PROCESS MONITORING OF MOLDED CLOSURES

Field of the Invention

[0001] The present invention generally relates to process monitoring of

molded closures. In particular, the invention relates to an apparatus and method for

monitoring molded closures after manufacture of the closures.

Background of the Invention

[0002] A rotary compression molding apparatus is typically employed for

the manufacture of molded plastic closures. A rotary turret carries multiple, vertically

oriented tool assemblies which are rotated by the turret relative to upper and lower fixed

cams. Rotary motion of the tooling relatively moves respective sets of upper and lower

or, male and female, mold assemblies. As the turret rotates, a metered charge of molten

plastic is placed into each open female mold, and the male and female molds relatively

move to compress the molten plastic therebetween to form the closure. Liquid cooling

within the tooling promotes rapid plastic solidification. The molding cycle is completed

by relative movement of the tooling to open the mold cavity, and eject the molded

closure.

[0003] Quality monitoring or inspection techniques employed after

compression molding have necessarily resulted in a lag time between identification of

molding problems and their correction. By one inspection technique, molded closures are

sampled, and carefully measured. As a result of the time lag between identification of a

problem and its correction, many unacceptable closures may be produced. It is also

possible that poor quality closures can be manufactured between the times at which

samples are taken. Additionally, the detection of a poor quality closure does not

necessarily identify the specific problem that resulted in its formation, thus requiring

secondary measurements and process experiments to determine the cause of the faults.

Examples of secondary measurements and process experiments would be dimensional

measurements obtained from a coordinate measuring machine or a caliper.

[0004] Another technique for inspecting molded closure parts employs a

vision-based inspection system, which visually inspect either periodic closure samples, or

100% of the closures being molded. However, these systems have proven to be

expensive to implement in connection with high speed production, which may entail

hundreds of closures per minute. Such vision-based systems are sensitive to the

background lighting of the room that the apparatus is in and process lighting angles.

While the time lag between manufacturing and inspection is minimal, detection of poor

quality closures does not give specific information regarding the cause of the problem.

[0005] An inspection or monitoring system is needed wherein measurement

of molded closures can be effected on an on-line basis as they are ejected from an

associated compression molding apparatus. The testing would be conducted in a fashion

such that each individual closure can be associated with a particular one of the mold

tooling sets of the molding apparatus. Problems associated with the specific tool set can

thus be readily identified. Furthermore, by monitoring specific parameters, specific sub¬

systems and process settings of the molding apparatus could be modified. For example,

temperature measurement of each closure correlates to dimensional shifts, quality shifts,

and cooling system performance. Measurement of top panel thickness correlates directly

to closure weight and final dimensions. Warpage indicators or the concavity of the

closure top surface, correlate directly to cooling flow and plastic melt temperature.

[0006] Combinations of measurements' behavior would allow technicians to

quickly diagnose a problem and point to a sub-system of the molder, or individual tool

that would require maintenance or adjustment. Because the measurements would be

variables, rather than attributes, they would lend themselves to control charting, and

would indicate processes that were changing, thus giving early warning of changing

processes and allowing maintenance and adjustment to be performed before scrap is

produced. This would be in direct distinction from the previous methods, which are only

triggered when scrap is produced.

[0007] The primary object of the present invention is to provide a method

and apparatus for monitoring molded closures that would measure specific parameters of

the closure so that problems with specific tool sets, sub-systems, and process settings of

the molding apparatus could be identified, thus substantially reducing the amount of scrap

that is produced.

