Abstract:
An actuator is operated to move a mechanical device between two extreme positions of travel. While that motion is occurring, the system quantifies the amount of movement that occurs between those positions. The quantification may involve counting the number of steps of a stepper motor. The number of steps may be used directly as a quantification. Alternatively, the number of steps can be multiplied by the time period of each step to derive the time of the movement between the extreme positions. In addition to being used to setup the actuator upon installation, this automatic ranging method can be performed periodically to compensate for effects of wear on the mechanical device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electrical actuators for operating a mechanical device, such as valves and dampers; and more particularly to techniques for automatically determining the range of travel for the device. 
     Many types of mechanical devices are operated by an electrical actuator which moves components of the device between two extreme positions. For example, the damper in a heating, ventilation and air conditioning (HVAC) system may employ an electric motor to move the damper plate between fully opened and fully closed positions. In other mechanical systems, an electric motor opens and closes a valve to control the flow of a liquid. It may also be desirable in some applications to place the damper or the valve at various positions between fully open and fully closed to provide a variable flow of air or liquid. 
     The mechanical linkage of different types of valves and HVAC dampers require different amounts of rotation to move them between the fully opened and fully closed positions. For example, the mechanical configuration of some HVAC dampers require only 45° of movement to move the damper between those extreme positions, while other dampers require 60° or 90° of movement. Universal actuators are available which rotate their output coupling a maximum of 95°, thus being able to accommodate several types of dampers. Employing a universal actuator eliminates having to stock a variety of actuators specifically designed for each type of mechanical device being driven. However, in order to properly operate a particular damper, the HVAC controller must be configured with the amount of travel or movement that the actuator has to provide to move the mechanical device between its extreme positions. That configuration also enables the controller accurately to place the damper at various desired intermediate positions. 
     Previously the controller was configured manually with the appropriate amount of rotational movement required by the associated damper. Such manual configuration was time consuming and prone to human error. In addition, the controller had to be reconfigured periodically to compensate for wear of the mechanical device. 
     SUMMARY OF THE INVENTION 
     A general object of the present invention is to provide a method by which a controller for an electromechanical actuator can automatically determine the range of movement for a particular mechanical device to which the actuator is connected. 
     Another object is to provide such an auto ranging mechanism that is periodically recalibrated to compensate for the effects of wear on the mechanical device. 
     These and other objectives are satisfied by a method which commences by placing the mechanical device into the one of the extreme positions of its range of movement. Then the actuator is energized to move the mechanical device into the other extreme position. 
     While the device is moving, the amount of movement which occurs for the mechanical device to reach the second extreme position from the first extreme position is quantified. That amount of movement can be quantified by any of several measurement parameters. For example, the time of movement may be measured, or when a stepper motor is used, the number of steps can indicate the range of movement. The time of movement may be derived indirectly by the number of steps multiplied by the period of each one to derive the time of the movement between the extreme positions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a damper with an actuator connected thereto; 
     FIG. 2 is a block schematic diagram of the actuator and a controller; and 
     FIG. 3 is a flow chart of an auto ranging routine which is executed by the controller within the actuator. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With initial reference to FIG. 1, a mechanical device such as a VAV box  10  for a HVAC system has a circular duct  12  with a circular plate  14  which is mounted within the duct on shaft  16 . By rotating the shaft  16 , the plate  14  can be pivoted 90° between fully opened and fully closed positions. The damper plate  14  strikes a first stop  18  when in the fully closed position and strikes a second stop  19  in the fully opened position. The damper plate  14  also may assume an infinite number of orientations between the fully opened and fully closed positions. 
     The shaft  16  for damper plate  14  extends through an aperture of the side wall of the duct  12  where it is engaged by an actuator  20 . Actuator  20  receives a command from a controller  21  for the HVAC system which directs the actuator to move the damper plate  14  into a given position. The given position may be fully opened, fully closed, or any one of a number of positions therebetween. The actuator  20  responds to the command signal by rotating the damper shaft until the desired position is achieved. The command signal indicates a percentage that the damper is to be opened and the controller  21  then determines from that percentage command how much to rotate the damper rod and plate. 
     With reference to FIG. 2, the actuator  20  comprises a stepper motor  22  which is connected to drive the damper shaft  16 . In point of fact, the damper motor may be connected by a reduction gear assembly to the damper shaft  16  so that many revolutions of the motor are required to rotate that shaft 90° between the fully opened and fully closed positions of the damper. For example, in a typical embodiment of the present invention 23,000 steps of the stepper motor  22  may be required to rotate the motor 95° which is the maximum amount of its travel. Thus the 95° motion produced by the actuator  20  can accommodate mechanical devices such as VAV box damper plate  14  which have extreme limits of travel between 0° and 90°. The motor  22  is stepped by electrically pulses received from a conventional motor drive circuit  24  which is operated by a microcontroller  26 . The microcontroller responds to commands received on communication network  28  from the HVAC controller for the building zone in which the VAV box  10  is located or from feedback received from a velocity pressure sensor as in variable air volume applications. 
     With continuing reference to FIGS. 1 and 2, the damper shaft  16  extends through the actuator  20  where a motion sensor  30  is mounted to produce a signal indicative of shaft movement. This motion sensor  30  may be mounted on the damper shaft  16  or on any of the gear passes within the actuator  20 . For example, the motion sensor  30  may be a Hall effect type or an optical type device which emits electrical pulses periodically while the shaft  16  is moving. The pulsed output signal from the motion sensor  30  is applied as an input to the microcontroller  26  so that the microcontroller is able to detect whether the shaft is in motion. Alternatively, certain motors produce an increase in current when the shaft stops rotating. Such current increase can be detected by the controller. As will be described, when the damper plate  14  abuts one of the stops  18  or  19  in an extreme position of rotation, the motor  22  stalls which is indicated by the cessation of electrical pulses from the motion sensor  30  or a current increase from the motor. 
