Sheet metal container making – Apparatus applying closure to receptacle
Reexamination Certificate
2000-12-11
2003-06-10
Bray, W. Donald (Department: 3725)
Sheet metal container making
Apparatus applying closure to receptacle
C072S019700, C072S021400, C072S031040, C413S020000, C413S030000
Reexamination Certificate
active
06575683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the seaming of containers such as cans of foodstuffs or the like by means of a seaming machine in which the application of the seaming tool (usually a wheel) on the lip to be seamed is controlled by the rolling of a follower against a cam formed by an annulus, formed on an active sector of which is an external profile comprising an ascending ramp and a descending ramp.
2. Description of the Prior Art
The production and/or use of cans of foodstuffs necessitates one or two operations of seaming of the can ends. The tightness of a closed can depends on how tight the seams are on the inside.
In two-pass seaming machines, this tightness is closely related to the force applied to the metal sheets forming the can and the can end during the second pass. There are two methods of monitoring the quality of the seaming by real-time measurement of the force applied by the cam to the follower actuating the seaming wheel.
The first method, illustrated in document U.S. Pat. No. 4,205,617 A, utilizes force sensors, which seem to be load cells, incorporated in the cam, which has a solid active zone, and connected to an appropriate signal processing circuit, but there is no description given of how they are incorporated, and there are reasons for thinking that the way the sensors are implanted greatly influences the results of the measurements and their reliability.
The second method is used by a commercially available two-pass seaming driving cam, in which the cam corresponding to the second pass comprises in the active sector, internally, a profile defined by two deep symmetrical recesses with rounded corners, containing not load cells but deformation gauges, whose electrical output signals are processed by an analytical device to produce a signal representing the force exerted by the cam on the follower, in practice a signal proportional to this force. Such an arrangement is also shown in documents WO 98/07 534 and EP 0 181 234. To the best of the Applicant's knowledge, these two recesses are machined in the thickness of the cam, on the opposite side from the active profile, their form being defined only as a function of the constraints of the installation of the gauges.
Research carried out by the Applicant has shown that this arrangement is not entirely satisfactory in the sense that the electrical signal obtained does not faithfully represent the force applied by the cam in bringing about the seaming. Although, as expected, a sensitive part does exist in the active zone of the profile, it is found that when a constant force travels from one end of the sensitive part to the other, the response of the sensor is not constant, which is undesirable. The response is at its greatest when the force is in the middle and at its lowest when the force is at either end. The ratio of non-uniformity may be as much as 50% or more—which means that when the force is in the middle, the response of the system may be more than twice what it is when the force is at either end.
SUMMARY OF THE INVENTION
The object of the invention is to provide a solution to the faults of the two methods and to provide a cam, or a modification of an existing cam, that has a better response all the way along the length of the sensitive part.
The object of the invention is achieved with a seaming driving cam formed by an annulus, formed on an active sector of which are, on the one hand, an external profile comprising an ascending ramp and a descending ramp and, on the other hand, an internal profile defining a plateau zone between two deep recesses, sensors being arranged so that their electrical output signals are processed by an analytical device to produce a signal representing the force exerted by the cam on a drive follower that rolls on it, the cam being characterized in that the sensors are load cells arranged between the plateau zone and an adjustable bearing part that sits in front of it and that is fixed to an inactive part of the cam. The thickness of the bridges of material left by the deep recesses is such that their stiffness is negligible compared with the stiffness of the sensors. The rigid bearing part provides an alternative active zone of low deformability comparable with the virtually nondeformable solid active zone of the first method, in contrast to the conventional active zone with an internal plateau profile as in the second method. In one particular embodiment of the invention, it has been possible to define the different components so that the extra deflection under the seaming force of the cam profile in its active part compared with the deflection of the solid cam of the first method is not more than two hundredths of a millimetre. The load cells are advantageously quartz discs and are prestressed; their very high coefficient of stiffness (several hundreds of millions of daN per meter) is compatible with the minimum deflection defined above.
The cam according to the invention can easily be produced by modifying an existing cam, especially if it already includes a plateau zone. Tapped holes are machined in the base of the cam to enable the sensor bearing part to be mounted using screws, advantageously combined with a system of adjustment by means of eccentrics.
This adjustment system both enables the sensors to be prestressed and allows the cam profile to be slightly predeformed in the opposite direction to the deformation that will occur as the follower passes over it. Besides reducing the effects of the deformation of the system under load, this operation eliminates the microshocks of contact between the parts during operation and thus eliminates wear due to friction (“fretting corrosion”).
Other characteristics and advantages of the present invention will be found in the following description of an example of an embodiment of the invention illustrated in the accompanying drawings.
REFERENCES:
patent: 3222921 (1965-12-01), Schreiber et al.
patent: 4022141 (1977-05-01), Bartenstein
patent: 4205617 (1980-06-01), Chmielowiec
patent: 4606205 (1986-08-01), Segredo et al.
patent: 0 181 234 (1986-05-01), None
patent: WO 98/07534 (1998-02-01), None
Bray W. Donald
Centre Technique des Industries Mecaniques
Hoffmann & Baron , LLP
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