Abstract:
An air flow regulator includes a damper ( 14 ) and an air cylinder ( 20 ) operatively connected with the damper ( 14 ) to adjust a damper setting. A pressure sensor ( 52 ) indicates a pneumatic pressure in the air cylinder ( 20 ). An air pressure regulator ( 42 ) is operatively connected with the air cylinder ( 20 ) to pressurize and exhaust the air cylinder ( 20 ) responsive to an electrical input ( 70 ). The air pressure regulator ( 42 ) includes a calibration table ( 64 ) associating steady state air cylinder pressure values with regulator shut-off pressure values. Responsive to the electrical input ( 70 ) updating a steady-state air cylinder pressure value, the air pressure regulator ( 42 ) pressurizes or exhausts the air cylinder ( 20 ) until the pressure sensor ( 52 ) indicates a pressure corresponding to a regulator shut-off pressure value associated in the calibration table ( 64 ) with the updated steady-state air cylinder pressure value, whereupon the air pressure regulator ( 42 ) ceases the pressurizing or exhausting.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/444,074, filed Jan. 31, 2003. 
     
    
     
       BACKGROUND  
         [0002]    The present invention particularly relates to controlled operation of dampers in heating and air conditioning systems, especially high volume air conditioning (HVAC) systems, and will be described with particular reference thereto. The invention relates more generally to controlled operation of air cylinders and pneumatic/mechanical transducer systems, particularly for controlling fluid flow.  
           [0003]    In heating and air conditioning systems, conditioned air is distributed through a house, office building, or other structure through air ducts. Typically, the conditioned air is forced through a duct at a constant air speed, and control of the heating or cooling for a particular room or area of the house, office building, or other structure is effected by partially restricting air flow through a duct using one or more strategically placed dampers.  
           [0004]    The damper setting is typically effected through a pneumatic actuating system that includes an electropneumatic transducer, such as an air cylinder controlled by an electronic air pressure regulator, which operates on the damper. The air pressure regulator pressurizes or exhausts the air cylinder to cause an actuating arm of the air cylinder to move, thus causing the damper setting to be adjusted.  
           [0005]    A problem arises in that air cylinders and other pneumatic devices can exhibit hysteresis, pressure drift, frictional settling delays, and other operating non-linearities and non-regularities. These non-regularities are usually air cylinder-specific, and may be different even for nominally similar air cylinders of the same make and model. Moreover, the operating non-regularities depend upon the operating environment of the air cylinder or other pneumatic device. Thus, the air cylinder characteristics may depend upon the type of damper being controlled, the air flow through the duct, and similar parameters.  
           [0006]    Control of such pneumatic devices is difficult, because the hysteretic, frictional, mechanical or other delays result in long settling times as the air cylinder relaxes to a steady state. During this settling time, the pressure transiently varies in the air cylinder. The air pressure regulator attempts to respond to such transient pressure variations by repeatedly switching between pressurizing and exhausting the air cylinder. This can further increase the settling time, and additionally creates noises that travel through the ducts of the HVAC system and can be disturbing to people in the house, office building, or other structure.  
           [0007]    The present invention contemplates an improved apparatus and method that overcomes the aforementioned limitations and others.  
         BRIEF SUMMARY  
         [0008]    According to one aspect, an air flow regulator is disclosed. A pneumatic cylinder is operatively connected with a damper to adjust a damper setting. A pressure sensor indicates a pneumatic pressure in the pneumatic cylinder. An air pressure regulator is operatively connected with the pneumatic cylinder to pressurize or exhaust the pneumatic cylinder responsive to an electrical input indicative of a selected steady state pressure. The air pressure regulator includes a calibration table associating steady state pneumatic cylinder pressure values with regulator shut-off pressure values. The calibration table is addressed by the electrical input indicative of an updated steady-state pneumatic cylinder pressure value. The calibration table retrieves a shutoff pressure value corresponding to the electrical input. The air pressure regulator ceases the pressurizing or exhausting at the retrieved shutoff pressure value such that the steady state pressure in the pneumatic cylinder settles at about the selected steady state pressure.  
           [0009]    According to another aspect, a method is provided for controlling a pneumatic cylinder which has a lag between termination of pressurization or evacuation and reading a steady state pressure. A desired steady-state pressure is received. A shut-off pressure corresponding to the desired steady-state pressure is retrieved. The shut-off pressure is different from the corresponding steady state pressure. The pneumatic cylinder is pressurized or exhausted. The pressurizing or exhausting is terminated when a measured pneumatic cylinder pressure corresponds to the shut-off pressure.  
