Method for controlling gas-pressure-driven apparatus and gas-pressure-driven apparatus

A gas-pressure-driven apparatus comprising:

• a main body having a working chamber to which a working gas is supplied and from which the working gas is discharged;
• a supply and discharge section configured to supply the working gas to the working chamber and to discharge the working gas from the working chamber;
• a movable member configured to move relative to the main body in accordance with a pressure of the working chamber;
• a pressure sensor configured to detect a pressure of a space including the working chamber;
• a flow rate sensor configured to detect a flow rate of the working gas flowing into and flowing out of the working chamber;
• and
• a control section which is configured to create a state in which a volume of the working chamber cannot be changed, to change the pressure of the working chamber in this state by controlling the supply and discharge section, and to calculate a pressure change amount on the basis of the pressure detected by the pressure sensor and to calculate an integrated flow rate on the basis of the flow rate detected by the flow rate sensor when the pressure of the working chamber is changed, the control section being configured to calculate an initial volume of the working chamber on the basis of the pressure change amount and the integrated flow rate, and to calculate a post-change volume of the working chamber after its volume has changed on the basis of the initial volume and the integrated flow rate calculated from the flow rate detected by the flow rate sensor after creation of a state in which the volume of the working chamber can be changed from the initial volume,
• wherein the control section is further configured to calculate a pressure change corresponding to a flow rate of the working gas which contributes to a change in the pressure of the working chamber on the basis of the post-change volume and the pressure detected by the pressure sensor, and to calculate the integrated flow rate on the basis of a change in the volume of the working chamber which is calculated by subtracting the pressure change corresponding flow rate from the flow rate detected by the flow rate sensor.