| 摘要 |
A voltage value detected at the time of filling the liquid changes in accordance with viscosity. The voltage value is used as an indicator of the viscosity of the liquid at the time of a returning operation. Specifically, when the voltage value acquired at the filling time is low, the viscosity is determined as relatively high at the time of the returning operation, and a returning threshold value Th1 is set to a relatively high value. In concrete, the filling voltage is updated each time a filling operation is performed, and as the value of the filling voltage which is referred to at the time of the returning operation, the value which is acquired in the immediately preceding filling operation is used. Thereby, even when the liquid has relatively high viscosity, completion of the returning operation can be detected without increasing the time required before completion of the returning operation.
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