Patent Publication Number: US-2003223877-A1

Title: Blower assembly with closed-loop feedback

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to the art of blower assemblies and more particularly a blower assembly that generates a constant pressure value. Specifically, the present invention relates to a blower assembly which monitors at least one pressure transducer for generating a pressure signal that is used by a controlling circuit coupled to the motor to adjust the motor speed to obtain the desired constant pressure value.  
       BACKGROUND OF THE INVENTION  
       [0002] It is known to use blowers in many different applications from vacuum cleaners to furnaces and other industrial applications. Blowers may also be used in critical applications such as medical equipment where the generation of a constant pressure is very important.  
       [0003] Blower assemblies are housings which carry a motorized fan. The housing has an inlet which allows for the drawing in of ambient air which is redirected by the fan through an exhaust outlet. One use for a blower in a medical application is for patients who have sleep apnea. In such a condition, the sleeping patient unknowingly ceases to breathe and in severe cases can suffocate one&#39;s self. In order to prevent this, a blower is used in an assisted-breathing apparatus to help regulate the breathing of the patient so as to preclude cessation of respiration.  
       [0004] Prior blower assemblies used in medical applications used a velocity feed-back loop to assist in the patient&#39;s breathing. Such a system monitored the velocity of the air expelled by the fan assembly and the velocity data was then used to regulate the motor speed. However, such a system characteristic—exhaust velocity—has been found to be inaccurate and unable to meet the system requirements for critical medical applications. In particular, the exhaust velocity values are not nearly as accurate as monitoring the pressure which is believed to be the critical variable in such applications.  
       [0005] Based upon the foregoing, there is a need in the art for a closed loop pressure blower that utilizes a pressure reading to generate the necessary information for controlling the speed of the motor.  
       DISCLOSURE OF THE INVENTION  
       [0006] In light of the foregoing, it is a first aspect of the present invention to provide blower assembly with closed-loop feedback. The aspects of the invention which shall become apparent as the detailed description proceeds are achieved by a blower assembly having a motorized fan that draws ambient air in through an inlet and exhausts air out an outlet; a control circuit coupled to the motorized fan; a pressure sensing device near the outlet to measure pressure of the exhaust air and generating a pressure signal; and the control circuit receiving the pressure signal and adjusting the speed of the motorized fan to obtain a desired pressure at the outlet.  
       [0007] Another aspect of the invention which will become apparent herein is obtained by A method for generating a desired pressure value from a blower assembly that includes a motorized fan that draws in ambient air through an inlet and exhausts air out an outlet, the method comprising: inputting a set pressure value to a control circuit; positioning a pressure sensing device near the outlet generating a pressure signal by the pressure sensing device; receiving said pressure signal in said control circuit; and adjusting the speed of the motorized fan by said control circuit depending upon the value of said pressure signal to match said set pressure value. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] For a complete understanding of the objects, techniques, and structure of the invention, reference should be made to the following detailed description and the accompanying drawings wherein:  
     [0009]FIG. 1 is an elevational view, in partial cross-section, of a blower assembly according to the present invention;  
     [0010]FIG. 2 is a plan view of the blower assembly interfaced with a flow tube;  
     [0011]FIG. 3 is a schematic diagram of the blower assembly according to the present invention;  
     [0012]FIG. 4 is a flow chart setting forth the control steps of the blower assembly according to the present invention; and  
     [0013]FIG. 5 is a flow chart for setting flow variation of the operational steps for the blower assembly according to the present invention.  
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0014] Referring now to the drawings and more particularly to FIGS. 1 and 2. It can be seen that a closed-loop blower assembly utilizing pressure feedback is designated generally by the numeral  10 . The blower assembly  10  includes a housing  12  which may be of a split construction that is assembled around the components of the blower assembly. The split housing may be secured by snap-type fasteners, by threaded fasteners or the like. The blower assembly  10  includes a motor  14  which as shown in the present drawing is a brushless DC motor. However, it should be appreciated that other types of motors could be used in the present invention. Such motors include, but are not limited to, AC induction, switched reluctance or universal brush type motors. It will be appreciated that although a blower configuration is shown, it is well within the scope of the present invention that the aspects taught herein are equally applicable to a pump configuration. In any event, the motor  14  drives or rotates a shaft  16  which in turn rotates a fan  20 . The fan has an inlet  22  and a plurality of vanes  24 . The housing  12  provides an opening  26  aligned with the inlet  22  for drawing in ambient air which is then exhausted by the fan  20  through an exhaust port  28 . Although only a single port  28  is shown, it will be appreciated that multiple ports could be provided.  
