Displacement measuring apparatus

A control apparatus of a displacement measuring apparatus, the control apparatus comprising:

• a signal processing unit configured to receive at least two sensor signal sets from a displacement sensor and to process the at least two sensor signal sets, each set comprising at least one sensor signal, each sensor signal of the at least two sensor signal sets having a value dependent on a sensed displacement or position, and sensor signals in each sensor signal set having a period different from sensor signals in each other sensor signal set;
• and
• an operation-mode control unit configured to switch an operation mode of the signal processing unit, wherein
• the operation mode of the signal processing unit includes:
• a measurement operation execution mode to calculate the displacement or position as a measurement value using the at least two sensor signal sets obtained from the displacement sensor;
• and
• a sleep mode to reduce power consumption compared to the measurement operation execution mode,
• the signal processing unit performs, in the sleep mode, a substitute calculation process at a predetermined sampling frequency to sequentially calculate substitute values related to the displacement or position, each substitute value being calculated using a corresponding part of the sensor signals obtained from less than all of the at least two sensor signal sets to be used in the measurement operation execution mode, and
• the operation-mode control unit detects a variation of the displacement sensor when there is a variation in the substitute values, and in response to the detection, cancels the sleep mode and switches the signal processing unit to the measurement operation execution mode.

A control method of a displacement measuring apparatus, the displacement measuring apparatus comprising:

• a signal processing unit configured to receive at least two sensor signal sets from a displacement sensor and to process the at least two sensor signal sets, each set comprising at least one signal phase, each sensor signal of the at least two sensor signal sets having a value dependent on a sensed displacement or position, and sensor signals in each sensor signal set having a period different from sensor signals in each other sensor signal set;
• and
• an operation-mode control unit configured to switch an operation mode of the signal processing unit, the operation mode of the signal processing unit including:
• a measurement operation execution mode to calculate the displacement or position as a measurement value using the at least two sensor signal sets obtained from the displacement sensor;
• and
• a sleep mode to reduce power consumption compared to the measurement operation execution mode, the control method comprising:
• performing, by the signal processing unit a substitute calculation process at a predetermined sampling frequency in the sleep mode to sequentially calculate substitute values related to the displacement or position, each substitute value being calculated using a corresponding part of the sensor signals obtained from less than all of the at least two sensor signal sets to be used in the measurement operation execution mode;
• and
• detecting, by the operation-mode control unit, a variation of the displacement sensor when there is a variation in the substitute values, and in response to the detection, cancelling the sleep mode and switching the signal processing unit to the measurement operation execution mode.

A non-transitory recording medium storing a control program for a displacement measuring apparatus causing, by incorporating a computer in a control unit of the displacement measuring apparatus, the computer to perform functions of:

• a signal processing unit configured to receive at least two sensor signal sets from a displacement sensor and to process the at least two sensor signal sets, each set comprising at least one signal phase, each sensor signal of the at least two sensor signal sets having a value dependent on a sensed displacement or position, and sensor signals in each sensor signal set having a period different from sensor signals in each other sensor signal set;
• and
• an operation-mode control unit configured to switch an operation mode of the signal processing unit, wherein
• the operation mode of the signal processing unit includes:
• a measurement operation execution mode to calculate the displacement or position as a measurement value using the at least two sensor signal sets obtained from the displacement sensor;
• and
• a sleep mode to reduce power consumption compared to the measurement operation execution mode,
• the signal processing unit performs, in the sleep mode, a substitute calculation process at a predetermined sampling frequency to sequentially calculate substitute values related to the displacement or position, each substitute value being calculated using a corresponding part of the sensor signals obtained from less than all of the at least two sensor signal sets to be used in the measurement operation execution mode, and
• the operation-mode control unit detects a variation of the displacement sensor when there is a variation in the substitute values, and in response to the detection, cancels the sleep mode and switches the signal processing unit to the measurement operation execution mode.