Capping method and apparatus

Abstract: A capping apparatus (1) includes torque measuring means (12) which detects an output torque when a chuck (7) is driven for rotation by a motor (9). Initially a cap (5) is held by the chuck (7), the cap (5) is fitted over a mouth of a vessel (2), and then the chuck (7) is rotated through one revolution in a clamping direction, a resulting output torque being detected by the torque measuring means (12), and the output torque rapidly increases at the position where the threads on the cap (5) and the vessel (2) abut against each other (an incipient position of meshing engagement (P). The cap (5) is rotated through a given angle of rotation as referenced to the incipient position of meshing engagement (P), thus threadably engaging the cap (5) with the vessel (2), the invention allowing a uniform clamping of cap (5) at the completion of the capping operation.

Description: The present invention relates to a capping method and apparatus, and more particularly, a capping method and apparatus in which an incipient position of a meshing engagement between threads on a vessel and threads on a cap is detected and then the cap is turned through a given angle of rotation as referenced to the detected position to clamp the cap onto the vessel. A capping method of the kind described is known in the art (see for example, Japanese Patent Publication No. 6115591A and Japanese Laid-Open Patent Application No. 11124196A ). In the disclosed method, the incipient position of a meshing engagement between the threads on the vessel and the threads on the cap is detected by initially fitting the cap over the threads on the vessel from above and turning the cap in a direction opposite from the direction in which it is clamped. The distal end of the threads on the cap which is located at the bottom thereof is disengaged from the top end of the threads on the vessel, whereby the cap falls down by a vertical distance corresponding to one pitch of the threads on the vessel vertically. In the conventional method, the point which the cap reaches upon descent through such a significant distance is detected as the incipient position of a meshing engagement between the threads on the vessel and the threads on the cap. According to the conventional method, the incipient position of meshing engagement between the both threads is determined on the basis of the magnitude of descent of the cap, and this requires the provision of means for detecting the descent disadvantageously. Such detecting means would include a vertically slidable component, which undergoes an abrasion, thus presenting a problem in respect of the durability. In addition, with the conventional method, in order to assure the descent of the cap, a turning of the cap in the opposite direction takes place under a clamping condition, i.e., while the threads on the cap are strongly urged against the threads on the vessel. A likelihood then arises that the threads on the cap and/or the vessel may be damaged. EP 0 618 168A discloses a capping apparatus according to the preamble of claim 4. In view of the foregoing, in accordance with one aspect of the present invention, there is provided a capping method as described in claim 1. According to another aspect of the invention, there is provided a capping apparatus including a capping head for holding a cap and a motor for rotating the capping head, the cap held by the capping head being turned in a clamping direction so that the cap can be clamped to a vessel with a predetermined winding angle, an elevating mechanism for elevating the capping head up and down; measuring means for measuring a change in a force acting on the cap which is held by the capping head; angle detecting means for detecting an angular position to which the capping head is rotated; and control means for controlling the rotation of the motor and receiving a result of measurement from the measuring means and an angle signal from the angle detecting means; characterised by the characterising portion of claim 4. With the described arrangement, the incipient position of a meshing engagement can be detected accurately, allowing the cap to be turned through a given angle of rotation as referenced to the incipient position, achieving a uniform clamping of caps to the vessels. Above and other features and advantages of the invention will become apparent from the following description of an embodiment thereof with reference to the attached drawings of which: Fig. 1 is a front view of essential parts of an embodiment of the invention; Fig. 2 is an illustration of a cap 5 before it is threadably engaged with a vessel 2 in the embodiment; Fig. 3 graphically shows a relationship between an elevational motion and a travel of a capping head in the embodiment; Fig. 4 is a diagram showing a relationship between a value of an output torque detected with a torque sensor and an angle of rotation of an encoder in the embodiment; and Fig. 5 is a similar view to Fig. 4. Referring to the drawings, an embodiment of the invention will now be described. A capping apparatus 1 includes a revolving body, not shown, which is rotatable in a horizontal plane. A plurality of receptacles 3 are disposed at an equal angular interval along the outer periphery of the revolving body, each receiving a vessel 2 thereon. A gripper 4 is associated with each receptacle 3 and is disposed on the revolving body to grip the barrel of the vessel 2. A capping head 6 is located above each receptacle 3 for holding a cap 5 for threadable engagement with the mouth of the vessel 2. As shown in Fig. 2, on its outer peripheral surface, the mouth of the vessel 2 is formed with male threads 2a while the inner peripheral surface of the cap 5 is formed with female threads 5a. The capping head 6 includes a chuck 7, which is known in itself, for