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.

FIELD OF THE INVENTION

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

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.

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.

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.

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).

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

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

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.

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

FIG. 1is a perspective view of an integrated pneumatic valve, actuator, and valve controller according to the invention;

FIG. 2is a simplified schematic diagram illustrating the principal elements of the integrated device ofFIG. 1;

FIG. 3is a block diagram showing elements of a control circuit for use in the invention;

FIG. 4is a more detailed diagram of the input signal converter or conditioner ofFIG. 3;

FIG. 5is a more detailed diagram of the ramp generator ofFIG. 3;

FIG. 6is a more detailed diagram of the convergence controller ofFIG. 3; and

FIG. 7is a more detailed diagram of the valve driver ofFIG. 3.

DETAILED DESCRIPTION

FIG. 1shows 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 rod1. InFIG. 1, the free end is shown at left. A right end of rod1is coupled to a piston (not visible in this view) in a conventional manner.

Actuator rod1is essentially cylindrical, and slides in and out of an actuator air cylinder3, which preferably is also a cylinder, having a larger diameter than rod1. A feedback sensor inside actuator cylinder3reports the position of rod1to a valve controller6which controls a pneumatic valve13to modify air pressure within cylinder3, in order to adjust the linear position of rod1with respect to cylinder3. There is an annular air space inside cylinder3between a front cap2, near the free end of rod1, and a mounting plate4which is essentially perpendicular to a major axis of cylinder3.

Pneumatic valve13can supply air pressure to a right end of cylinder3, for example via a port in plate4, to cause rod1to extend, and can supply air pressure to a left or front end of cylinder3, to the left of the piston, for example via tubing to a port15adjacent front cap2, to cause rod1to retract.

A back cap7is arranged essentially parallel to front cap2and mounting plate4, with pneumatic valve13and its valve controller6arranged between mounting plate4and back cap7. For example, a horizontal mounting plate5, supported between back cap7and mounting plate4, can support the valve and valve controller. A wiring harness12provides electrical connections between the position sensor, valve13, valve controller6, and other elements. Back cap7can be equipped with an electrical power switch9, a compressed air input port10, and a compressed air exhaust port8, preferably having a muffler to reduce noise.

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.

FIG. 3illustrates 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 converter30. An actual actuator position feedback signal is received from a position sensor. The output signal from signal converter30is fed, depending upon the setting of a switch35, either directly to one input of a controller50, or via a ramp generator40to controller50. 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.

Controller50compares 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 circuit60. Valve driver circuit60has two terminals +Ic and −Ic which are coupled to respective terminals of a voice coil inside pneumatic valve13. Valve13is 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.

FIG. 4is a more detailed diagram of signal converter30. A positive command signal comes in on line31and a negative command signal comes in on line32. These lines can be connected via a resistor34by closing a switch33. An output from a variable resistor36is applied to a positive input terminal of a first op-amp37, whose output is coupled back to its negative input. This serves to pull up the voltage on positive line31to a minimum value set at36. The output of first op-amp37is coupled to the positive input of a second op-amp38, whose negative input is coupled via a resistor to input signal32. The output of second op-amp38constitutes the signal output39of signal converter30.

FIG. 5is a more detailed diagram of ramp generator40. At lower left, signal39from converter30comes in, and is applied to the positive input terminal of a third op-amp41, whose output is applied to the positive input terminal of a fourth op-amp42. The negative input terminal of third op-amp41is also connected back via a resistor to its output. The output of fourth op-amp42is also coupled via a different resistor to the negative input of third op-amp41. The positive input terminal of fourth op-amp42is also coupled via a switch43to a bank of parallel-arranged capacitors44, 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-amp41or to discharge in response to a sudden drop in output voltage from op-amp41, 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 switch43. The negative input terminal of fourth op-amp42is connected via a resistor45to the line46connecting the output of42back to the negative input of op-amp41. The output of fourth op-amp42constitutes the ramp output49which is then applied to the “target value” input of controller50.

FIG. 6is a more detailed diagram of controller50. Ramp output signal49comes in at top left and is applied, via a resistor51to the positive input of a fifth op-amp52, whose negative input is coupled via a resistor53to actual actuator position feedback signal54. The positive input of op-amp52is also connected via a resistor55to ground. The output of op-amp52is coupled back via a resistor56to its negative input. The output signal from op-amp52constitutes the controller output signal59which is applied to the input of valve driver60.

FIG. 7is a more detailed diagram of the valve driver60, which includes an H-bridge circuit for controlling the driving current applied to first and second terminals61and62of a voice coil inside control valve13. The H-bridge consists of four transistors71-74, each of whose gates is controlled by the output of a respective op-amp71C,72C,73C,74C. Only two of the transistors conduct at a given time. When transistors71and72are conductive, current flows from V+ via transistor71and node75to into voice coil terminal62, out voice coil terminal61and back via node76and transistor72to ground. This is one direction of current flow. For current flow through the voice coil in the opposite direction, transistors73and74must conduct. Then, current flows from V+ via transistor73and node76into voice coil terminal61, and back out from terminal62via node75and transistor74to ground.

The lower half ofFIG. 7shows the control of the H-bridge transistors. Controller output signal59is applied to the positive inputs of op-amps73C and74C and to the negative inputs of op-amps71C and72C. A signal from node75is applied via a resistor77to the positive input of a sixth op-amp78and via resistors79and80of the negative input of op-amp78. Resistor79is in the path between node75and terminal62, while resistor80is in the path between terminal62and op-amp78. The output of op-amp78is coupled via a resistor81back to its negative input. The output of op-amp78is also coupled via a resistor82to the negative input of a seventh op-amp83, whose positive input is grounded. Op-amp83is connected in parallel with a variable resistor84. The output terminal of op-amp83and one terminal of variable resistor84are connected to a node85. The voltage at node85is connected to the positive input of op-amp71C and to the negative input of op-amp73C. Thus, when the voltage at node85goes high, op-amp71C turns on transistor71and op-amp73C turns off transistor73. Conversely, when the voltage at node85goes low, op-amp71C turns off transistor71and op-amp73C turns on transistor73. The positive input of op-amp72C and the negative input of op-amp74C are connected to ground. In this manner, the value of output signal59of controller50determines whether current is applied to the voice coil terminals61,62and in which direction.

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.