have recognized the need for such a fully integrated product, and have overcome the challenges to construction of such a device. Additional advantages of such a fully integrated system include: ease of specification and application design, simplified installation and maintenance procedures, and unified components protected from damage and environment.  
         [0016]     Advantages of the pneumatic system of the present invention, compared with prior art hydraulic systems include; the use of clean, more readily available and familiar compressed air, and size and weight. Advantages with respect to electric motor systems specifically include the ability to achieve higher forces for equivalent physically sized systems.  
       BRIEF FIGURE DESCRIPTION  
       [0017]      FIG. 1  is a perspective view of an integrated pneumatic valve, actuator, and valve controller according to the invention;  
         [0018]      FIG. 2  is a simplified schematic diagram illustrating the principal elements of the integrated device of  FIG. 1 ;  
         [0019]      FIG. 3  is a block diagram showing elements of a control circuit for use in the invention;  
         [0020]      FIG. 4  is a more detailed diagram of the input signal converter or conditioner of  FIG. 3 ;  
         [0021]      FIG. 5  is a more detailed diagram of the ramp generator of  FIG. 3 ;  
         [0022]      FIG. 6  is a more detailed diagram of the convergence controller of  FIG. 3 ; and  
         [0023]      FIG. 7  is a more detailed diagram of the valve driver of  FIG. 3 .  
     
    
     DETAILED DESCRIPTION  
       [0024]      FIG. 1  shows a preferred embodiment of an integrated pneumatic valve, actuator, and valve controller according to the present invention. A primary application for such a device is to position some object (not shown) which is coupled to a free end of an actuator rod  1 . In  FIG. 1 , the free end is shown at left. A right end of rod  1  is coupled to a piston (not visible in this view) in a conventional manner.  
         [0025]     Actuator rod  1  is essentially cylindrical, and slides in and out of an actuator air cylinder  3 , which preferably is also a cylinder, having a larger diameter than rod  1 . A feedback sensor inside actuator cylinder  3  reports the position of rod  1  to a valve controller  6  which controls a pneumatic valve  13  to modify air pressure within cylinder  3 , in order to adjust the linear position of rod  1  with respect to cylinder  3 . There is an annular air space inside cylinder  3  between a front cap  2 , near the free end of rod  1 , and a mounting plate  4  which is essentially perpendicular to a major axis of cylinder  3 .  
         [0026]     Pneumatic valve  13  can supply air pressure to a right end of cylinder  3 , for example via a port in plate  4 , to cause rod  1  to extend, and can supply air pressure to a left or front end of cylinder  3 , to the left of the piston, for example via tubing to a port  15  adjacent front cap  2 , to cause rod  1  to retract.  
         [0027]     A back cap  7  is arranged essentially parallel to front cap  2  and mounting plate  4 , with pneumatic valve  13  and its valve controller  6  arranged between mounting plate  4  and back cap  7 . For example, a horizontal mounting plate  5 , supported between back cap  7  and mounting plate  4 , can support the valve and valve controller. A wiring harness  12  provides electrical connections between the position sensor, valve  13 , valve controller  6 , and other elements. Back cap  7  can be equipped with an electrical power switch  9 , a compressed air input port  10 , and a compressed air exhaust port  8 , preferably having a muffler to reduce noise.  
         [0028]     The general principle of positioning servo-mechanisms, namely providing a target or command value of position of an actuator, sensing an actual value of actuator position, and attempting to drive the actuator until the actual value matches the target value, is well known in both the pneumatic arts and other branches of engineering. Various types of position sensors are likewise well known, as are the advantages/disadvantages of particular sensor types for particular engineering applications. Historically, one problem with pneumatic positioning servo-mechanisms has been that locating electrical controllers at a distance from the valve and/or from the position sensor(s) renders the signal paths between the elements vulnerable to amplitude drops, electrical noise, and transmission delay. Therefore, the present invention shortens the signal paths by integrating the control electronics with the valve and actuator.  
         [0029]      FIG. 3  illustrates a preferred control circuit. A target or command value signal, in the form of a voltage value in the range 0-10 volts or a current value in the range 0-20 milliAmps, is applied to a signal converter  30 . An actual actuator position feedback signal is received from a position sensor. The output signal from signal converter  30  is fed, depending upon the setting of a switch  35 , either directly to one input of a controller  50 , or via a ramp generator  40  to controller  50 . Use of a ramp generator as part of the invention is optional, but is preferred because it changes an abrupt “steplike” variation in the target value signal to a sloped or more gradual signal pattern, permitting smoother movement of the valve and actuator elements.  
         [0030]     Controller  50  compares the feedback or actual actuator position signal to the target or command signal, and generates an output signal which is applied to the input of valve driver circuit  60 . Valve driver circuit  60  has two terminals +Ic and −Ic which are coupled to respective terminals of a voice coil inside pneumatic valve  13 . Valve  13  is preferably a spool-and-sleeve valve, structured as disclosed in BORCEA et al. U.S. Pat. Nos. 5,460,201 and 5,960,831, the disclosures of which are hereby incorporated by reference. A preferred embodiment is a 5-port, 4-way electrically actuated directional control valve.  
