Apparatus for controlling a star wheel for positioning specimen

Abstract

An apparatus for controlling a star wheel for precise positioning of specimen containers in circumferentially successive segments of the star wheel. The apparatus includes at least two sensor arrays, each including a transmitter and receiver, which are angularly offset from one another in the plane of rotation of the star wheel and face end surfaces of segmental vanes of the star wheel. Each time the star wheel reaches a defined angular position, one of the sensor arrays responds, and the output signal of this sensor array, via a control circuit, triggers a drive motor for the star wheel such that its rotational speed is reduced, and the output signal of the other sensor array, when the same segment moves past it, stops the motor. With this kind of two-stage triggering of the motor, the inertia of such a star wheel in its rotation is taken into account, so that the star wheel is controllable exactly in such a way that the specimen containers come to a stop successively and with high precision at the desired stopping position, where one or more processing steps, such as a measurement of luminescence, can be performed. By scanning the star wheel with the two sensor arrays directly at its circumference, additional components such as control disks, which are an additional source of error and reduce the precision, can be dispensed with.