Abstract:
[Object] To provide an induced signal removing circuit that feeds back induced voltage regarded as electrical signals into the input side of an inductive load to remove the induced voltage from the metal part, the induced voltage appearing even across an insulated metal part in response to signals input to the inductive load. 
     [Solution to Problem] An induced signal removing circuit for removing induced signals generated in a metal part in response to electrical signals input to an inductive load, including: an input terminal connected to the metal part insulated from the inductive load, the input terminal receiving the induced signals; two output terminals connected to an input side of the inductive load, the input side receiving the electrical signals, the output terminals outputting the induced signals received from the input terminal; and a signal flow controller between the input terminal and each output terminal, the controller causing the induced signals to flow in only one direction from the input terminal to either output terminal.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an induced signal removing circuit that feeds back induced voltage in the form of electrical signals into the input signal of an inductive load to remove the induced voltage from the metal part. The induced voltage appears even across an insulated metal part in response to signals input to the inductive load. 
       BACKGROUND ART 
       [0002]    In an electronic or electrical circuit using an inductive load (inductance), signals input to the inductive load generate voltage by electromagnetic induction even across an adjacent metal part insulated from the inductive load. Such induced voltage varies according to signals input to the inductive load. A potential difference caused by induced voltage generates current flow. Such induced current or voltage, which may cause an electric shock, is unnecessary for the operation of the electrical circuit and thus is removed by the grounding method in conventional electrical circuits (see Patent Literature 1, for example). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2010-093593 
       
     
         [0004]    In a conventional grounding method, a metal part where induced voltage may be generated is grounded or connected to a metal part of the housing of the electrical circuit by lead lines, such as a grounding conductor, to have zero potential, i.e., ground potential or the same potential as the housing. With such a method, induced voltage is undetectable with a measuring device and thus is regarded as “removed”. Actually, the grounding method does not completely remove induced voltage from the electrical circuit. Specifically, the grounding method only removes voltage of static electricity. Induced voltage that acts like electrical signals in response to varying input signals is just absorbed by a ripple filter for the power supply or instantaneously discharged through the housing. This reduces the potential difference and makes the induced voltage undetectable with a measuring device. 
         [0005]    In a conventional grounding method, a metal part is electrically charged due to induced voltage. In this state, potential difference generates induced current. The mechanical motion of the metal part acting like a solenoid generates counter induced voltage at the inductive load even when the metal part is only weakly charged. Such counter induced voltage, which is called “counter electromotive force” in electric motors, acts as energy that inhibits intended operation. Induced voltage, which is unavoidable during use of the inductive load, should preferably be removed immediately after its generation. 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    It is an object of the present invention to solve the above problems by providing an induced signal removing circuit that can remove induced voltage across a metal part insulated from an inductive load. 
       Solution to Problem 
       [0007]    The invention relates to an induced signal removing circuit for removing induced signals generated in a metal part in response to electrical signals input to an inductive load, including: an input terminal connected to the metal part insulated from the inductive load, the input terminal receiving the induced signals; two output terminals connected to an input side of the inductive load, the output terminal receiving the induced signals and outputting the induced signals, the input receiving electrical signals; and a signal flow controller between the input terminal and each output terminal, the controller causing the induced signals to flow in only one direction from the input terminal to each output terminal. 
       Advantageous Effects of Invention 
       [0008]    The present invention readily removes induced signals at a metal part insulated from an inductive load in an electrical circuit, leading to a smooth and efficient operation of the electrical circuit and preventing an electric shock caused by induced voltage. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a circuit diagram illustrating an example electrical circuit including an induced signal removing circuit of the invention. 
           [0010]      FIG. 2  is a schematic view of the induced signal removing circuit used as a speaker. 
           [0011]      FIGS. 3A and 3B  illustrate an advantage of the induced signal removing circuit. 
           [0012]      FIGS. 4A and 4B  illustrate an advantage of the induced signal removing circuit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0013]    Embodiments of an induced signal removing circuit of the invention will now be described with reference to the attached drawings.  FIG. 1  is a circuit diagram of an example induced signal removing circuit according to the invention. In  FIG. 1 , an induced signal removing circuit  1  of the invention is connected to an electrical circuit  2 . The induced signal removing circuit  1  includes one input terminal T 1  and two output terminals T 2  and T 3 . A signal flow controller  10  is provided between the input terminal T 1  and the output terminal T 2  and between the input terminal T 1  and the output terminal T 3 . Electrical signals (induced signals) input to the induced signal removing circuit  1  via the input terminal T 1  flow (are output) to the output terminal T 2  or T 3  in accordance with the signal flow controller  10 . 