Summary of the Invention

[0008] The present invention is directed to an apparatus and method for

monitoring molded plastic closures after manufacture of the closures. The method

comprises passing the closures above an infrared sensor and measuring the temperature of

the top panel of the closures, passing the closure above a first laser and measuring the

concavity of the top panel, passing the closure under a second laser and measuring the

location of the inside surface of the top panel, obtaining the thickness of the top panel by

subtracting the concavity of the top panel from the location of the inside surface of the

top panel, and approving or rejecting the closure. The infrared sensor measures the

temperature of the top panel by emitting an infrared beam, preferably having a

wavelength between about 8 to about 14 microns, onto the top panel surface and

collecting the intensity of the beam reflectance from it. The first and second lasers

measure the concavity and the location of the inside surface of the top panel by emitting a

laser beam, preferably having a wavelength that is about 670 nanometers, onto the outside

and inside surface of the top panel and collecting the distance between these surfaces and

the laser face. The closures are approved or rejected by analyzing the measurements of

the infrared sensor and the first and second lasers with a data acquisition control system

that is connected to the infrared sensor and the first and second lasers. The measurements

are then presented on a graphical user interface.

[0009] The apparatus comprises an aluminum coated platform having an

aluminum-coated supporting structure and a pocketwheel having pockets, a closure

feeding means for feeding the closure to the pocketwheel, and a closure receiving means

for receiving the closure after the closure is discharged from the pocketwheel. The

closure feeding means and closure receiving means are preferably also pocketwheels

having pockets for holding the closures. The pockets for the closure feeding

pocketwheel, pocketwheel, and closure receiving pocketwheel are preferably 30 mm in

diameter. The pocketwheel is radially oriented from the closure feeding pocketwheel and

the closure receiving pocketwheel is radially oriented from the pocketwheel and across

from the closure feeding pocketwheel. The pocketwheel, closure feeding pocketwheel,

and closure receiving pocketwheel are connected to the platform via coupling means,

preferably gears that have a motor coupled to them and allow the gears to transfer motion

to the pocketwheels. The closure feeding pocketwheel and the closure receiving

pocketwheel move in a direction opposite the pocketwheel. In addition, the infrared

sensor is coupled to the platform and the first and second lasers, respectively positioned

below and above the platform, are coupled to the supporting structure.

[0010] In operation, the closure feeding pocketwheel accepts the closure

from a molding apparatus and passes the closure to the pocketwheel. The pocketwheel

passes the closure above the infrared sensor and the first laser and below the second laser,

with the sensors and the lasers each measuring a parameter of the closure for approval or

rejection. The pocketwheel passes the approved closures to the closure receiving

pocketwheel, which clears these closures from the platform. The rejected closures are

cleared from the platform by an airway situated on the side of the platform. The platform

includes an aperture to receive the infrared beam from the infrared sensor and a slot to

receive the laser beam from the first laser. The aperture is about a quarter inch in

diameter and the slot is about an eighth inch in width and one inch in length. The closure

feeding pocketwheel, preferably made of high density polyethylene, and the closure

receiving pocketwheel, preferably made of coated aluminum, are about four and one-half

inches in diameter. The pocketwheel, preferably made of coated aluminum, is about

seven inches in diameter.

Brief Description of the Drawings

[0011] Figure 1 is a perspective view of the closure monitor apparatus.

[0012] Figure 2 is a top view of the closure monitor apparatus.

[0013] Figure 3 is a bottom view of the closure monitor apparatus.

[0014] Figure 4 is a back view of the closure monitor apparatus.

Detailed Description of Preferred Embodiments

[0015] Figure 1 shows a perspective view of the closure monitor apparatus

10 of the invention. The apparatus 10 comprises a platform 11 having a supporting

structure 12 and a pocketwheel 14, a closure feeding means 13 for feeding the closure to

the pocketwheel 14, and a closure receiving means 15 for receiving the closure after the

closure is discharged from the pocketwheel 14, each of which are coupled to the platform

