Patent Publication Number: US-2004057553-A1

Title: Fan control circuit for x-ray tube device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Technical Field  
       [0002] The present application relates generally to imaging systems, and more particularly, to imaging systems that use a fan as part of the cooling system.  
       [0003] 2. Background  
       [0004] Various types of imaging such as CT systems use a cooling system to cool the X-ray tube. The cooling system typically employs a liquid-to-air heat exchanger to remove heat from the X-ray tube during operation. The liquid cooler typically includes a fan that is used to remove heat to the ambient air. Heat exchangers are sized for the maximum steady state capable of the X-ray tube. Many X-ray systems operate at a much lower average power for which the heat exchanger is designed. The fans of such system run at a very high speed. This high speed is much higher than necessary to remove the heat generated by the X-ray tube. Such fans are noisy and have been found to be disturbing to both patients and radiologists.  
       [0005] It would therefore be desirable to reduce the amount of noise during operation of an X-ray system.  
       SUMMARY OF INVENTION  
       [0006] In one aspect of the invention the X-ray system comprises an X-ray tube temperature sensor generating a temperature signal and a fan coupled to the temperature sensor. The fan has a speed that varies in response to the temperature signal.  
       [0007] In a further aspect of the invention, a method for operating an X-ray system comprises measuring a temperature of an X-ray tube and controlling the fan speed in response to the temperature.  
       [0008] One advantage of the invention is that patient comfort is increased due to the fan operating at lower speeds when the temperatures are lower. Typically the temperatures increase slowly and thus the fan speed slowly increases which makes the corresponding increase in noise less noticeable.  
       [0009] Other aspects and advantages of the present invention will become apparent upon the following detailed description and appended claims, and upon reference to the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0010]FIG. 1 is a block diagrammatic schematic view of an X-ray system having a fan control circuit according to the present invention.  
     [0011]FIG. 2 is a plot of fan speed with sound levels versus temperature for the system according to the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0012] The present invention is described with respect to a CT type system. Those skilled in the art will recognize that the present invention is also applicable to various types of X-ray systems.  
     [0013] Referring now to FIG. 1, an X-ray system  10  such as a CT system is illustrated. The CT system illustrated is simplified to highlight the aspects of the present invention. Those skilled in the art will recognize various other components are present in such systems. CT system  10  includes a controller  12 . Controller  12  is preferably microprocessor-based. Controller  12  may be a single central controller or may be a controller specifically designed to control the operation of a cooling system  14  for an X-ray tube  16 . X-ray tube  16  is thermally coupled to a heat exchanger  18 . Heat exchanger  18  may be a liquid-to-air type heat exchanger typically used in X-ray systems. Heat exchanger  18  may have an integral fan or fans  20  coupled thereto. Those skilled in the art will recognize that fan  20  may also be a separate component placed adjacent to heat exchanger  18 . Fan  20  is designed to help move air over the heat exchanger to cool the heat exchanger  18  and ultimately X-ray tube  16 . Controller  12  is operably coupled to fan  20  to control the speed thereof.  
     [0014] Heat exchanger  18  may also include a thermistor  22 . Thermistor  22  may actually be an integral component with heat exchanger  18 . Thermistor  22  generates a temperature signal corresponding to the amount of temperature present in the heat exchanger. Thermistor  22  is coupled to a voltage source  30 . Thus, the voltage change across thermistor  22  from voltage source  30  changes in response to the temperature of the heat exchanger  18 . A shape resistor  32  may be positioned electrically in parallel with thermistor  22 . Resistor  32  may be referred to as a shape resistor. A shunt  34  may also be positioned in parallel with the thermistor  22  and resistor  32 . Thus, each of the thermistor  22 , resistor  32 , and shunt  34  have two common nodes N 1  and N 2 . Shunt  34  is thermally controlled to close when a high temperature is sensed. That is, at temperatures above 100° C., shunt  34  may be closed. Otherwise, shunt  34  is normally open.  
     [0015] In series with the parallel combination of thermistor  22 , resistor  32 , and shunt  34 , a gain resistor  36  may also be coupled to node N 2 . Shape resistor provides a voltage divider so that controller has a proper range of controlling voltage thereto. Node N 2  is coupled to controller  12  to monitor the temperature signal from thermistor. Based upon the output of the temperature signal, controller  12  controls the speed of fan  20 . The speed of the fan preferably varies over the temperature range except when the temperature reaches the shunt closing temperature. Also, to prevent the fan from not operating when the X-ray tube is cold, a pair of diodes  38  and  40  may be provided so that the controller constantly has some voltage and operates the fan at a minimal speed. As shown, the series connection of diodes  38  and  40  has the anode of diode  38  coupled to the gain resistor while the cathode of diode  38  is coupled to the anode of diode  40 . The cathode of diode  40  is coupled to ground.  
     [0016] In addition, an over temperature switch  42  and an over pressure switch  44  may also be coupled to voltage source  30 . Thus, if the temperature of X-ray tube  16  exceeds a certain pressure or temperature, the signal is received by controller  12 . Controller  12  may also control the fan to the maximum fan speed upon the sensing of high temperature or pressure within the X-ray tube  16 .  
     [0017] In operation, thermistor  22  generates a temperature signal responsive to the temperature within the heat exchanger  18  which directly corresponds to the temperature in X-ray tube  16 . The fan speed changes in response to the temperature signal until a maximum fan speed is reached.  
     [0018] Referring now to FIG. 2, as the temperature within the heat exchanger increases the temperature signal also changes from the thermistor  22 . Thus, FIG. 2 illustrates the fan speed that changes in response to the temperature. When a predetermined temperature such as 100° is reached, the fan speed is elevated to maintain a maximum fan speed. As illustrated, the maximum fan speed is about 2900 rpm. As can be seen, the output of the controller and thus the operation of the fan is non-linear. Sound level measurements are also provided for various speeds. As speed increases sound level increases.  
     [0019] While the invention has been described in connection with one or more embodiments, it should be understood that the invention is not limited to those embodiments. On the contrary, the invention is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the appended claims.