Capping machine

A capping machine for capping a container having a screw-threaded neck portion with a correspondingly screw-threaded cap. The machine comprises retaining means for retaining such a container in a retaining position and a rotary chuck for holding such a cap above the capping position, forward and reverse rotary drive means coupled to the chuck for rotating such a cap in both a clockwise sense and an anticlockwise sense, rotary movement monitoring means constructed and positioned to monitor rotation of the chuck, linear motion means coupled to the chuck to move the chuck both downwardly and upwardly, screwthread-disengagement monitoring means arranged to monitor when the screwthreads of such a cap and neck disengage momentarily as the cap is rotated in the unscrewing sense on the neck and the linear motion means urge the chuck downwardly, and control means connected to the rotary drive means, the rotary movement monitoring means, and the screwthread-disengagement monitoring means. The control means are such as to rotate the cap in the unscrewing sense, monitor the relative angular position of the cap when the screwthreads of the cap and the neck momentarily disengage, by means of the screwthread-disengagement means, and then to rotate the cap in the screwing sense by a predetermined amount dependent upon the length of the screwthreads.

The present invention relates to a capping machine for screwing 
screw-threaded caps on containers. 
In previously proposed capping machines, screwthreaded caps are screwed 
onto bottles or other containers by such capping machines using indirectly 
powered vertical shafts with cap holding chucks mounted at the lower ends 
of these shafts. In each case the shaft is rotated in the cap-tightening 
sense, and the shaft is lowered onto the container to be capped whereupon 
the cap engages the container thread and is tightened. In an endeavour to 
obviate over-tightening of the screw-threaded caps a slipping clutch 
arrangement is normally provided in the chuck, or by stalling of the motor 
when the cap is tight. 
Such machines have the following disadvantages: 
1) high chuck angular velocities are required to allow a high throughput of 
capped containers by the machine, but high chuck angular velocities cause 
the stored energy of the rotating mass to produce over-tightened caps in 
spite of the slipping clutch arrangement or motor stalling 
characteristics; 
2) low chuck angular velocities are required to prevent the inertial 
effects producing overtorque in the capping operation, but such low 
angular velocities prevent a high machine throughput; 
3) there is no provision for checking that the cap is engaged and properly 
tightened; 
4) such tightening control means, whether they be simple friction or 
magnetic devices, or the construction of motor that gives rise to desired 
stall characteristics, results in arbitrary calibration. Furthermore, in 
the case of slipping clutches, there tends to be a calibration drift owing 
to the lack of real time calibration; 
5) there is no method of measuring actual torque, directly from the torque 
applying parts of the machine, that takes account of inertial forces 
applied to the cap during the capping operation; 
6) there is no method of monitoring the quality achieved in capping 
operations, such as checking for damaged or crossed threads, broken caps, 
or presence of foreign material in the thread region; and 
7) changing the capping head to take different cap sizes involves 
mechanical adjustments with the attendant problems of inaccuracy, and it 
is not normally practical to change the machine speed to allow for 
different cap characteristics. 
It is an aim of the present invention to provide a capping machine which 
obviates one or more of these problems. 
Accordingly the present invention is directed to a capping machine for 
capping a container having a screwthreaded neck portion with a 
correspondingly screw-threaded cap, the machine comprising retaining means 
for retaining such a container in a retaining position and a rotary chuck 
for holding such a cap above the capping position, forward and reverse 
rotary drive means coupled to the chuck for rotating such a cap in both a 
clockwise sense and an anticlockwise sense, rotary movement monitoring 
means constructed and positioned to monitor rotation of the chuck, linear 
motion means coupled to the chuck to move the chuck both downwardly and 
upwardly, screwthread-disengagement monitoring means arranged to monitor 
when the screwthreads of such a cap and neck disengage momentarily as the 
cap is rotated in the unscrewing sense on the neck and the linear motion 
means urge the chuck downwardly, and control means connected to the rotary 
drive means, the rotary movement monitoring means, and the 
screwthread-disengagement monitoring means, the control means being such 
as to rotate the cap in the unscrewing sense, monitor the relative angular 
position of the cap when the screwthreads of the cap and the neck 
momentarily disengage, by means of the screwthread-disengagement means, 
and then to rotate the cap in the screwing sense by a predetermined amount 
dependent upon the length of the screwthreads. 