           [0010]    According to another aspect, a storage medium encodes instructions executed by a computer or microprocessor to perform a control method for controlling an electropneumatic transducer. The control method includes: constructing a table associating steady state pressures with pressure regulator shutoff pressures; receiving a steady-state pressure value; retrieving a shutoff pressure corresponding to the steady state pressure from the table; and causing a pressure regulator to operate open loop on the electropneumatic transducer until a pressure feedback signal associated with the electropneumatic transducer reaches the retrieved shutoff pressure. Upon the pressure feedback signal reaching the shutoff pressure, the control method causes the pressure regulator to cease operating on the electropneumatic transducer.  
           [0011]    According to yet another aspect, a controller is disclosed for controlling an electropneumatic transducer. An air pressure regulator has a first valve for selectively connecting and disconnecting a pressurized air supply and a second valve for selectively connecting and disconnecting an exhaust. Configurable electronics are configured to receive a steady state pressure, access a configured calibration to obtain a shut-off pressure associated with the received steady state pressure, cause a selected one of the first valve and the second valve to connect, and cause the selected one of the first valve and the second valve to disconnect responsive to an instantaneous pressure corresponding to the obtained shut-off pressure.  
           [0012]    According to still yet another aspect, a method of regulating air flow in a duct system with a pneumatic cylinder controlled damper is provided. An air flow is selected. The selected air flow is converted into a corresponding steady state pneumatic cylinder pressure. A corresponding shutoff pressure is determined from which the pneumatic cylinder will settle at the corresponding steady state pressure. Pressure in the pneumatic cylinder is changed until the shutoff pressure is reached. The pneumatic cylinder is allowed to settle from the shutoff pressure to the steady state pressure corresponding to the selected flow rate.  
           [0013]    One advantage resides in reduced noise during damper operation.  
           [0014]    Another advantage resides in more rapid transient response and reduced settling time for damper setting changes.  
           [0015]    Yet another advantage resides in ready adaptation of the pneumatic control for specific characteristics of the damper, air cylinder, draft characteristics, and other parameters of the air conditioning system.  
           [0016]    Numerous additional advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for the purpose of illustrating preferred embodiments and are not to be construed as limiting the invention.  
         [0018]    [0018]FIG. 1 diagrammatically shows a portion of a high volume air conditioning (HVAC) system including a controlled damper.  
         [0019]    [0019]FIG. 2 shows a flow chart of a preferred method for controlling the damper of FIG. 1.  
         [0020]    [0020]FIG. 3A shows a preferred method for constructing a pressurizing portion of the calibration table of FIG. 1.  
         [0021]    [0021]FIG. 3B shows a preferred method for constructing an exhausting portion of the calibration table of FIG. 1.  
         [0022]    [0022]FIG. 3C shows a preferred method for automatically updating the calibration table of FIG. 1 each time a new damper setting is applied. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    With reference to FIG. 1, a high volume air conditioning (HVAC) system  10  includes a plurality of ducts that convey heated, cooled or otherwise conditioned air throughout a building or other structure. In FIG. 1, the duct system is represented by exemplary duct  12 . At selected places throughout the duct system, dampers are arranged to selectively control air flow. In FIG. 1, the various dampers are represented by an exemplary damper  14 , which is a hinged damper. However, butterfly dampers, louvered dampers, or the like, and various combinations of such dampers, can also be employed. The HVAC system  10  typically further includes selected other components known in the art, such as a furnaces, flues, air conditioning units, particulate filters, registers, return air ducts, and the like, which are not shown in FIG. 1.  
         [0024]    The damper  14  is moved by a pneumatic actuator, which in the exemplary embodiment of FIG. 1 is an air cylinder  20 . The pneumatic air cylinder  20  includes a generally cylindrical body  22  that contains a biased piston  24  that is biased by a compressed spring  26  toward a compressed air volume  28 . In operation, an air line  30  delivers compressed air to pressurize the compressed air volume  28 . The increased pressure drives the piston  24  against the bias spring  26 . To move the piston  24  in the reverse direction, the air line  30  partially or totally exhausts the compressed air volume  28  to reduce the pressure in the compressed air volume  28 . In response to the reduced pressure, the bias spring  26  moves the piston  24  toward the compressed air volume  28 . An actuator arm  32  attached to the piston  24  communicates the linear piston motion of the piston  24  to the damper  14 , where intervening gearing or other mechanical components (not shown) convert linear motion of the actuator arm  32  into movement of the damper  14 .  
