Patent Publication Number: US-2005122096-A1

Title: Detector for sensing the rotational movement of an electric motor in stand-by mode

Description:
TECHNICAL FIELD  
      This invention relates to motor-driven household appliances, especially to a detector for sensing the rotational movement of its electric motor in stand-by mode.  
     BACKGROUND OF THE INVENTION  
      In the existing motor-driven household appliances, no detector is provided to indicate whether they are normal in stand-by mode (when the power is on but the machines are not initiated yet). Therefore, if abnormality occurs, users will likely be hurt when the machines are initiated, especially for those with blade or blade disc.  
     SUMMARY OF THE INVENTION  
      The main object of the present invention is to overcome the shortcomings of the prior art and to provide a detector to sense the rotational movement of an electric motor in stand-by mode.  
      The detector according to the present invention comprising: 
          a control circuit,     a thyristor,     and a power supply circuit;     wherein, one output terminal of said control circuit is connected to the gate of said thyristor, and wherein said power supply circuit, electric motor and thyristor are connected in series; wherein said detector further includes a sensing circuit and an indicator light, said sensing circuit for detecting whether the loop of said power supply circuit, electric motor and thyristor are conducting; wherein one output terminal of said sensing circuit is connected to said control circuit for providing a feed-back signal to said control circuit; wherein said control circuit has an output terminal connected to said indicator light so as to control an on/off state of the indicator light.        