detachably holding the cap 5 under pneumatic pressure, and a pair of upper and lower splined shafts 8a, 8b which are coupled to the chuck 7. The splined shafts 8a, 8b are mechanically coupled to a motor 9, the operation of which is in turn controlled by a controller 11. Thus, when the motor 9 is set in motion to rotate the splined shafts 8a, 8b and the chuck 7 in a direction to clamp the cap, the cap 5 which is held by the chuck 7 is threadably engaged around the mouth of the vessel 2. Torque measuring means 12 which measures a force acting upon the cap 5 held by the capping head 6 as a rotational load, and an encoder 13 acting as angle detecting means are connected to the motor 9. In this manner, when the motor 9 is set in motion, an output torque from the motor 9 is detected by the torque measuring means 12, with a result of measurement being fed to the controller 11. At the same time, an angular position of rotation of the motor 9 is detected by the encoder 13, which feeds an angle signal to the controller 11. The splined shafts 8a, 8b are constructed to be slidable through a given stroke relative to each other in the axial or vertical direction, and buffer spring 14 is disposed between the chuck 7 and the upper splined shaft 8a. As a consequence, before the cap 5 is mounted on the vessel 2, the chuck 7 is urged to its lowermost position with respect to the upper splined shaft 8a. Each capping head 6 and its associated motor 9 are arranged to be elevatable up and down by an elevating mechanism which comprises an annular elevating cam, not shown, which is disposed along the outer circumference of the revolving body. To achieve a threadable engagement of the cap 5 around the mouth of the vessel 2, the elevating cam causes the capping head 6 and the motor 9 to move from their raised end positions to their descended end positions, whereby the cap 5 held by the chuck 7 is fitted over the upper end of the vessel 2 and is urged downward. This causes the spring 14 to be compressed, whereby the chuck 7 and its connected lower splined shaft 8b are raised upward relative to the upper splined shaft 8a while urging the cap 5 held by the chuck 7 against the vessel 2. When the controller 11 sets the motor 9 in motion to rotate the chuck 7 in the clamping direction while the cap 5 is urged in this manner, the female threads 5a on the cap 5 are ready for threadable engagement with the male threads 2a on the vessel 2. Subsequently as the cap 5 is released from the holding action of the chuck 7, the capping head 6 is raised to its original raised position under the influence of the elevating cam. In this embodiment, on the basis of a change in the value of output torque detected by the torque measuring means 12 as the motor 9 is set in motion, a position P where the upper end 2a' of the male threads 2a on the vessel 2 (upper distal end of the male threads) is contacted by the lower end 5a' of the female threads on the cap 5 (lower distal end of the female threads) is detected which is defined as the incipient position of a meshing engagement therebetween. The cap 5 is then turned through a given angle of rotation as referenced to the incipient position in the clamping direction by means of the motor 9 for achieving a capping operation. Specifically, referring to Fig. 3, the cam surface of the elevating cam is formed with a descent stop zone A toward the left end, as viewed in Fig. 3, where the capping head 6 ceases to descend and maintains a same elevation while its travel. The descent stop interval A is provided in the course of a descent of the capping head 6 to the elevation of the clamping zone B at a location where the cap 5 is fitted over the vessel 2, but before the female threads 5a on the cap 5 are urged against the male threads 2a on the vessel 2 by the spring 14. The action of the capping head 6 to urge the cap 5 begins before the elevating cam reaches its lowermost point, and accordingly, the beginning point of a clamping zone B is located short of the lowermost point in Fig. 3. When the capping head 6 is positioned in the descent stop zone A, the cap 5 held by the capping head 6 has an elevation which is chosen to be such that the lowest extremity of the lower end 5a' of the female threads 5a on the cap 5 can abut vertically against the top extremity of the upper end 2a' of the male threads 2a on the vessel 2, as shown in Fig. 2. If the cap 5 is turned at this elevation, it is assured that the lower end 5a' of the female threads 5a abuts against the upper end 2a' of the male threads 2a on the vessel 2 during such rotation, producing a rotational load which is applied to the cap 5. In the present embodiment, while the capping head 6 ceases its descent in the descent stop zone A, the torque measuring means 12 detects an output torque from the motor 9 while the controller 11 causes the motor 9 to rotate through one revolution in either forward or reverse direction, thus causing the cap 5 held by the chuck 7 on the capping head 6 to rotate through one revolution either forwardly or reversely. When the cap 5 is rotated through one revolution, it follows that the lower end 5a- of the female threads 5a on the cap 5 once abuts against the upper end 2a' of the male threads 2a on the vessel 2 during such rotation, and at the instant of abutment, an output torque or a rotational load which has a maximum magnitude during the one revolution rotation of the cap 5 is measured. When a result of this measurement is input to the controller 11, the latter recognizes a prevailing angular position by means of the encoder 13. Fig. 4 shows a relationship between the output torque detected by the torque measuring means 12 with respect to the angular position of rotation of the motor 9 or the angular position of rotation of the cap 5 and the capping head 6 detected by the encoder 13 during the