         [0025]    The damper  14  is controlled via the air cylinder  20  by a controller  40 , which includes an air pressure regulator  42 . The air pressure regulator  42  includes a first valve  44  that selectively connects the air line  30  with a pressurized air supply  46 . The air pressure regulator also includes a second valve  48  that selectively connects the air line  30  with an exhaust pathway  50 , which in a preferred embodiment exhausts to the ambient air. Alternatively, the pressurized air supply  46  can be replaced by another gas or a liquid (in the latter case providing hydraulic operation), in which case the exhaust pathway  50  is preferably contained. A pressure sensor  52  provides a pressure feedback signal indicative of instantaneous pressure in the air line  30 . As the air line  30  is in continuous fluid communication with the pressurized air volume  28  of the air cylinder  20 , the pressure sensor  52  monitors pressure in the air volume  28  of the air cylinder  20 . Of course, a pressure sensor physically located at and directly monitoring the pressurized air volume  28  can also be employed.  
         [0026]    The controller  40  further includes a processor  60  that selectively operates the valves  44 ,  48  to place the air pressure regulator  42  into one of three states: a pressurizing state in which the first valve  44  is open to connect the pressurized air supply  46  with the compressed air volume  28  of the air cylinder  20  and the second valve  48  is closed; an exhaust state in which the first valve  44  is closed and the second valve  48  is open to connect the compressed air volume  28  with the exhaust pathway  50 ; and an isolation state in which both valves  44 ,  48  are closed to pneumatically isolate the compressed air volume  28  of the air cylinder  20 .  
         [0027]    The processor  60  is suitably a microcontroller, a microprocessor, a computer, or the like, which executes software instructions stored on a non-volatile medium  62  which is suitably embodied as an electronic read-only memory, a Flash memory, a magnetic disk, an optical disk, or the like. In a preferred embodiment the non-volatile storage medium  62  is a programmable read-only memory (PROM), erasable PROM (EPROM), Flash memory, or the like integrated with the processor  60  or connected with the processor  60  by printed circuitry of a printed circuit board. The controller  40  further includes a calibration table  64  which provides a correlation between instantaneous pressures at which the air pressure regulator  42  is placed in the isolation state and corresponding steady state pressures in the compressed air volume  28  of the air cylinder  20 . The calibration table  64  can be stored in a Flash memory, magnetic storage medium, or other read/write-capable non-volatile memory. The processor  60  receives a steady state pressure  70  from the HVAC system controller (not shown) and operates the valves  44 ,  48  to set the air cylinder  20  to that steady state pressure.  
         [0028]    With continuing reference to FIG. 1 and with further reference to FIG. 2, in a preferred embodiment the non-volatile storage medium  62  stores a software program that instructs the processor  60  to cause the controller  40  to perform a control method  100  in response to receiving a new steady state pressure  70 . By comparing the new steady state pressure  70  with the present reading of the pressure sensor  52 , a selection is made  102  as to whether the air pressure controller  42  should act to further pressurize the air volume  28  or to partially or fully exhaust the air volume  28  in order to attain the target steady state pressure  70 .  
         [0029]    As is known in the art, certain pneumatic actuators such as the air cylinder  20  typically exhibit hysteresis, pressure drift, frictional settling delays, and other operating non-linearities and non-regularities. Feedback control of such pneumatic devices typically exhibits long settling times, erratic convergence to steady state, and noisy operation due to repeated pressurizing and exhausting responsive to the non-regularities which are difficult to model and account for within a PID or other conventional control framework.  
         [0030]    To overcome these difficulties, the method  100  employs an open loop control based on parameters stored in the calibration table  64 . In a preferred embodiment which recognizes that the operating non-regularities are generally different for the pressurization and exhausting operations of the air cylinder  20 , the calibration table  64  includes a pressurizing calibration table  64 P and an exhausting calibration table  64 E. The calibration values store shutoff pressure values that correspond to steady state pressure values.  
