A screw capper 1 includes a capping head 6 which grips a cap 5, a servo motor 7 which rotates the capping head, a voltmeter 10 which measures the torque of the capping head, an encoder 11 which detects the rotational angle of the capping head, and a control device 8 which controls the servo motor. In the screw capper, whether rotational fastening is acceptable is to be determined during the rotational fastening, the measured value of the encoder is measured from a predetermined measurement starting point until a rotational fastening completion point, and if the measured rotational angle is in the range of an acceptable decision angle which is set in advance, it is determined that the rotational fastening has been acceptably performed, whereas if the measured rotational angle is not in the range of the acceptable decision angle, it is determined that the rotational fastening is unacceptable.In the screw capper, defective rotational fastening can be detected, and reductions in costs can be realized compared to a case where a device for detecting such defective rotational fastening is separately provided.
A metal cap 12 is fitted over a vessel (vial 2), into which a rubber plug 4 is driven, and using a pressure block 10, a load is applied to the cap 12 through the top surface 12b thereof to maintain the rubber plug 4 compressed. Under this condition, a tightening roller 14 folds a skirt (lower end 12c of a cylindrical portion 12a) of the cap 12 inwardly to perform a tightening operation. Subsequently, the load applied to the top surface 12b of the cap is once released, and then a load is applied again starting from a value FB which is less than the load FA applied during the tightening operation, gradually increasing to a higher value. In the course of increasing the load, a load FC at the instant when a displacement in the elevation of the top surface of the cap is detected, and this load FC is determined to be a seal load upon completion of the tightening operation. By detecting the load FC upon completion of the tightening operation, a seal capacity of the rubber plug 14 can be confirmed.