Preferably, the control means are such as to rotate the cap in the screwing 
sense by the said predetermined amount at a relatively high angular 
velocity and/or rate of change of angular velocity, and then to rotate the 
cap in that sense by a further amount, which is small relative to the said 
predetermined amount, at a relatively low angular velocity and/or rate of 
change of angular velocity, to tighten the cap on the neck. 
Store means may be provided in the control means to store the values of the 
said predetermined amount and/or the said further amount. 
The control means may be such as to run an initialising procedure at the 
start of a capping run, in which such a cap is screwed onto such a neck at 
a slow angular velocity, a measure of the screwthread length is made, and 
the said predetermined amount and the said further amount are determined 
and stored in the store means. 
Preferably the rotation of the cap by the said predetermined amount is 
effected by both an angular acceleration and also by a subsequent angular 
deceleration. 
The screwthread-disengagement means may comprise torque monitoring means 
coupled to the rotary drive means to monitor the torque applied by the 
latter, the torque monitoring means also being connected to the control 
means, the latter monitoring the relative angular position of the cap on 
the neck when such torque changes as the screwthreads momentarily 
disengage. 
Preferably, however, the screwthread-disengagement means comprise linear 
motion monitoring means constructed and positioned to monitor downward and 
upward movement of the chuck, the linear motion monitoring means also 
being connected to the control means, the latter monitoring the relative 
angular position of the cap on the neck when the chuck moves downwardly as 
the screwthreads of the cap and neck momentarily disengage. 
Preferably when the container has been capped the chuck applies a torque in 
the unscrewing sense which is a predetermined fraction of the desired 
tightening torque, to test the capping. This has the advantage that the 
tightness of the capping can be checked. 
The rotary drive means used, may be speed controlled, or torque controlled, 
or speed and torque controlled in accordance with the desired container to 
be capped.

In FIGS. 1 and 2, containers 10, which are to be capped, are fed by a 
conveyor system (not shown) to the capping machine. Once the containers 10 
reach the capping machine, they are held by a capping turret or retaining 
means 12. The capping turret 12 is rotatable around a central axis 14. The 
capping turret 12 is equipped with a hollow chuck shaft 16, which is 
disposed above the container feed path. The chuck shaft 16 is equipped 
with a chuck 18 at its lower end. The chuck shaft 16 is rotatable by a 
motor or rotary drive means 20 through a gear drive 22. The motor 20 and 
gear drive 22 are connected by a drive shaft 24. The drive shaft 24 also 
has fixed on it rotary movement monitoring means in the form of a shaft 
encoder 26 which monitors the rotation of the drive shaft 24, the rotation 
of the drive shaft 24 being proportional to the rotation of the chuck 
shaft 16. The output of the shaft encoder 26, which provides a pulse train 
absolutely related to the angular position of the motor shaft, is 
connected to a computer controller or control means 28. The motor 20 is 
controlled by a motor driver 30. The computer controller 28 is connected 
to the motor driver 30 to send signals thereto for controlling the angular 
velocity and torque applied by the chuck 18. An output from the motor 
driver 30 is also connected to the computer controller 28 to send signals 
back thereto and thus indicate the torque applied by the chuck 18. The 
chuck shaft 16 has a bracket 32 mounted on it (via a housing not shown in 
FIG. 1). The bracket 32 is connected to a cam follower 34 which, by 
following a cam 35, lowers the chuck shaft 16 in order to cap a container 
10 and then raises it once this operation is complete. The level of the 
chuck shaft 16 is monitored via a vertical movement sensor 36, which is 
positioned adjacent to the chuck shaft 16. The output of the vertical 
movement sensor 36 is connected to the computer controller 28. The capping 
machine is further equipped with a cap transfer arm 38. The arm 38 
transfers caps 40 from a cap feed chute (not shown) to a position above 
the container 10 to be capped, where it is picked up by the chuck 18. The 
items contained within the dotted line box in FIG. 1 are normally housed 
in a capping module 44. 