time the motor 5 causes the cap 5 to rotate through one revolution in the clamping direction. When the lower end 5a- of the female threads 5a on the cap 5 abuts against the upper end 2a' of the female threads 2a on the vessel 2, there occurs a rapid increase in the output torque as indicated by a peak in Fig. 4. This position represents the incipient position P of meshing engagement. It is to be noted that the torque measuring means 12 is designed to measure the magnitude of the current which is supplied to the motor 9. Thus, the magnitude of the current supplied to the motor 9 increases when there is a rotational load. This is indirectly determined as a change in the output torque, and the incipient position of meshing engagement P is detected as an angular position of rotation where the magnitude is equal to or greater than a given value. Where the cap 5 is rotated through one revolution in the reverse direction or in a direction opposite from the clamping direction by means of the motor 9, the current supplied will be represented as a negative value, and a resulting change in the output torque will be indicated by a negative peak as shown in Fig. 5. While the magnitude of the current supplied to the motor 9 is detected as an indication of the output torque by the torque measuring means in the above description, it should be understood that the magnitude of the voltage across the motor 9 may be used instead, or alternatively, an actual output torque may be directly detected. Although the incipient position of meshing engagement P can be detected in the manner mentioned above, it is to be noted that in the present embodiment, because the cap 5 is rotated through one revolution, the cap 5 comes to a stop beyond the incipient position of meshing engagement P. In addition, the position where it comes to a stop varies from time to time. Accordingly, the controller 11 calculates, as an offset  1, an angle of rotation from the start position where the motor 9 or the chuck 7 begins to rotate or the position where the chuck 7 or the cap 5 which remains stationary presently assumes to the incipient position of meshing engagement P as viewed in the clamping direction (Fig. 4) when the cap 5 is rotated in the forward direction. When the cap 5 is rotated in the reverse direction, the offset  1 is calculated as an angle of rotation from the incipient position of meshing engagement P to the stop position, as viewed in the direction opposite from the clamping direction. In the present embodiment, the controller 11 is preset to cause the cap 5 to rotate through a given angle  2 from the incipient position of meshing engagement P, and accordingly, the controller 11 adds the offset  1 to the given angle of rotation  2 to determine the angle of rotation  3 through which the motor 9 is to be rotated in the clamping direction. When the capping head 6 has moved past the descent stop zone A and again descended to cause the female threads 5 on the cap 5 to be urged against the male threads 2a on the vessel 2, and the capping head 6 is thus positioned in the clamping zone B, the controller 11 causes the motor 9 to rotate again through the angle of rotation  3 in the clamping direction, thus rotating the chuck 7 through the angle of rotation  3 in the clamping direction. Thereupon, the cap 5 which is held by the chuck 7 is rotated through the angle of rotation  3 from the stop condition which it presumed previously, whereby the cap 5 is rotated through the given angle of rotation  2 from the incipient position of meshing engagement P in the clamping direction, thus allowing the female threads 5a on the cap 5 to be clamped around the male threads 2a on the vessel 2 with a predetermined winding angle. The capping apparatus 1 of the present embodiment is constructed to allow the cap 5 to be threadably engaged around the mouth of the vessel 2 in this manner. It is to be understood that the incipient position of meshing engagement P merely represents a reference position, and if the configuration of the threads on the vessel and/or cap is modified, such position moves back and forth. To achieve a required winding angle, an optimum winding angle which is referenced to the incipient position of meshing engagement which is determined for a particular combination of a vessel and a cap which are to be capped together is previously determined, and is chosen as a given angle  2. Thus it will be seen that in the present embodiment, the incipient position of meshing engagement P is detected in terms of a change in an output torque from the torque measuring means 12, and the cap 5 is rotated through the given angel of rotation  2 as referenced to the incipient position of meshing engagement P thus determined, thus causing it to be threadably engaged with the vessel 2. This allows the incipient position of meshing engagement P to be detected accurately, and a subsequent clamping operation takes place always uniformly as the cap 5 is capped to assure a capping operation of a high precision. As an alternative to the described technique, the detection of the incipient position of meshing engagement P may comprise a sampling of an output torque by means of the controller 11 each time the motor 9 rotates through one revolution, and comparing a current sample against a previous sample. If there is a rapid increase in the output torque, this may be used as an indication of the incipient position of meshing engagement P. In the embodiment mentioned above, the motor 9 is caused to rotate through one revolution and to stop then in the descent stop zone A. However, the rotation of the motor 9 may be stopped upon detection of the incipient position of meshing engagement P where there occurs a rapid increase in the output torque. It should be understood that the addition of the offset  1 is omitted in this instance.