         [0014]    The signal flow controller  10  includes a rectifier that forces induced signals from the input terminal T 1  to flow to the output terminal T 2  or T 3 . The signal flow controller  10  controls the flow direction of positive induced signals from the input terminal T 1  such that they are not output from the output terminal T 3  but from the output terminal T 2 . On the contrary, the signal flow controller  10  controls the flow direction of negative induced signals from the input terminal T 1  such that they are not output from the output terminal T 2  but from the output terminal T 3 . As shown in  FIG. 1 , the signal flow controller  10  consists of two diodes D 1  and D 2  serving as a rectifier. The signal flow controller  10  may consist of any element other than diodes that can control signal flow in the above manner. 
         [0015]    In the signal flow controller  10  in  FIG. 1 , the cathode of the diode D 1  corresponds to the output terminal T 1 , while the cathode of the diode D 2  corresponds to the output terminal T 3 . A protective resistor R 1  is provided between the anode of the diode D 1  and the input terminal T 1 . A protective resistor R 2  is provided between the anode of the diode D 2  and the input terminal T 1 . The input terminal T 1  is connected to the node of the resistors R 1  and R 2 . 
         [0016]    The induced signals, which are transient, may cause a sudden flow of high current. The protective resistors R 1  and R 2  are used to protect the diodes D 1  and D 2  from excessively high input signals, i.e., induced signals. The protective resistors R 1  and R 2  are not necessarily provided if damage to the diodes D 1  and D 2  is avoidable. The protective resistors R 1  and R 2  preferably have the same resistance. 
         [0017]    In  FIG. 1 , the reference numeral  2  represents an electrical circuit connected to the induced signal removing circuit  1 .  FIG. 1  only shows typical components: an input terminal  22  of the electrical circuit  2  to input signals to the inductive load  21 ; and a metal part  23  generating induced signals in response to the input signals. The input terminal  22  to input signals to the inductive load  21  consists of positive (+) and negative (−) terminals. 
         [0018]    The input terminal T 1  of the induced signal removing circuit  1  is connected to the metal part  23  generating induced signals caused by the inductive load  21  in the electrical circuit  2 . The output terminal T 2  is connected to a positive signal line while the output terminal T 3  is connected to a negative signal line for signals to the inductive load  21  (input signals actuating the inductive load). Positive (+) signals from the input terminal  22  of the electrical circuit  2  pass through the inductive load  21  from the positive electrode to the negative electrode. If signals from the input terminal  22  of the electrical circuit  2  are negative (−), current flows through the inductive load  21  from the negative electrode to the positive electrode. 
         [0019]    The direction of a signal input to the electrical circuit  2  determines the polarity of an induced signal generated in the metal part  23 . A negative induced signal input to the induced signal removing circuit  1  passes through the diode D 1  and then is output from the output terminal T 2 . The induced signal from the output terminal T 2  is fed to the positive signal line in the electrical circuit  2 . A positive induced signal generated in the metal part  23  is input to the induced signal removing circuit  1 , passes through the diode D 2 , and then is output from the output terminal T 3 . The induced signal from the output terminal T 3  is fed to the negative signal line in the electrical circuit  2 . 
         [0020]    As described above, the input terminal T 1  of the induced signal removing circuit  1  is connected to the metal part of the inductive load  21 , i.e., to a variable potential part due to electromagnetic induction caused by signals input to the inductive load  21 . The output terminals T 1  and T 2  of the induced signal removing circuit  1  are connected to the respective signal lines (or input terminals) that receive signals for actuating the inductive load  21 . Thus, induced signals based on variable potential due to electromagnetic induction can be fed to the input side receiving signals for actuating the inductive load  21 . This removes induced signals generated in the metal part  23 . 
         [0021]    The operation of the induced signal removing circuit  1  of this embodiment will now be described in detail in which the inductive load  21  is based on a solenoid mechanism, and the metal part  23  is a plunger in cooperation with the solenoid mechanism. Signals from the input terminal  22  cause the metal part  23  to operate in a predetermined manner. The metal part  23  linearly moves by means of a solenoid that converts electric energy into linear motion. The metal part  23  linearly moves in a magnetic field generated by current flowing through a coil in the inductive load  21 . Consequently, signals from the input terminal  22  generate induced voltage in the metal part  23 . Such linear motion of the metal part  23  with induced voltage in the coil generates counter electromotive force. 
         [0022]    The counter electromotive force causes current to flow in the direction opposite to that of kinetic energy generated by signals from the input terminal  22 . For this reason, the metal part  23  is connected to the input terminal T 1  of the induced signal removing circuit  1 , and the output terminals T 2  and T 3  of the induced signal removing circuit  1  are connected to the respective signal input lines of the solenoid, i.e., the inductive load  21 . This allows a variation in the voltage across the metal part  23  due to induction to be processed in the signal flow controller  10  and then appear at the output terminal T 2  or T 3  in the form of a signal. Thus, the induced signal removing circuit  1  superimposes induced signals generated in the inductive load  21  on signals to be input to the inductive load  21 . Such action allows the metal part  23  to have substantially zero potential. This prevents the generation of counter electromotive force and leads to efficient operation of the solenoid. Note that feeding induced signals to the inductive load  21  via the input terminal barely affects a unit (e.g., a power supply) that supplies signals actuating the inductive load  21 . 