FIG. 2 shows schematically the path of the container 10 through the capping 
machine. The container 10 is fed onto the capping turret 12. The turret 12 
has four capping positions, which are angularly spaced apart from one 
another by 90.degree.. The turret 12 rotates in a clockwise sense when 
viewed from above, and moves in 90.degree. increments. When the container 
10 has been moved through 90.degree., it is under the position where the 
chuck 18 picks up the cap 40 and starts to apply it to the container 10. 
The capping operation is completed by the time the turret 12 beings to be 
rotated a further 90.degree. and the container 10 is set on to another 
conveyor belt to take it away for labelling and packing. To the side of 
the capping turret 12 there is the cap transfer arm 38 which pivots about 
one of its ends. The other end picks up caps 40 from the cap feed chute, 
and it is this end of the arm which, when swung, moves under the chuck 18. 
The feeding of the caps from the cap feed chute is controlled by a cap 
gate 42 which is activated (by means not shown) to feed another cap by the 
return of the empty arm 38. 
FIG. 3 shows the control connections of the capping machine as described 
above. The signals exchanged between the shaft encoder 26 and the vertical 
movement sensor 36 are digital and those between the motor driver 30 and 
the computer controller 28 are analogue. The motor driver 30 is an 
amplifier which amplifies the signals provided by the computer controller 
28. The computer controller 28 is in the form of a single board and 
provides capping data for retrieval and accepts downloadable parameters 
from the input control (not shown) programmed by the operator. 
FIG. 4 shows the capping module 44 in axial-section. The elements of the 
capping module are contained within a housing 46. The capping module 44 is 
mounted on the capping machine via a sliding bearing 48. A line 50 
providing the chuck air supply is connected to an upper end of the hollow 
chuck shaft 16. The centre of the chuck shaft 16 is in airtight 
communication with the line 50, there being a rotary seal 54 between the 
line 50 and the chuck shaft 16. The hollow central section of the chuck 
shaft 16 extends down to a pneumatic chuck head adaptor 56. The chuck head 
adaptor 56 has an inverted U-shape in section. 
The chuck head 57 contains a piston 59. The piston 59 has a gas-tight seal 
with the edges of the inside of U-shaped head adaptor 56. The piston 59 
seals a space 60 which is in gas communication with the chuck air supply 
via the shaft 16 and the line 50. The piston 59 has pivotally attached 
round its circumference a number of jaws 62. The jaws 62 have a sloping 
outside surface such that when the piston 59 is pushed downwards by air 
pressure they are pivoted inwards towards the central axis of the module 
44 by contact with a lip 63 on the lower end of the head 57. As a result 
of this action the jaws 62 grip the cap 40 to enable the container 10 to 
be capped. 
The shaft 16 is rotated by the motor 20. The motor 20 rotates the shaft 16 
via the gear drive 22. The shaft encoder 26 is mounted in the motor 
housing 20. The shaft encoder 26 monitors the rotation of the shaft 16 via 
the gear shaft 24 and the gear drive 22. The head adaptor 56 is supported 
for rotation, via the shaft 16, by the main bearings 72 which are mounted 
between the shaft 16 and the housing 46. 
The shaft 16 is provided with axially extending splines 64 which slidingly 
interengage axially extending splines 65 of the shaft gear 66 of the gear 
drive 22. Downward movement of the shaft 16 relative to the housing 46 is 
limited by a circlip 67 abutting the inner bush 68 of the lower bearing 
72. The shaft 16 is urged in a downward direction by a compression spring 
69 which extends between the circlip 67 and the bottom of the gear 66. 
