Particle control method

1. 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.

2. The method according to claim 1 ,

comprising changing a distance separating away from the surface of the oscillation board by changing an output of the ultrasonic vibration of the oscillation board, and controlling the descent position of the chosen particle in an arbitrary direction.

3. The method according to claim 1 ,

wherein in the clean zone, the oscillation board is complemented by additional oscillation boards to form a plurality of pairs of oscillation boards such that two oscillation boards with their board surfaces facing each other substantially in parallel with the flow direction of the unidirectional air flow are disposed at an angle changed in a horizontal; and

by prompting ultrasonic vibration of said oscillation boards, forming a focal point of an ultrasonic wave in the direction perpendicular to each of the board surfaces and in the direction crossing the flow direction of the unidirectional air flow,

subjecting the particles made to flow by air in the unidirectional air flow and descending from the upper side toward the lower side, to the ultrasonic wave to guide the particles to the focal point of the ultrasonic wave so that the descent position is controlled to below a position of the focal point of the ultrasonic wave.

4. The method according to claim 1 ,

wherein in the clean zone, the oscillation board is complemented by a reflection board or another oscillation board to form a pair of boards having their board surfaces face each other substantially in parallel with the flow direction of the unidirectional air flow;

by prompting ultrasonic vibration of the pair of boards, generating a standing wave field by the ultrasonic wave in said direction that is perpendicular to each of the board surfaces and in said direction crossing the flow direction of the unidirectional air flow;

subjecting the particles, made to flow by air in the unidirectional air flow and descending from the upper side toward the lower side, to the ultrasonic wave to guide the particles to a node of the standing wave field so that the descent position is controlled to below a position of the node of the standing wave field.

5. The method according to claim 4 ,

wherein by relatively changing an output of the ultrasonic vibration of each of the oscillation boards, the position of the node of the standing wave field is changed so that the particle descent position is controlled to move in an arbitrary direction.

6. The method according to claim 4 ,

wherein the method is used for measuring an amount of particles descending through the clean zone or floating bacteria contained at said particles; and

opening a capturing port of the particle counter or a floating bacteria counter below the position of the node of the standing wave field and controlling a movement of said descending particles such that the descending particles or said floating bacteria contained in thcm are guided to the capturing port.