         [0031]    Thus, for the target steady state pressure value  70  and the selected direction of operation (pressurize or exhaust), a look-up  104  is performed in the appropriate calibration table  64 E (for exhausting) or  64 P (for pressurizing) to obtain a shutoff pressure corresponding to the target steady state pressure  70 . The lookup  104  preferably performs an interpolation between data points of the table  64  to obtain an appropriate shutoff pressure if the target steady state pressure  70  is not one of the data points of the calibration table  64 . Alternatively, the calibration table  64  can be in the form of empirical fitted mathematical expressions for the pressurizing and exhausting correspondence curves.  
         [0032]    A branch  110  of the control method  100  selects the appropriate operation mode of the air pressure regulator  42 : either pressurizing operation or exhausting operation. If pressurizing operation is selected, then in a process operation  112  the pressurized air supply  46  is connected with the air cylinder  20 . This is suitably accomplished by placing the air pressure regulator  42  into the pressurizing state in which the first valve  44  is open to connect the pressurized air supply  46  with the compressed air volume  28  of the air cylinder  20  and the second valve  48  is closed.  
         [0033]    Alternatively, if exhausting operation is selected, then in a process operation  114  the air cylinder  20  is connected with the exhaust pathway  50 . This is suitably accomplished by placing the air pressure regulator  42  into the exhaust state in which the first valve  44  is closed and the second valve  48  is open to connect the compressed air volume  28  with the exhaust pathway  50 .  
         [0034]    Once the appropriate operating state of the air pressure regulator  42  is established, the air cylinder  20  is pressurized or exhausted, causing an increase or reduction in pressure, respectively, over time. At a process operation  120 , the method  100  monitors the instantaneous pressure indicated by the pressure sensor  52  until the instantaneous pressure reaches the shutoff pressure obtained in the lookup operation  104 .  
         [0035]    When the shutoff pressure from the table  64 P,  64 E is reached, the pressurized air supply  46  or the exhaust pathway  50  is disconnected from the air cylinder  20  in a process operation  122 . This is suitably accomplished by placing the air pressure regulator  42  into the isolation state in which both valves  44 ,  48  are closed to pneumatically isolate the compressed air volume  28  of the air cylinder  20 .  
         [0036]    Once isolated, the air cylinder typically exhibits the hysteresis, pressure drift, frictional settling delays, or other operating non-linearities or non-regularities of the particular air cylinder  20 . Such hysteresis, pressure drift, frictional settling delays, or other operating non-linearities or non-regularities are accounted for in constructing the calibration table  64 , so that pneumatic isolation of the air cylinder  20  at the shutoff pressure selected in the lookup operation  104  results in the air cylinder  20  settling in at the target steady state pressure  70 .  
         [0037]    The calibration table  64  is preferably constructed empirically. The various non-linearities and non-regularities of the air cylinder  20  vary from air cylinder to air cylinder. While such non-regularities are usually consistent for a given specific air cylinder, there are commonly substantial variations in the non-regularities between different air cylinders, and even between commercial air cylinders of the same model which are made by the same-manufacturer.  
         [0038]    Moreover, the hysteresis, pressure drift, frictional settling delays, or other operating non-linearities or non-regularities are affected by the environment in which the air cylinder operates. In the exemplary HVAC system  10 , such environmental parameters include air flow in the duct  12 , characteristics of the damper  14 , and mechanical characteristics of the connection between the actuator arm  32  and the damper  14 . Hence, construction of the calibration table  64  is preferably performed in situ, that is, with the air cylinder  20  installed in the HVAC system  10  and connected with the specific damper  14  which is to be actuated.  
         [0039]    With continuing reference to FIG. 1 and with further reference to FIG. 3A, in a preferred method  140  the pressurizing calibration table  64 P is constructed as follows. The air cylinder  20  is initially set to a low pressure in process  142 . This is accomplished by opening the second valve  48  and closing the first valve  44  (or maintaining the first valve  44  in the closed state) for a time period sufficient to exhaust the air cylinder  20  to a low pressure, or until a selected low pressure is reached, followed by pneumatically isolating the air cylinder  20  by closing the second valve  48  while maintaining the first valve  44  in the closed state.  
         [0040]    A first shutoff pressure is selected  144 . This selected shutoff pressure should be greater than the initial low pressure setting of the process operation  142 . The pressurized air supply  46  is connected to the air cylinder  20  in process operation  146  by opening the first valve  44  and maintaining the second valve  48  in the closed state. The pressure sensor  52  is monitored  150  to detect when the instantaneous pressure corresponds to the shutoff pressure, at which point the pressurized air supply  46  is disconnected  152  from the air cylinder  20  by closing the first valve  44  while maintaining the second valve  48  in the closed state. With both valves  44 ,  48  closed, the air pressure regulator  42  is in the isolation state, and the air cylinder  20  is pneumatically isolated.  