Upward movement of the shaft 16 relative to the housing 46 is therefore 
limited by full compression of the spring 69. The shaft 16 is constrained 
to linear upward and downward movement by the bush 68 and an upper bush 
70. 
Linear motion monitoring means 36 are constituted by a permanent magnet 71a 
sandwiched between two pole pieces 71b and 71c, fixed to the upper end of 
the shaft 16, and a Hall effect device 71d fixed to the housing 46 at a 
position thereof adjacent to the position at the centre of available 
travel of the magnet 71a relative to the housing 46. 
The motor driver amplifier 30 and the computer controller 28 are positioned 
adjacent to the housing 46, with the motor driver amplifier 30 connected 
to the outside power supply and the computer controller 28 connected by an 
RS232 line (not shown) to an outside computer. 
In FIG. 5 there is illustrated a block diagram of the controller 28. In the 
controller 28, a clock 82 sends time signals to a central processing unit 
84. The central processing unit 84 sends and receives data via a data bus 
86 and sends instructions under control of an address bus 88. The address 
bus 88 and data bus 86 are both connected respectively to: 
1) a digital input/output 90, which receives initial signals and outputs 
signals which control an air valve supplying the chuck; 
2) an analogue to digital input 92, which receives signals relating to 
motor current which varies between 0 and 10 V; 
3) a digital to analogue output 94 which gives out signals that control the 
applied torque and the motor angular velocity, both outputs being in the 
range 0 to 10 V; 
4) a program memory 96, which is a read only memory containing program 
data; and 
5) a serial communication port 98, which receives instructions from the 
operator and outputs results to information display or storage means, eg. 
printer or visual display unit, or computer system, via a cable connection 
using RS232 protocols. 
In FIG. 6 the circuit diagram of the motor driver 30 is shown. The motor 20 
is connected to a MOSFET transistor quadrature bridge arrangement, 208, of 
the motor driver 30, configured such that the motor may be energised in 
the forward or backward direction by selective switching on or off of the 
MOSFET transistors of the arrangement 208. 
A CMOS logic inverter arrangement 216 is connected to the gates of the 
transistors of the arrangement 208 so as to switch the MOSFET transistors 
fully on or fully off in such a way that the motor is fully energised in 
the forward direction or reverse direction only, as required. 
A logical AND gate plus a logical inverter arrangement 214 is connected to 
pass the control square wave signal to the inverter arrangement 216. A 
reverse digital input 220 derived from the computer controller 28 
determines whether that signal passes to the forward or the reverse MOSFET 
transistors of the arrangement 208. 
Two logical inverters 200 are connected with positive feed back components 
to produce a square wave signal. This signal is fed to an operational 
amplifier 202 connected with negative feedback via a capacitor arranged as 
an integrating circuit. This arrangement provides an output that is the 
mathematical integral of the input square wave, and is therefore described 
as a triangular wave that repeatedly changes from zero to maximum 
linearly, and then immediately from maximum to zero linearly. 
The triangular wave is fed to an operational amplifier 212 which is 
configured as an analogue comparator. The output of the operational 
amplifier 212 will be maximum (described as duty on) when the 
instantaneous input voltage from the operational amplifier 210 is greater 
than the triangular wave instantaneous voltage. Conversely the output of 
the operational amplifier 212 will be zero (described as duty off) when 
the instantaneous input voltage from operational amplifier 210 is less 
than the triangular wave instantaneous voltage. It follows that the higher 
the input voltage to the comparator 212 from operational amplifier 210, 
then the ratio of duty on time to duty off time will change linearly from 
0% to 100% as the input voltage from the operational amplifier 210 moves 
from zero to maximum. 