11. For the purposes of this preferred embodiment, the closure feeding means 13 and

closure receiving means 15 each comprise a pocketwheel. However, other means that

would properly feed and receive the closures to and from the pocketwheel 14, such as

conveyor belts, could be used. The platform 11 and the supporting structure 12 are both

made from metal, preferably coated aluminum. Together, the platform and supporting

structure are about fifteen inches wide and ten inches high. The pocketwheels 13, 14, 15

each have pockets 23 for housing a closure during the monitoring process and are situated

so that the pocketwheel 14 is radially oriented from the closure feeding pocketwheel 13

and the closure receiving pocketwheel 15 is radially oriented from the pocketwheel 14

and across from the closure feeding pocketwheel 13. The closure feeding pocketwheel

and closure receiving pocketwheel 13,15 are about four and a half inches in diameter and

the pocketwheel 14 is about seven inches in diameter. The pockets 23 for the

pocketwheels 13, 14, 15 are about thirty millimeters in diameter. In addition, the closure

feeding pocketwheel 13 comprises plastic, preferably high definition polyethylene, and

the pocketwheel and closure receiving pocketwheel 14,15 comprise metal, preferably

coated aluminum. Pocketwheels comprised of aluminum leave marks on the closure and

therefore contaminate the closure. Therefore, the pocketwheel and closure receiving

pocketwheel 14, 15 are comprised of coated aluminum to substantially reduce the number

of marks left on the closure. As will be described below, during the monitoring process,

the closure feeding pocketwheel 13 accepts a closure from a molding apparatus. During

this time, the possibility exists for the closure feeding pocketwheel 13 and the molding

apparatus to collide and cause damage to the tooling for the molding apparatus. If the

closure feeding pocketwheel 13 is comprised of plastic, which is softer than other

materials such as coated aluminum, then damage to the tooling will be substantially

reduced.

[0016] The apparatus 10 also comprises an infrared sensor (Fig. 3, 16) that

is coupled to the platform 11, a first laser (Fig. 3, 18) that is coupled to the supporting

structure 12 and situated below the platform 11 and under the pocketwheel 14, and a

second laser 17 that is also coupled to the supporting structure 12 and situated above the

pocketwheel 14. For the purposes of this invention, the infrared sensor (Fig. 3, 16) is

preferably a high speed infrared sensor and the lasers (Fig. 3, 18), 17 are preferably

visible red semiconductor lasers. The infrared sensor used in this invention was

manufactured by Everest Interscience Incorporated and the lasers, each being Part No.

LK031 , were manufactured by Keyence Inc. The infrared sensor (Fig. 3, 16) and the

lasers (Fig. 3, 18), 17 are coupled to the platform 11 and the supporting structure 12 via a

coupling means 24 such as clamps, screws, fasteners, or a nut and bolt combination. The

coupling means 24 preferably are constructed from aluminum or steel material, however

the coupling means 24 may be constructed from any metal, metal alloy, or nonmetal that

would provide rigid structural support . The closure feeding pocketwheel, pocketwheel,

and closure receiving pocketwheel 13,14,15 are coupled to the platform 11 via coupling

means, preferably gears (Figs. 3 and 4, 26), that are mounted on the closure feeding

pocketwheel, pocketwheel, and closure receiving pocketwheel 13,14,15 and are housed

below the platform 11. The gears (Figs. 3 and 4, 26) transfer motion to the pocketwheels

13,14,15 from a motor 19 that is coupled to the gears (Figs. 3 and 4, 26) and the

supporting structure 12. The motor (Fig. 4, 19) is coupled to the gears (Figs. 3 and 4, 26)

and the supporting structure 12 via a coupling means 24 such as clamps, screws,

fasteners, or a nut and bolt combination. The coupling means 24 preferably are

constructed from aluminum or steel material, however the coupling means 24 may be

constructed from any metal, metal alloy, or nonmetal that would provide rigid structural

support. For the purposes of this invention, common spur gears were used and the motor

19 is a servomotor. The closure feeding pocketwheel and closure receiving pocketwheel

13,15 move in a direction opposite to the direction the pocketwheel 14 moves.

Specifically, the closure feeding pocketwheel and closure receiving pocketwheel 13,15

move in a clockwise direction and the pocketwheel 14 moves in a counterclockwise

direction.