         [0041]    The method  140  then pauses  156  for a preselected settling delay time to allow the air cylinder  20  to settle to a steady state pressure. After the preselected delay  156 , the pressure sensor  52  is read to determine the steady state pressure corresponding to the shutoff pressure, and the pressurizing calibration table  64 P is updated  160  to indicate correspondence between the measured steady state pressure and the shutoff pressure. The process operations  144 ,  146 ,  150 ,  152 ,  156 ,  160  are repeated  162  for several increasing shutoff pressures to complete the pressurizing calibration table  64 P.  
         [0042]    With continuing reference to FIG. 1 and with further reference to FIG. 3B, in a preferred method  170  the exhausting calibration table  64 E is constructed as follows. The air cylinder  20  is initially set to a high pressure in process  172 . This is accomplished by opening the first valve  44  and closing the second valve  48  (or maintaining the second valve  48  in the closed state) until a selected high pressure is reached, followed by placing the air pressure regulator  42  into the isolation state by closing the first valve  44  while maintaining the second valve  48  in the closed state.  
         [0043]    A first shutoff pressure is selected  174 . This selected shutoff pressure should be lower than the initial high pressure setting of the process operation  172 . The exhaust pathway  50  is connected to the cylinder in process operation  176  by opening the second valve  48  and maintaining the first valve  44  in the closed state. The pressure sensor  52  is monitored  180  to detect when the instantaneous pressure corresponds to the shutoff pressure, at which point the exhaust pathway  50  is disconnected  182  from the air cylinder  20  by closing the second valve  48  while maintaining the first valve  44  in the closed state. With both valves  44 ,  48  closed, the air pressure regulator  42  is in the isolation state, and the air cylinder  20  is pneumatically isolated.  
         [0044]    The method  170  then pauses  186  for a preselected settling delay time to allow the air cylinder  20  to settle to a steady state pressure. After the preselected delay  186 , the pressure sensor  52  is read to determine the steady state pressure corresponding to the shutoff pressure, and the exhaust calibration table  64 E is updated  190  to indicate correspondence between the measured steady state pressure and the shutoff pressure. The process operations  174 ,  176 ,  180 ,  182 ,  186 ,  190  are repeated  192  for several decreasing shutoff pressures to complete the pressurizing calibration table  64 E.  
         [0045]    In employing the described calibration table construction methods  140 ,  170  for pressurizing and exhausting, respectively, it is recognized that hysteresis may cause the pressurizing characteristics of the air cylinder  20  to be substantially different from the exhausting characteristics. However, for certain air cylinders the air cylinder response may be even more state-dependent. For example, a transition from one-quarter of full pressure to half of full pressure may have a different transient response compared with a transition from substantially fully exhausted to half of full pressure. The calibration table  64  optionally includes additional correspondence data to account for such state-dependent characteristics.  
         [0046]    Moreover, the calibrations  140 ,  170  may need to be repeated occasionally. In one embodiment, it is contemplated to perform the calibration methods  140 ,  170  at the installation of the air cylinder  20 , and also after major maintenance to the air cylinder  20 , damper  14 , or other related components. Recalibration is also preferably performed after replacement of the damper  14 , or after a substantial change in a rate of air flow through the duct  12 . Optionally, the calibration table  64  is updated more frequently using an automated update method, as described next.  
         [0047]    With continuing reference to FIGS. 1 and 2, and with further reference to FIG. 3C, a suitable method  200  for automatically updating the calibration table  64  each time a setting of the damper  14  is changed is described. The method  200  is preferably performed after the initial calibrations  140 ,  170  are performed to initialize the calibration table  64 . In the method  200 , each time a damper setting is changed in accordance with the method  100 , the processor  60  waits  202  a preselected settling period after the air cylinder  20  is isolated  122  in order to allow the air cylinder  20  to reach a steady state. After the delay  202 , the pressure sensor  52  is read to ascertain the steady state pressure, which is used to influence the initial calibration table values to gradually improve accuracy. The pressure is recorded  204  as corresponding to the shutoff pressure used in the method  100 .  
         [0048]    The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.