The shaft encoder 26 is connected to a proprietary frequency-to-voltage 
converter 204 which is arranged to produce a voltage output according to 
motor speed. This speed derived signal is fed to the inverting input of 
the operational amplifier 210. A speed control input to the system 228 is 
connected externally to the computer controller 28, and internally of the 
motor driver 30 to the non-inverting input of the operational amplifier 
210. The output of the operational amplifier 210 is thus proportional to 
the difference between the speed control voltage from the input 228 and 
the motor speed derived voltage from the converter 204. Thus the motor 
speed may be controlled within a closed loop arrangement. 
A low value resistor 230 is connected in series with the motor 20 such that 
all motor current passes through it in a positive sense, regardless of the 
direction of rotation of the motor. This resistor will develop a voltage 
across it in proportion to the current flowing through the motor. This 
voltage is applied to an operational amplifier 206, which is arranged to 
amplify the voltage to a value in the zero to maximum range for the 
required motor current. 
This current derived voltage is passed to the computer controller 28 for 
external processing via the terminal 222, and also to an inverting input 
of the operational amplifier 218. Thus the motor torque is controlled 
within a closed loop arrangement. 
A torque demand current input 226 from the computer controller 28 is 
connected to the non-inverting input of the operational amplifier 218. The 
operational amplifier is thus configured to produce an output proportional 
to the difference between the torque demand voltage and the motor current 
derived voltage from the amplifier 206. 
The motor shaft encoder 26 output is made available to the computer 
controller 28 via a connection 224 to enable positional control 
arrangements. 
Analogue control of the motor in the forward and reverse direction is 
achieved by changing the duty cycle of a square wave signal such that the 
ratio of motor on time to motor off time is infinitely variable. This 
cycling of the on to off state is carried out typically at 20 kHz, and 
this frequency is orders of magnitude faster than the mechanical time 
constants of the motor assembly. Thus the motor operates according to the 
average voltage or current applied. 
FIG. 7 shows a flow diagram of how the computer controller 28 is programmed 
and thus how the above described capping machine works. The first step 300 
is to load a new cap into the chuck 18 from the cap transfer arm 38. In 
the step 302 the jaws 62 of the chuck heads 56 close gripping the cap 40. 
The chuck 18 is then lowered in step 304 onto the container 10. When the 
chuck 18 makes contact with the container 10 the capping sequence is 
started in step 306. Initially the chuck head 56 rotates against the 
screw-on sense of the thread of the container at a slow angular velocity 
in step 308. As the cap is rotated the vertical movement sensor 36 looks 
for a level fall in the vertical position of the chuck 18. The vertical 
movement sensor 36 is then seen to constitute screwthread-disengagement 
monitoring means. In step 310 this rotation is continued until the start 
of the thread is thus detected. Once this has been detected the computer 
controller 28 then sets the motor torque to maximum in step 312 and the 
angular velocity of the chuck to high in the opposite sense (the screw-on 
sense of the thread on the containers' 10 neck) in step 34. 
The motor shaft encoder 26 then checks the angle that the chuck has rotated 
in step 316. If it has reached x.degree., which is the free thread angle 
on the container neck (this will have been predetermined and loaded into 
the computer controller 28), then the chuck 18 proceeds onto the next step 
322 in the capping process. If the angle reached is not x.degree., then in 
step 318 the controller 28 checks whether the chuck 18 has stalled. If it 
has not, rotation is continued and step 316 continued with. 
If the chuck has stalled then in step 320 the controller 28 rejects the 
capping as having an incorrect angle, possibly due to a bad thread on 
either the cap 40 or the container 10 and proceeds to the stop step of the 
capping processing. 