     [0015] A control circuit board assembly  30  is secured within the housing  12  and in the present instance functions as a mounting board for the motor  14 . The control circuit board  30  provides a power connector  32  which allows the blower assembly to receive and distribute power as required and also to receive and output data needed for operation of the blower assembly  10 .  
     [0016] Referring now to FIG. 3, it can be seen that a schematic diagram of the blower assembly  10  is presented. As noted previously, the motor  14  and the fan  16  are associated with a control circuit board  30 . The control circuit  30  includes a controller  40 . The controller  40  provides the necessary hardware, software and memory for controlling the operation of the motor  14  and thus the blower assembly  10 . The controller  40  may be a programmable micro-controller, a digital signal processor, or a custom integrated circuit specifically designed to regulate motor speed. In particular, the custom integrated circuit may be an application specific integrated circuit or a field programmable gate array. Any of the foregoing devices may be programmed to react in a manner as required by each end-use application. Accordingly, although the present invention is directed to maintaining a specified pressure of air that is exhausted from the blower assembly, it will be appreciated that the range of pressures or a rate of pressure increase or decrease could be generated by the present invention. As such, these custom programs may allow for endless iterations for direct customization by application.  
     [0017] In order to obtain the particular control features of the present invention, a pressure transducer  42  is positioned in the housing  12  in close proximity to the exhaust port  28 . The pressure transducer may be a differential, absolute, or gauge pressure transducer that generates an electrical output signal that is received by the controller  40 . Also providing input to the controller  40 , may be a thermistor  44  which is coupled to the motor  14  or related component. The thermistor  44  may detect ambient air temperature or the temperature of temperature-critical components that may adversely affect the pressure reading taken by the pressure transducer  42 . The temperature reading is input to the controller  40  to make any necessary adjustments. At least one Hall effect switch  46  may be coupled to the motor to detect the speed thereof. This speed information is input to the controller  40  to provide the necessary information for the speed of the motor at any given moment. In the preferred embodiment, a set of three Hall effect switches  46  are used to accurately determine rotor position for proper commutation.  
     [0018] A second pressure transducer  48  may be placed in a flow tube  49  that is coupled to the exhaust port  28 . The flow tube  49  is associated with the end-use device coupled to the blower assembly. Or the transducer  48  may be placed in any other desired location so as to obtain a pressure differential reading. In other words, the information generated by the second pressure transducer is compared to the information generated by the first pressure transducer  42  by the controller to adjust the speed of the motor  14  accordingly. Data collected by the transducer  48  is transferred by a signal wire or conduit  51  to the controller  40 .  
     [0019] It will also be appreciated by one skilled in the art that an input device  50  may allow for an end-user to establish a particular operating pressure set point for the piece of equipment to be associated with the blower assembly. This input can include a single set point or a range of operating points to allow for efficient operation of the motor of the equipment. The input device  50  may transfer data to the controller  40  via the power connector  32  or other similar connection device.  
     [0020] Referring now to FIG. 4 of the drawings an operational flow chart employed by the controller  40  is designated generally by the numeral  100 . At a first step  102 , pressure from the external pressure transducer  42  is measured and this information is converted to an electrical signal at step  104 .  