Claims: A method of detecting an incipient position of meshing engagement (P) between a thread (2a) of a vessel (2) and a thread (5a) of a cap (5) and of clamping the cap (5) to the vessel (2) with a predetermined winding angle, which uses a capping head (6) for holding the cap (5) and a motor (9) for rotating the capping head (6) to turn the cap (5) held by the capping head (6) in a clamping direction so that the cap (5) can be clamped to a vessel (2), the method including the step of: causing the cap (5) held by the capping head (6) to descend so as to be fitted around a mouth of the vessel (2); stopping the descent at an elevation where a distal end that is a lower end of the thread (5a) of the cap (5) can abut against a distal end that is an upper end of the thread (2a) of the vessel (2) but where the threads (2a, 5a) do not make threaded engagement with each other; relatively rotating the thread (5a) of the cap (5) and the thread (2a) of the vessel (2) at the elevation where the descent is stopped; measuring a change of force acting on the cap (5), thereby to detect an incipient position of meshing engagement (P) on the basis of the change of force; resuming the descent of the cap (5); and rotating the cap (5) by a predetermined rotational angle with the incipient position of meshing engagement (P) as a reference. A method according to claim 1, wherein a change of torque acting on the cap (5) is measured to detect the incipient position of meshing engagement (P). A method according to claim 2, wherein the relative rotation of the thread (5a) of the cap (5) and the thread (2a) of the vessel (2) is in a direction opposite from the clamping direction such that the incipient position of meshing engagement (P) is detected when the torque changes from an increasing state to a decreasing state. A capping apparatus having: a capping head (6) for holding a cap (5); a motor (9) for rotating the capping head (6) to turn a cap (5) held by the capping head (6) in a clamping direction so that the cap (5) can be clamped to a vessel (2) with a predetermined winding angle; an elevating mechanism for elevating the capping head (6) up and down; measuring means for measuring a change in a force acting on the cap (5) held by the capping head (6); angle detecting means for detecting an angular position to which the capping head (6) is rotated; and control means (11) for controlling the rotation of the motor and receiving a result of a measurement from the measuring means and an angle signal from the angle detecting means; characterised in that : the elevating mechanism is adapted to stop temporarily during a descent of the capping head (6) at an elevation where a distal end that is a lower end of the thread (5a) of the cap (5) can abut against a distal end that is an upper end of the thread (2a) of the vessel (2) but where the threads (2a, 5a) do not make threaded engagement with each other; the control means is arranged such that the thread (5a) of the cap (5) and the thread (2a) of the vessel (2) are rotated relative to each other at the elevation where the descent is stopped so that, when a change of force acting on the cap (5) is measured: an incipient position of meshing engagement (P) is detected on the basis of the result of the measurement, descent of the cap (5) resumes, and the cap (5) is rotated by a predetermined rotational angle with the incipient position of meshing engagement (P) as a reference. A capping apparatus according to claim 4, wherein the measuring means measures a change of torque acting on the cap (5).

Inventors: KITAMOTO HIROAKI, KITAMOTO, HIROAKI, Kitamoto, Hiroaki, Shibuya Kogyo Co., Ltd.
Applicants: SHIBUYA KOGYO CO LTD, SHIBUYA KOGYO CO., LTD
Application year: 2001
Main classification: B67B3
IPC codes: G01L5, B67B3