         [0023]    An example operation of an induced signal removing circuit  1  with an inductive load being a speaker will now be described. In  FIG. 2 , a speaker  3  can emit sound by oscillating its cone in response to the vertical oscillation (in the drawing) of a coil cap to which the voice coil  32  is fixed. The vertical oscillation results from a magnetic field generated by a magnet around the voice coil  32  and current flowing through the voice coil  32  in response to signals from an input terminal  31 . 
         [0024]    The magnet  33  is in contact with a yoke  34  and a pole piece  35 . The yoke  34  and pole piece  35  are made of metals. The yoke  34  and the pole piece  35  are disposed such that the magnetic field generated by the magnet  33  works efficiently according to the voice coil  32 . As stated above, upon reception of an electrical signal from the input terminal  31 , the coil  32  vertically oscillates. The resulting current flows through the coil and generates a magnetic field that acts on metal parts, i.e., the yoke  34  and the pole piece  35 . This generates electromagnetically induced voltage in the metal parts. The induced voltage provides a force that moves the voice coil  32  in the direction opposite to the direction in which the voice coil  32  is moved by signals from the input terminal  31 . Thus, such induced voltage inhibits the motion of a diaphragm that emits sound based on signals from the input terminal  31 . 
         [0025]    To avoid such a phenomenon, the yoke  34  or pole piece  35 , or both is connected to the input terminal T 1  of the induced signal removing circuit  1 . The output terminal T 2  of the induced signal removing circuit  1  is connected to one end of the input terminal  31  of the speaker, whereas the output terminal T 3  is connected to the other end of the input terminal  31  of the speaker. 
         [0026]    A positive input signal fed to the speaker  3  generates induced voltage in the yoke  34  or pole piece  35 . The induced voltage signal (induced signal) input, for example, from the input terminal T 1  passes through the diode D 1 , is output from the output terminal T 2 , and then is input to the input terminal  31  of the speaker  3 . If the input signal is negative, an induced signal from the input terminal T 1  passes through the diode D 2 , is output from the output terminal T 3 , and then is input to the input terminal  31  of the speaker  3 . Induced signals are transient in response to variations in the input signals as described later, and thus do not greatly vary the input signals. Induced signals therefore do not cause noise mixed in the sound from the speaker  3 . 
         [0027]    Thus, the induced signal removing circuit  1  of the invention efficiently removes induced signals in an electrical circuit including an inductive load. The removal of the induced signals enables the inductive load to operate accurately in response to the input signals. 
         [0028]    How to remove induced signals with the induced signal removing circuit of the invention will now be described in detail with reference to drawings.  FIGS. 3A and 3B  schematically show how to measure the induced signals. In  FIG. 3A , the inductive load corresponds to the speaker  3 . The yoke  34 , which is a metal part of the speaker  3 , is grounded via a resistor  4 . This configuration causes induced signals in the metal part to pass to the ground via the resistor  4 . For this reason, a measuring device, e.g. an oscilloscope connected to the resistor  4  can measure the induced signals. 
         [0029]    If the speaker  3  receives an input signal (rectangular wave) as shown in  FIG. 3B , the voltage across the resistor  4  is observed as a differentiated signal of the input signal. Note that the resistor  4  has a resistance of approximately 1 MΩ. The signal shown in  FIG. 3B  that is observed at the resistor  4  corresponds to an induced signal. An induced signal is transient and decreases to zero in a certain period. Variations in the signal occur while the signal transiently decreases. During such a transient period, energy occurs that inhibits the above-described desired operation. 
         [0030]    To solve such a problem, as shown in  FIG. 4 , the induced signal removing circuit  1  is connected to the inductive load, i.e., the speaker. As shown in  FIG. 4A , the input terminal T 1  of the induced signal removing circuit  1  is connected to the yoke  34 . The output terminal T 2  is connected to one input terminal of the speaker  3 , whereas the output terminal T 3  is connected to the other input terminal of the speaker  3 . Consequently, as shown in  FIG. 4B , a rectangular wave does not substantially cause measurable voltage across the resistor  4 . This is because a transient induced signal exceeding a predetermined value passes through the diode D 1  or D 2  depending on its polarity, and then to the input terminal  31 . Since the minimum voltage applied to a diode is commonly 0.6 V, an induced signal of 0.6 V or higher generated from an input signal passes to the signal input terminal via the induced signal removing circuit  1 . Specifically, the induced signal removing circuit  1  feeds back induced signals, which inhibit the intended operation of the inductive load, into the input side of the inductive load, thus removing the induced signals. 
         [0031]    Thus, the induced signal removing circuit of the invention used in an electric device with a coil and a metal part can feed back induced signals generated in the metal part from signals input to the coil, into the input side of the inductive load, i.e., the source of induced signals, unlike a conventional measure which sends such induced signals to another metal part or grounding conductor. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  induced signal removing circuit 
           10  signal flow controller