     [0021] At step  106 , a desired pressure input may be provided by the control input device  50  or by a factory-set value programmed into the controller  40 . Additional information which is supplied to the controller  40  is indicated at step  108  wherein a temperature may be detected by the thermistor  44  at the power supply, ambient or other internal control temperature. At step  110 , the measured temperature is converted to an electrical signal and sent to the controller  40 . Accordingly, at step  112 , based upon the inputs received, the controller  40  determines whether the measured pressure equals the desired pressure, and if required, whether that pressure should be adjusted based upon the temperature detected by the thermistor  44 . In the event that the pressure is to be adjusted based upon the temperature, it will be appreciated that look-up tables contained within the controller&#39;s memory may be utilized to provide an adjustment factor to the pressure value desired. In any event, at step  114 , if the actual pressure is less than the desired pressure, then at step  116  the controller  40  increases the motor speed by increasing the pulse width modulation duty cycle of the power applied to the motor. In a similar fashion, at steps  118  and  120  if the pressure is at the desired level then the duty cycle is not changed at step  120 . Or, at step  122 , if it is determined that the actual pressure is more than the desired pressure then at step  124  the motor speed is decreased by decreasing the duty cycle. At step  126 , the internal motor control adjusts the speed of the motor. Accordingly, at step  128 , the motor controls the speed of the blower assembly or fluid pump, which corresponds to the pressure output. The process then returns to step  102  to repeat the foregoing steps.  
     [0022] Referring now to FIG. 5 a methodology is indicated by the numeral  200  for utilizing the controller  40  and the associated components for the purpose of obtaining a differential pressure value for use with the blower assembly  10 . In particular, at step  202 , a pressure generated by an external source is measured by the pressure transducer  42 . At step  204 , a second reference pressure is measured by the pressure transducer  48 . And then at step  206 , these signals are converted into an appropriate electrical signal and sent to the controller  40 .  
     [0023] Additional information which is input to the controller  40  is indicated at step  208 , wherein a control signal may be input by the device  50  to establish a desired pressure value for the attached equipment. At step  210 , a temperature value may be measured by the thermistor  44  at the appropriate location associated with the assembly  10 . At step  212 , the measured temperature value is converted to an electrical signal and the input and temperature information is submitted to the controller for evaluation at step  214 .  
     [0024] The controller  40  at step  214 , measures the differential pressure, that is the difference between the values read by the pressure transducers  42  and  48 , and compares the difference value, which may be adjusted by the temperature value detected by the thermistor  44 , to the desired differential pressure value. Accordingly, at step  216 , if the actual differential pressure is less than the desired differential pressure, then the controller at step  218  increases the motor speed by increasing the duty cycle. If, the pressure is the same as desired—or within a specified range—at step  220 , then the controller  40  instructs the motor to maintain the normal operating duty cycle at step  222 . If, however, the actual differential pressure is more than desired, at step  224 , then the controller  40  decreases the motor speed at step  226  by decreasing the duty cycle.  
     [0025] At step  228 , the controller  40  adjusts the speed of the motor and in turn the motor controls the speed of the fan or fluid pump at step  230 . Upon completion of step  230 , the controller returns the process step to  202  and the foregoing steps are repeated.  
     [0026] Based upon the foregoing those skilled in the art will appreciate the advantages of the present invention. By utilizing a blower with integrated pressure sensing and feedback, precise control of the blower output performance can be obtained. The control pressure system includes a pressure sensing device or devices which provide electrical output signals to the controller. The controller may be programmed to react to changes in the input signal from the pressure feedback device with appropriate compensation for temperature and other variables. This may be accomplished by the programming code of the controller  40  or by alternating the pulse with modulation duty cycle submitted to the motor until a predetermined pressure, or pressure range is achieved.  
     [0027] In an application which requires a constant pressure source, a restriction or blockage downstream from the blower will cause a positive pressure differential as compared to the speed input command setpoint. In this condition, the controller  40  program forces the blower to slow down or brake, thereby reducing the pressure output to the original setpoint. In this type of application when there is a decrease in restriction, downstream from the blower, a negative pressure differential as compared to the speed input command setpoint would be detected. In this condition, the controller program would cause the blower to accelerate, thereby increasing the pressure output to the original setpoint. From the foregoing, it can be seen that the present invention is advantageous in that the controller coupled with the pressure feedback devices and other monitoring components such as motor speed and temperature can be programmed to react in a manner as required by each individual application. Accordingly, a custom program embedded in the controller allows for endless iterations for direct customization by the end-use application.  
     [0028] Thus, it can be seen that the objects of the invention have been satisfied by the structure and its method for use presented above. While in accordance with the Patent Statutes, only the best mode and preferred embodiment has been presented and described in detail, it is to be understood that the invention is not limited thereto or thereby. Accordingly, for an appreciation of the true scope and breadth of the invention, reference should be made to the following claims.