     Although the present VAV box damper plate  14  is rotated 90° between the fully opened and fully closed positions, other dampers may have different degrees of movement between those extreme positions. It is not uncommon for dampers to rotate 45° or 60° between those extreme positions. As a consequence, the microcontroller  26  must know the range of rotation between the extreme positions of the particular damper on which it is mounted. Otherwise electrical pulses may continue to be applied to the stepper motor after the damper abuts a stop, which could adversely affect the motor  22  or bend the damper stops  18  and  19 . 
     Therefore, whenever the actuator  20  is powered up, the microcontroller  26  executes a routine stored within its internal memory that determines the range of movement between the fully opened and fully closed positions of the damper. Thus the microcontroller automatically learns the full range of movement for the particular mechanical device to which the actuator is attached. That information is useful in determining how to operate the motor in order to move the damper to fully open and fully closed positions, as well as various commanded positions therebetween. In addition to being executed whenever power is initially applied to the actuator  20 , the automatic ranging routine may also be executed periodically (e.g. once a month) to account for slippage of the damper plate  14  on the shaft  16  and for worn damper seals. Whenever it is executed, the automatic ranging routine may provide the results as diagnostic signals to a facility management system for the building, for example. 
     Upon commencement of the automatic ranging routine depicted in FIG. 3, the microcontroller  26  starts a software timer at step  40  with a known value. If the routine has not been executed before, that value corresponds to the time period required for the actuator to move its 95° maximum travel. This 95° value is slightly greater than the 90° travel necessary to move the damper plate  14  between its extreme travel positions to account for poorly positioned end stops  18  and  19 . Once started the timer begins decrementing the known value. 
     Then the program execution advances to step  42  at which the microcontroller issues a sequence of signals to the motor drive  24  which causes the motor  22  to step toward the open position of the VAV box damper plate  14 . At step  44  the microcontroller  26  inspects its internal timer to determine whether the timer period has elapsed. If it has, this would be an indication that the shaft is slipping. If so, the microcontroller sets a failure flag at step  46  and a failure message is sent over the communication network  28  to a central monitoring station at step  47  before the automatic ranging routine terminates. However, on most occasions the timer will not have timed-out at step  44  and the program execution will advance to step  48 . At that juncture, the microcontroller  26  checks the signals from the motion sensor  30  to determine whether the motor  22  still is operating. The program execution continuously loops through steps  44  and  48  until either the time-out or a motor stall occurs. 
     Eventually the microcontroller  26  will no longer detect pulses being emitted by the motion sensor  30 , indicative that the motor has stalled due to the damper plate  14  striking the second stop  19  in the fully open position. The automatic ranging routine then advances to step  50  where a variable designated FULL STROKE STEPS is set to zero. Then the software timer is reset at step  52  by the microcontroller  26  to the same value as before. 
     Next the microcontroller sends signals to the motor drive  24  which cause the motor  22  to step in the opposite direction moving the damper plate  14  to the fully closed position. While this is occurring, the program execution loops through steps  56  and  58  where the microcontroller  26  checks for a timer time-out or a motor stall, respectively. If at step  56  the time-out is detected the failure flag is set at step  60  and a failure message is sent over the communication network  28  to a central monitoring station at step  61  before the automatic ranging routine terminates. Termination of the automatic ranging routine with the failure flag set indicates that the procedure failed to execute properly and has not provided the proper output variables, as will be described. 
     When a motor stall is detected at step  58 , the damper plate  14  is likely to have reached the fully closed position at which it abuts the first stop  18 . Upon this detection the program execution branches to step  62  where the FULL STROKE STEPS variable is set equal to the number of electrical pulses which drove the motor  22  between the fully opened and fully closed positions. This number of motor pulses indicates the rotational distance that the damper plate  14  moved between those extreme positions. At step  64 , the time which was required for that motion of the damper plate is computed by multiplying the number of FULL STROKE STEPS by the time per motor step. The resultant value designated ACTUATOR TIME is stored within the memory of the microcontroller  26  and the automatic ranging routine terminates. 
     At the culmination of the automatic ranging routine, the memory of the microcontroller  26  stores the amount of motion of the damper between its extreme positions in terms of the number of stepper motor steps and the time of motion. Either of those values then can be utilized to properly control the stepper motor  22 . For example, when the microcontroller  26  receives a command to move the damper plate from one extreme position to the other, either the number of stroke steps required or the actuator time can be employed to ensure that full motion of the damper plate occurs without continuing to drive the motor  22  after the damper plate has struck one of the stops  18  or  19 . In addition, when the microcontroller  26  receives a command on communication network  28  to move the damper plate to an intermediate position, for example thirty percent from fully closed to fully opened the microcomputer can determine that position in terms of either movement time or motor steps. This is accomplished by multiplying the desired position, e.g. thirty percent, by the number of FULL STROKE STEPS or the ACTUATOR TIME. 
     The present invention provides a mechanism by which an actuator  20  automatically determines the amount of movement of the driven mechanical mechanism, such as the VAV box damper plate  14 , between the extreme positions of that device&#39;s motion. As a consequence, when the system is first installed, the technician need not manually designate that amount of movement. In addition when drift or other changes in the operation of the mechanical device occur over time, periodic execution of the automatic ranging routine ensures that the actuator will properly operate the device. 
     This method also can be applied to fluid valves, such as water or steam valves in HVAC applications. Precise control of flow can be achieved along with detection of worn valve seats or stuck valves.