CA1061190A

CA1061190A - Production of closed bottom shells

Info

Publication number: CA1061190A
Application number: CA314,984A
Authority: CA
Inventors: Frederick G. Kudert; Harold C. Lemke; Vance B. Gold; Harold J. Jessogne; Bengt S. Backe; William D. Timmins; Edward F. Kubacki
Original assignee: American Can Co
Current assignee: Primerica Inc
Priority date: 1975-03-17
Filing date: 1978-10-31
Publication date: 1979-08-28

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention provides in a machine which forms shells of can dimension from a blank by moving the blank through a deforming means including a die and in which the blank is of a material having given electromagnetic properties, the combina-tion of (a) a punch of material having different electromagnetic properties, on which the shell is supported on emerging from the deforming means, (b) an electromagnetic field sensor positioned to create an electromagnetic field in an area corresponding to the free end of a shell of correct length, and (c) means to dis-criminate between the field altered by the punch element alone, not supporting a shell of correct length, and the field altered by a shell of correct length on the punch.

Description

~8i6~
The present invention relates to machines which form shells of can dimensions.
This application is a divisional application of copending Canadian application l~o. 245,507 filed Feb. 11, 1976 to which reference may be made for a full discussion of the background to the present invention~ Attention is also directed to our copending application Nos. filed on even date therewith.
In said copending application No. 245,507 there is dis-, closed and claimed a machine for producing elongated shells of can dimension and comprising (a) die means at a forming station to produce an elongated shell from a cup or shorter length; (b) a punch assembly afforded by a punch member'and a complemented stripper member, coupled one to another both for unitary forward movement into and through the die forming station to form the sheel from the cup and for retracting movement of the punch mem-ber independently of the stripper member which is to be held stationary after the shell is formed, said stripper member in ¦
its stationary state stripping the shell while said punch mem-ber is being rétracted, and said ~tripper member having a piston thereon disposed in a cylinder presented by the punch assembly;
(c) a fixed bushing for supporting and guiding said punch assembly and having a chamber for receiving and transmitting fluid under pressure to said cylinder to hold said stripper member stationary at the end of forward travel, said punch assembly being provided with a transfer port communicating with said cylinder and so located as to traverse said bushing chamber over a path of predetermined extent during reverse movement f said punch member whereby fluid under pressure in said bushing chamber may be communicated to said cylinder at the end of for- r ward punch travel and allowed to prevail until said port clears the bushing chamber to depressurize the latter during reverse movement of said punch member; and (d) means to retrac-t the stripper member after said point has so cleared the bushing chamber.
According to the present invention there is provided in a machine which forms shells of can dimension from a blank by moving the blank through a deforming means including a die and in which the blank is of a material having given electromagnetic properties, the combination of (a) a punch of material having different electromagnetic properties, on which the shell is 1~ supported on emerging from the deforming means, (b) an electro-magnetic field sensor positioned to create an electromagnetic field in an area corresponding to the free end of a shell of correct length, and (c) means to discriminate between the field altered by the punch element alone, not supporting a shell of correct length, and the field altered by a shell of correct length on the punch.
The present invention will be described with reference to the accompanying drawings in which:
Figures 1, 2 and 3, are detail views of a short shell detector means embodying the present invention.
The short shell detector embodying the invention is incorporated in a machine as described in siad copending applica-tions, to which reference should be made for a full description of the details of machine construction, operation and control.
In the instance of thin-walled shells, a proximity detector, physically contacting the shell to determine correct length, is not always reliable and in addition requires consid-erable maintenance. What is more, physical contact can result in a damaged shell, necessitating shutdown.
The short shell detector 68 embodied in the present machine operates by detec-ting metallurgical differences in materials based on changes in an electromagnetic field and 1~61~

emitting a corresponding signal. In one specific form, it includes an oscillator having an operating frequency which depends upon the inductance of a particular sensing coil If one substance interdicts the field of the coil, the inductance will be of a particular value, but if another substance of markedly different magnetic properties interdicts the field the inductance will be of different value.
~ eferring to Fig. 1 the short shell detector com-prises an inductor 250, represented by a core 251 and a coil 252, that is connected into the frequency-determining circuit of an oscillator 254. A phase-locked-loop frequency comparator 255 is coupled to the oscillator 254.
The inductance of coil 252 will vary, depending upon whether there is merely an air gap beneath the coil, whether there is only the punch element 35L (tungsten carbide) adjacent the coil, or whether the steel shell 26 projects into the field space at the end of the coil.
In the null state, with neither a punch nor a shell in the inductance field, Fig. 1 the fre~uency of the oscillator 254 may be taken as a value fO, significant of an air gap.
An event-se~-point switch in the machine's logic con-trol is electrically triggered at the time when shell formation of correct length should have taken place. The sensing probe, the inductance 250, is located to sense whether a shell of correct length has been obtained; if this is indeed the case, Fig. 2, the variance in the inductance results in an oscillator frequency fl, Fig. 2. The output from the phase-locked-loop, delivered to -the logic control, signifies "no error".
On the other l~and, the inductance of the sensing coil 252 will be different if, at the time of event-set-point switch-ing, only the material of the punch element interdicts the inductance field, resulting in a frequency f2 emitted by the ~6~L~IIL9~

oscillator, Fig. 3. This frequency is detected by the internal comparator of the phase-locked-loop; the output characterizes an error. The logic control, informed of the error, signals the appropriate servo valves, which thereupon set the main cylinder valve and the cup feeder valves of the machine to null position.
In the illustrated short shell detector, f2~ fo> f and the differences between the sensor frequencies can readily be made great enough for consistent and accurate detection in the comparator 255. It will be recognized that other frequency relations may obtain if the magnetic properties of the punch and shell are changed (e.g., an aluminium shell on a steel punch) or if the sensor is modified to constitute a capacitive sensing device instead of an inductive device.
Similar event-set-point switching in the logic control is employed for the various "no error" machine functions: cup feed rod fully extended; cup in position; punch body fully extended; shell being stripped and so on.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a machine which forms shells of can dimension from a blank by moving the blank through a deforming means including a die and in which the blank is of a material having given electromagnetic properties, the combination of (a) a punch of material having different electromagnetic properties, on which the shell is supported on emerging from the deforming means, (b) an electromagnetic field sensor positioned to create an electromagnetic field in an area corresponding to the free end of a shell of correct length, and (c) means to discriminate between the field altered by the punch element alone, not suppor-ting a shell of correct length, and the field altered by a shell of correct length on the punch.

2. The combination of claim 1, in which the field sensor is an inductance connected in the frequency-determining circuit of an oscillator.

3. The combination of claim 1 or 2 in which the discriminating means includes a phase locked loop comparator coupled to the oscillator, the comparator discriminating between an air-gap frequency, a frequency where the shell is of correct length, and a frequency where the shell is short.