         [0031]      FIG. 4  is a more detailed diagram of signal converter  30 . A positive command signal comes in on line  31  and a negative command signal comes in on line  32 . These lines can be connected via a resistor  34  by closing a switch  33 . An output from a variable resistor  36  is applied to a positive input terminal of a first op-amp  37 , whose output is coupled back to its negative input. This serves to pull up the voltage on positive line  31  to a minimum value set at  36 . The output of first op-amp  37  is coupled to the positive input of a second op-amp  38 , whose negative input is coupled via a resistor to input signal  32 . The output of second op-amp  38  constitutes the signal output  39  of signal converter  30 .  
         [0032]      FIG. 5  is a more detailed diagram of ramp generator  40 . At lower left, signal  39  from converter  30  comes in, and is applied to the positive input terminal of a third op-amp  41 , whose output is applied to the positive input terminal of a fourth op-amp  42 . The negative input terminal of third op-amp  41  is also connected back via a resistor to its output. The output of fourth op-amp  42  is also coupled via a different resistor to the negative input of third op-amp  41 . The positive input terminal of fourth op-amp  42  is also coupled via a switch  43  to a bank of parallel-arranged capacitors  44 , whose other terminal is grounded. The function of the capacitor(s) is to charge up in response to a sudden rise in output voltage from op-amp  41  or to discharge in response to a sudden drop in output voltage from op-amp  41 , thereby turning a “steplike” voltage change into a “ramped” voltage change, as previously described, and softening the abruptness of actuator rod motion. The slope of the ramp depends upon which capacitance is selected by switch  43 . The negative input terminal of fourth op-amp  42  is connected via a resistor  45  to the line  46  connecting the output of  42  back to the negative input of op-amp  41 . The output of fourth op-amp  42  constitutes the ramp output  49  which is then applied to the “target value” input of controller  50 .  
         [0033]      FIG. 6  is a more detailed diagram of controller  50 . Ramp output signal  49  comes in at top left and is applied, via a resistor  51  to the positive input of a fifth op-amp  52 , whose negative input is coupled via a resistor  53  to actual actuator position feedback signal  54 . The positive input of op-amp  52  is also connected via a resistor  55  to ground. The output of op-amp  52  is coupled back via a resistor  56  to its negative input. The output signal from op-amp  52  constitutes the controller output signal  59  which is applied to the input of valve driver  60 .  
         [0034]      FIG. 7  is a more detailed diagram of the valve driver  60 , which includes an H-bridge circuit for controlling the driving current applied to first and second terminals  61  and  62  of a voice coil inside control valve  13 . The H-bridge consists of four transistors  71 - 74 , each of whose gates is controlled by the output of a respective op-amp  71 C,  72 C,  73 C,  74 C. Only two of the transistors conduct at a given time. When transistors  71  and  72  are conductive, current flows from V+ via transistor  71  and node  75  to into voice coil terminal  62 , out voice coil terminal  61  and back via node  76  and transistor  72  to ground. This is one direction of current flow. For current flow through the voice coil in the opposite direction, transistors  73  and  74  must conduct. Then, current flows from V+ via transistor  73  and node  76  into voice coil terminal  61 , and back out from terminal  62  via node  75  and transistor  74  to ground.  
         [0035]     The lower half of  FIG. 7  shows the control of the H-bridge transistors. Controller output signal  59  is applied to the positive inputs of op-amps  73 C and  74 C and to the negative inputs of op-amps  71 C and  72 C. A signal from node  75  is applied via a resistor  77  to the positive input of a sixth op-amp  78  and via resistors  79  and  80  of the negative input of op-amp  78 . Resistor  79  is in the path between node  75  and terminal  62 , while resistor  80  is in the path between terminal  62  and op-amp  78 . The output of op-amp  78  is coupled via a resistor  81  back to its negative input. The output of op-amp  78  is also coupled via a resistor  82  to the negative input of a seventh op-amp  83 , whose positive input is grounded. Op-amp  83  is connected in parallel with a variable resistor  84 . The output terminal of op-amp  83  and one terminal of variable resistor  84  are connected to a node  85 . The voltage at node  85  is connected to the positive input of op-amp  71 C and to the negative input of op-amp  73 C. Thus, when the voltage at node  85  goes high, op-amp  71 C turns on transistor  71  and op-amp  73 C turns off transistor  73 . Conversely, when the voltage at node  85  goes low, op-amp  71 C turns off transistor  71  and op-amp  73 C turns on transistor  73 . The positive input of op-amp  72 C and the negative input of op-amp  74 C are connected to ground. In this manner, the value of output signal  59  of controller  50  determines whether current is applied to the voice coil terminals  61 ,  62  and in which direction.  
         [0036]     Various changes and modifications are possible within the scope of the inventive concept. For example, a hydraulic valve, rather than a pneumatic valve, could be used. Further, a rodless cylinder, rather than a single rod cylinder, could be used. Therefore, the invention is not limited to the specific embodiments shown and described, but rather is defined by the following claims.