A data storage system connectable to a host unit which issues data readwrite requests to the data storage system, and which includes a plurality of disc units, and a controller connected to the disc units. The data acquisition unit acquires echo signals by echo planar imaging which generates the echo signals by applying plural phase-encoding gradient magnetic field pulses and by repeatedly inverting a readout gradient magnetic field after one nuclear magnetic resonance excitation. The first clamping piece is configured with a spring that is capable of moving relatively to the fan so as to enable a first protrusion formed on the spring to inset into the hollow section when the spring is moved to a first position, and detach from the hollow section when the spring is move to a second position. Switched channels maintain status information about their current status, allowing switched data communication when the channel’s status is active, and permitting the unswitched data path to utilize the channel when the channel’s status is idle. Whether the human body or an obstacle enters the monitoring space, which is surrounded by a detection wave between the main body unit of the image projection apparatus and the screen, or not is detected.