      Said power supply circuit may be an alternating power source, and said thyristor may be a triac.  
      Said sensing circuit may include a Hall sensor, which is suitably positioned to sense the rotational movement of said electric motor.  
      Said sensing circuit may include a photodiode. If the thyristor is a triac, the sensing terminals of said sensing circuit may be connected respectively with T 1  terminal and T 2  terminal of said triac. If the thyristor is a scr, the sensing terminals of said sensing circuit may be connected respectively with the anode and cathode of said scr.  
      Said sensing circuit may include a mutual inductance, the primary circuit of said inductance is connected between said triac and electric motor, the secondary circuit of said inductance is for providing feed-back signals to said control circuit.  
      The working principle of said detector is as follows:  
      In normal stand-by mode, the loop of said power supply circuit, electric motor and thyristor is non-conducting. If no rotational movement of the electric motor is detected or if the thyristor is detected to be non-conducting, it means that the machine is in normal status, then the indicator light flashes under the control of the control circuit, so as to indicate permit of further operations to the machine. If rotational movement of the electric motor is detected or if the thyristor is detected to be conducting, it means that the machine is in abnormal status, then the indicator light is off under the control of the control circuit, so as to indicate abnormality and prohibition of any further operations to the machine.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is the schematic circuit block diagram of the first embodiment of the present invention, wherein, the sensing circuit using a Hall sensor;  
       FIG. 2  is the schematic circuit block diagram of the second embodiment of the present invention, wherein, the sensing circuit is connected across the thyristor;  
       FIG. 3  is the schematic circuit block diagram of the third embodiment of the present invention, wherein, the sensing circuit is connected across the electric motor;  
       FIG. 4  is the schematic circuit block diagram of the fourth embodiment of the present invention;  
       FIG. 5  is the circuit connect diagram of the detector shown in  FIG. 1 ;  
       FIG. 6  is the circuit connect diagram of the detector shown in  FIG. 2 ;  
       FIG. 7  is the circuit connect diagram of the detector shown in  FIG. 3 ;  
       FIG. 8  is the circuit connect diagram of the detector shown in  FIG. 4 ;  
       FIG. 9  is a circuit connect diagram showing an alternative circuit of the indicator light according to the present invention;  
       FIG. 10  is a circuit connect diagram showing an alternative circuit of the control circuit according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
      As shown in  FIG. 1 , in the first embodiment, the detector comprises a control circuit B, a thyristor C, an electric motor D, a power supply circuit A, a sensing circuit F and an indicator light E.  
      The sensing circuit F may use a Hall sensor, which is suitably positioned to detect the rotational movement of the electric motor D.  
      One output terminal of the sensing circuit F is connected to the control circuit B and sends feed-back signals to the control circuit B. The control circuit B has an output terminal connected to the indicator light E so as to control the on/off of the indicator light E.  
      As shown in  FIG. 5 , the power supply circuit A is supplying an alternating current, the thyristor C is a triac, and the indicator light E is a red LED light. If the motor D is not rotating, the magnetic field of the motor D will not change, then, the sensing circuit F will not be initiated, and the leg  3  of the sensing circuit F will keep sending a high level voltage signal to the control circuit B. After judgement, the control circuit B sends a voltage signal, the level of which is alternating in a certain pattern, to the LED light E. When the voltage signal sent from the control circuit B is at high level, the LED light E is on, while when the voltage signal sent from the control circuit B is at low level, the LED light E is off, so that, the LED light flashes. If the motor D is rotating, the sensing circuit F will be initiated by the changing magnetic field of the motor D, then, the leg  2  and leg  1  of the sensing circuit F will be conducting, and the leg  3  of the sensing circuit F will input a low level voltage signal to the control circuit B. After judgement, the control circuit B sends a low level voltage signal to the LED light E and the LED light E is off.  
     Embodiment 2  
      As shown in  FIG. 2 , the difference from embodiment 1 is that, the sensing circuit F is using a photodiode, the two terminals of the sensing circuit F is connected respectively with the terminal T 1  and terminal T 2  of the triac C. If the terminals T 1  and T 2  are conducting, no current flow is in the sensing circuit F, the sensing circuit F then sends feed-back signals to the control circuit B, the red indicator light E will be off under the control of the control circuit B. If the terminals T 1  and T 2  are non-conducting, there is current flow in the sensing circuit F, the sensing circuit F then sends feed-back signals to the control circuit B, the red indicator light E will flash under the control of the control circuit B.  
      As shown in  FIG. 6 , If the terminals T 1  and T 2  of the triac are conducting, there is no current flow between the leg  3  and leg  2  of the sensing circuit F, and the photodiode will be non-conducting, the leg  1  of the sensing circuit F keeps sending a high level voltage to the control circuit B. After judgement, the control circuit B sends a low level voltage signal to the LED light E and the LED light E is off. If the terminals T 1  and T 2  of the triac are non-conducting, there is current flow between the leg  3  and leg  2  of the sensing circuit F, and the photodiode will be conducting, the leg  3  of the sensing circuit F will input a low level voltage signal to the control circuit B. After judgement, the control circuit B sends a voltage signal, the level of which is alternating in a certain pattern, to the LED light E to make it flash.  
     Embodiment 3  
      As shown in  FIG. 3 , the difference from embodiment 1 is that, the sensing circuit F is using a photodiode, the two sensing points are connected respectively with the two terminals of the motor D. If there is current flow in the loops of the motor, there will be current flow in the sensing circuit F, the sensing circuit F then sends feed-back signals to the control circuit B, the red indicator light E will be off under the control of the control circuit B. If there is no current flow in the loops of the motor, there will be no current flow in the sensing circuit F, the sensing circuit F then sends feed-back signals to the control circuit B, the red indicator light E will flash under the control of the control circuit B.  
      As shown in  FIG. 7 , If there is current flow in the loops of the motor, there will be current flow between the leg  3  and leg  2  of the sensing circuit F, and the photodiode will be conducting, the leg  3  of the sensing circuit F will input a low level voltage signal to the control circuit B. After judgement, the control circuit B sends a low level voltage signal to the LED light E and the LED light E is off. If there is no current flow in the loops of the motor, there will be no current flow between the leg  3  and leg  2  of the sensing circuit F, and the photodiode will be non-conducting. The leg  1  of the sensing circuit F keeps sending a high level voltage to the control circuit B. After judgement, the control circuit B sends a voltage signal, the level of which is alternating in a certain pattern, to the LED light E to make it flash.  
      For either of embodiments 2 and 3:  
      The sensing circuit F may be in an alternative circuit as shown in  FIG. 10 , wherein one diode is replaced by four diodes.  
      The photodiode may be chosen from 817 series or other series. The diodes may be chosen from series 1N4001-4007.  
     Embodiment 4  
      As shown in  FIG. 4  and  FIG. 8 , the difference from embodiment 1 is that, the sensing circuit F is using a mutual inductance G, the primary circuit of the inductance G is connected between the triac C and the electric motor D, the secondary circuit of the inductance G sends feed-back signals to the control circuit B. If there is current flow in the primary circuit of the inductance G, then there will be current flow as well as voltage in the secondary circuit of the inductance G, the sensing circuit F then inputs a low level voltage signal to the control circuit B. After judgement, the control circuit B sends a low level voltage signal to the LED light E and the LED light E is off. If there is no current flow in the in the primary circuit of the inductance G, then there will be no current flow in the in the secondary circuit of the inductance G, the sensing circuit F keeps sending a high level voltage to the control circuit B. After judgement, the control circuit B sends a voltage signal, the level of which is alternating in a certain pattern, to the LED light E to make it flash.  
      For any of embodiments 1, 2, 3 and 4:  
      The light E may be connected with the control circuit B in an alternative way as shown in  FIG. 9 . When the control circuit B sends out a low level voltage, the light E is on, while when the control circuit B sends out a high level voltage, the light E is off.