[0017] During the monitoring process, the closure feeding pocketwheel 13

accepts a plastic closure, with the plastic closure being upside down, from a molding

apparatus that is situated above the monitoring apparatus 10 and beside the closure

feeding pocketwheel 13. The closure is then passed from the closure feeding pocketwhel

13 to the pocketwheel 14. The pocketwheel 14 passes the closure above the infrared

sensor (Fig. 3, 16) and the first laser (Fig. 3, 18) and below the second laser 17. The

infrared sensor (Fig. 3, 16) measures the temperature of the top panel of the closure by

emitting an infrared beam onto the top panel and collecting the intensity of the beam

reflectance from it. The infrared beam is emitted through an aperture (Fig. 2, 20) on the

platform 11 and has a wavelength that is between about 8 to about 14 microns. The

aperture (Fig. 2, 20) is about a quarter inch in diameter. The first and second lasers (Fig.

3, 18,), 17 measure the concavity and the location of the inside surface of the top panel

respectively by emitting a laser beam onto the outside and inside surfaces of the top panel

and collecting the distance from these surfaces to the laser face. For the purposes of this

invention, concavity means the maximum depth of the top panel curvature that is

observed in the center of the closure top panel. The distance from the outside and inside

surfaces of the top panel is measured using the triangulation measurement system. The

lasers use a Charged Coupled Device (CCD) array as a light receiving element. The light

reflected by the outside and inside surfaces passes through a receiver lens that focuses the

light on the CCD. The CCD detects the peak value, or the brightest point, of the light

quantity distribution of the laser beam spot and identifies this as the target position on the

inside and outside surfaces of the top panel. The thickness of the top panel is then

obtained by subtracting the concavity of the top panel from the location of the inside

surface of the top panel.

[0018] The laser beam from the first laser (Fig. 3, 18) is emitted through a

slot (Fig. 2, 21) in the platform 11. Each of the laser beams from the first and second

lasers (Fig. 3, 18), 17 have a wavelength that is about 670 nanometers . The slot (Fig. 2,

21) has a width of about one eighth inch and a length of about one inch. The calculation

of the measurements can be performed either manually or electronically, but for the

purposes of this invention the calculations were performed electronically by a data

acquisition control system that is coupled to the infrared sensor (Fig. 3, 16) and lasers

(Fig. 3, 18), 17 via electrical wires 25. The control system, which drives the servomotor

and synchronizes it to the molding machine rotation, is manufactured from Alan Bradley

Programmable Logic Control (PLC) components and proprietary software. After the

measurements are performed, the closure is passed from the pocketwheel 14 to the

closure receiving pocketwheel 15. Based on the measurements, the closures are either

approved or rejected. The closure receiving pocketwheel 15 passes approved closures to

a passageway 22 made for collecting the closures. The passageway 22 is coupled to the

platform H ₅ is situated next to the closure receiving pocketwheel 15, and comprises

stainless steel. Rejected closures are cleared from the closure receiving pocketwheel 15

and platform 11 by an airway 27 on the side of the platform 11 below the closure

receiving pocketwheel 15. The airway 27 comprises an aperture that is about 0.03 inches

in diameter and blows the rejected closure into a chute (not shown) that leads the rejected

closure into a scrap box (not shown).

[0019] Temperature measurement of each closure, by the infrared sensor

(Fig. 3, 16), correlates to dimensional shifts, quality shifts, and cooling system

performance. Measurement of top panel thickness, by a combination of the

measurements of the first and second lasers (Fig. 3,18), 17 correlates directly to closure

weight and final dimensions. Warpage indicators or the concavity of the closure top

surface, as measured by the first laser (Fig. 3,18), correlates directly to cooling flow and

plastic melt temperature. Combinations of measurements' behavior allow technicians to

quickly diagnose a problem and point to a sub-system of the molder, or individual tool

that requires maintenance or adjustment. Because the measurements are variables, rather

than attributes, they lend themselves to control charting, and indicate processes that are

changing, thus giving early warning of changing processes and allowing maintenance and

adjustment to be performed before scrap is produced. For the purposes of this invention,

the process moves at a speed that is equal to the speed of the production flow, which is

about 500-600 with the capacity of 1200 parts/minute.

[0020] Having described the presently preferred embodiments, it is to be

understood that the invention may be otherwise embodied within the scope of the

appended claims.