Rotation detector including a controller to obtain states of detection coils

A rotation detector to detect a rotation direction and a number of rotations of a rotation shaft, the rotation detector comprising:

• a rotation detection mechanism attached to the rotation shaft to detect rotations of the rotation shaft;
• and
• a signal processing circuit electrically connected to the rotation detection mechanism, wherein
• the rotation detection mechanism includes
• a magnet configured to rotate in synchronization with the rotation shaft and having an N number of magnetic poles arranged in a rotation direction, and
• an L number of detection coils arranged at positions displaced from each other by a predetermined phase in the rotation direction of the magnet, N being a natural number of two or more, L being a natural number of three or more,
• each of the L number of detection coils is configured to receive a magnetic field applied from the magnet and generate a voltage pulse of a positive or negative polarity,
• the signal processing circuit includes
• a constant voltage circuit to generate, every time a voltage pulse is generated, a source voltage from electric power of the voltage pulse, and
• a controller and a non-volatile memory to operate upon receipt of the source voltage,
• the non-volatile memory is configured to store states of the L number of detection coils and the number of rotations of the rotation shaft in generation of a voltage pulse, and a history of information on a detection coil that has generated the voltage pulse,
• the controller is configured to, every time a voltage pulse is generated, obtain the states of the L number of detection coils, the number of rotations of the rotation shaft, and the information on a detection coil that has generated the voltage pulse, and perform a process of updating the non-volatile memory,
• in the process of updating, by referring to information on a current voltage pulse, and states of the L number of detection coils in generation of the last voltage pulse, states of the L number of detection coils in generation of the last but one voltage pulse, and a history of information on a detection coil that has generated the last but one voltage pulse, which are held in the non-volatile memory, the controller detects a pulse dropout in which a voltage pulse drops out, and corrects the states of the L number of detection coils and the number of rotations of the rotation shaft that are to be held in the non-volatile memory,
• the controller is configured to change a state of each of the L number of detection coils to a first logic level upon generation of the voltage pulse of the positive polarity and to a second logic level upon generation of the voltage pulse of the negative polarity and estimate a rotational position of the magnet from the states of the L number of detection coils, and
• in the process of updating, the controller
• detects the pulse dropout and estimates a transition of the rotational position of the magnet by referring to the rotational position of the magnet estimated from each of the states of the L number of detection coils in generation of the last voltage pulse and the states of the L number of detection coils in generation of the last but one voltage pulse, and the history of the information on the detection coil that has generated the last but one voltage pulse, which are held in the non-volatile memory, and
• based on the estimated transition of the rotational position of the magnet, corrects the states of the L number of detection coils and the number of rotations of the rotation shaft that are to be held in the non-volatile memory.