Particle control method

A method for controlling movement of particles in a clean zone through which a unidirectional air flow flows from an upper side toward a lower side in a work chamber,

• wherein the work chamber comprises an oscillation board having a surface thereof disposed substantially in parallel with a flow direction of the unidirectional air flow, the method comprising the steps of:
• subjecting the oscillation board to an ultrasonic vibration so as to generate an acoustic flow by the ultrasonic wave in a direction perpendicular to the surface of oscillation board and in a direction crossing the flow direction of the unidirectional air flow;
• operating the oscillation board such that the ultrasonic wave is made to act on particles in the unidirectional air flow and descending from the upper side toward the lower side so that the descent position of the particles is controlled, and
• subjecting the particles, made to flow by air in the unidirectional air flow and descending from the upper side toward the lower side, to a pressing force by an acoustic radiation pressure so that a descent position of a chosen particle from said descending particles is controlled in a direction away from the surface of the oscillation board,
• wherein said surface of the oscillation board is disposed in one plane only, which one plane is substantially parallel to said flow direction of the unidirectional air flow;
• wherein the method is configured to prevent the descending particles from being mixed in opening portions of a plurality of containers continuously traveling in the clean zone and having upper sides open,
• wherein the surface of the oscillation board is disposed substantially in parallel with a traveling direction of the plurality of containers so that the descent position of a chosen particle is controlled so as to be at a location beyond an opening portion, of a container from said plurality, from the surface.