In step 322 the torque applied by chuck 18 is set to a pre-determined 
torque T1. The chuck 18 in step 324 is then advanced very slowly in the 
same sense as in step 314. In step 326 torque is applied by the chuck 18 
for a set time and is measured. If this measured torque Tm is greater than 
or equal to the predetermined torque T1 then the next step is step 334. If 
the torque measured Tm is not greater than torque T1 then step 328 
follows, in which the computer controller 28 checks whether the maximum 
time taken to tighten the cap has been exceeded. If it has the computer 
controller 28 rejects that particular capping as bad torque in step 330 
and the capping process is stopped. If the time is not exceeded then in 
step 332 the measured torque is compared with a predetermined overtorque 
value T2. If it is exceeded then step 330 follows as above, otherwise the 
tightening of the cap is continued in step 326. 
In step 334 after the correct torque has been applied the chuck 18 is 
stopped. Step 336 allows a delay of 30 mS to allow the component parts of 
the container and cap 18 to settle. In step 338 the rotation of the chuck 
18 is reversed and the torque applied by the chuck 18 is set to a value 
where the set torque T1 is multiplied by a torque test factor y, in order 
to carry a twist-off test to test whether the cap 40 is screwed on 
satisfactorily. 
Step 340 allows a delay of 50 mS to allow the container components to 
settle. In step 342 the motor shaft encoder 26 then checks what angle of 
rotation has been achieved by the chuck 18. If this angle is greater than 
the reverse test limit Z.degree. then the capping is rejected as a 
twist-off fail by step 344. If the test in step 342 is passed then the 
capping machine proceeds to the end of the capping process. In step 346 
the chuck 18 stops, in step 348 the chuck 18 is released and then raised 
in step 350. 
FIG. 8 shows graphs of the angular velocity of the chuck and the torque 
applied by the chuck. In Part A of the graph which corresponds to the slow 
reverse of the chuck seeking the thread it can be seen that the torque and 
angular velocity remain approximately constant until there is a blip in 
the torque as the start of thread is found owing to the chuck dropping and 
the need for more torque to maintain the chuck's angular velocity and then 
reverse torque to change the direction of the chuck. In section B the 
chuck is moving fast forward for x.degree. to screw on the cap. This 
results in a large peak for angular velocity and a sharp positive peak for 
torque as the chuck angular velocities up and sharp negative peak for 
torque as the chuck is slowed. Section C shows the period while the cap is 
tightened. In this section angular velocity remains constant and torque 
slowly increases. In section D the chuck 18 dwells while the container 
parts are settled and thus there is a decrease in angular velocity and 
torque to zero as the chuck stops. In section E the chuck is applying 
reverse twist-off which results in a negative peak for torque which is 
maintained and a negative blip on angular velocity as some movement occurs 
and then the cap holds. There is then a positive peak on torque as the 
torque is reversed to let off the torque applied by the chuck 18. 
FIG. 9 shows non-inertial reactionary torque to which the chuck is 
subjected to by the cap as a function of the angle through which the cap 
has been rotated beyond the start-of-thread position. Any curve within the 
two illustrated curves in FIG. 10 is acceptable. Otherwise, if the curve 
lies outside that window, the cap and its associated container will be 
rejected. 
Numerous modifications and variations to the illustrated capping machine 
will readily occur to a reader of normal skill in the art without taking 
the resulting construction outside the scope of the present invention. For 
instance the vertical movement sensor 36 could be dispensed with and the 
torque sensor used instead to detect the start of the screw-thread. 
The motor drive 30 may be replaced by a proprietary servo-amplifier type 
No. SSA-8/80 manufactured by Elmo Motion Control Limited, of Petah Tikva, 
Israel. 
Whilst the accompanying drawings illustrate a single spline machine with a 
single chuck, it will be appreciated that it could be modified to have two 
or more splines with respective chucks, each at the same stage in the 
capping procedure at any given moment, or each at respective different 
stages in the capping procedure at any given moment. 
Step 322 in FIG. 7 may involve the reversal of the torque applied to the 
chuck by the motor 20, in which case the angle x.degree. may be half the 
free thread angle on the container neck, so that the rotary speed of the 
chuck is ramped up and ramped down and is thus triangular as a function of 
time.