The invention relates to methods and apparatus for regulating the permeability of wrappers of plain or filter cigarettes, cigars, cigarillos, filter rod sections and like rod-shaped articles of the tobacco processing industry. More particularly, the invention relates to improvements in methods of and apparatus for regulating the permeability of wrappers of rod-shaped articles of the tobacco processing industry (hereinafter called cigarettes for short) whose fillers are formed from fibrous material the filling power of which is monitored in order to maintain the hardness of the fillers at a constant value. The fibrous material can constitute natural, reconstituted or artificial tobacco (which may but need not contain nicotine) and/or filter material.
In the manufacture of cigarettes, fibrous material (hereinafter called tobacco for the sake of convenience and simplicity) is continuously gathered into a thin layer which is converted into a narrow stream. The stream is equalized to be converted into a rod-like filler which is thereupon condensed and is simultaneously draped into cigarette paper or other suitable wrapping material in a wrapping mechanism to form a rod which is severed at desired intervals to yield a succession of cigarettes of unit length or multiple unit length. The equalizing operation normally involves removing from the stream the surplus of fibrous material in accordance with the measurement of the mass flow (quantity or mass per unit length of the filler) by a monitoring device which can include a source of corpuscular radiation (e.g., beta rays) and an ionization chamber. A cigarette making machine which operates in the just described manner is manufactured by the assignee of the present application and is known as PROTOS. The distributor unit of the PROTOS machine is described in the commonly owned U.S. Pat. No. 4,185,644 to Heitmann, and the rod forming and subdividing unit is described, for example, in commonly owned U.S. Pat. No. 4,280,516 to Reuland.
If the cigarettes are to be assembled with filter mouthpieces to form filter cigarettes, plain cigarettes issuing from the cigarette maker are fed into a tipping machine wherein they are united with filter mouthpieces by means of adhesive-coated uniting bands consisting of so-called tipping paper. The filter cigarettes are tested for the quality of their fillers, wrappers, mouthpieces and/or junctions between the tobacco-containing portions and filter mouthpieces, and the wrapper of each filter cigarette can be provided with perforations for admission of atmospheric air into the column of tobacco smoke. A filter tipping machine which can be used with the PROTOS cigarette maker is manufactured by the assignee of the present application under the name MAX 80. Reference may be had to commonly owned U.S. Pat. No. 4,281,670 to Heitmann. Commonly owned U.S. Pat. No. 4,177,670 to Heitmann discloses a method of monitoring the permeability of the wrappers of filter cigarettes, and the U.S. Pat. No. 4,281,670 further discloses the manner in which one or more lasers can be used to perforate the wrapping material. Commonly owned U.S. Pat. No. 4,247,754 to Baier discloses an apparatus for perforating wrapping material for cigarettes or the like by discharging sparks between opposite sides of the wrapping material.
It is further known to regulate the formation of a tobacco filler in such a way that the hardness (filling power) of successive increments of the filler matches or closely approximates a preselected value. Hardness is important to the smoker because her or his fingers can readily ascertain the resistance which the filler of a cigarette offers to depression. Such hardness can be monitored and regulated in lieu of monitoring and regulating the mass or quantity of fibrous material per unit length of the filler. The reason that certain manufacturers of cigarettes prefer to monitor and regulate the hardness is that the smoker is much more likely to be positively influenced by the satisfactory hardness than by the satisfactory mass or quantity per unit length of a filler which is subdivided into the fillers of cigarettes because the hardness of a cigarette is readily detectable but not the exact weight. Hardness of cigarettes can be ascertained with a suitable densimeter, e.g., with a so-called Borgwaldt densimeter. Satisfactory or standard hardness is denoted by a certain level of the movable part of the Borgwaldt densimeter.
Density of cigarette fillers or cigarette rod fillers can be ascertained directly or indirectly. Direct monitoring of the density with flowing air is disclosed in commonly owned U.S. Pat. No. 3,921,644 to von der Lohe and in British Pat. No. 1,422,992. German Offenlengungsschrift No. 22 41 774 discloses a different mode of monitoring the hardness of the filler, namely by ascertaining the force which the compacted tobacco stream applies to the wrapping mechanism during the application of a web of cigarette paper or the like. Indirect determination of filling power of a tobacco filler is disclosed in the aforementioned U.S. Pat. No. 4,280,516 to Reuland. Signals denoting the filling power can be converted into signals denoting the hardness of the filler. Reuland proposes to relate signals denoting the mass flow to signals which denote the height of the equalized stream. Another indirect determination of the hardness of a filler is disclosed in commonly owned U.S. Pat. No. 4,290,436 to Reuland who proposes to relate signals denoting the height of the equalized stream to signals which denote the height of the unequalized stream. Commonly owned U.S. Pat. No. 4,284,087 to Reuland discloses a different indirect determination of hardness according to which signals denoting the resistance which the equalized tobacco stream offers to penetration of air are processed with signals denoting the height of the equalized stream.
Commonly owned U.S. Pat. No. 4,249,545 to Gretz discloses an apparatus for perforating the wrappers of cigarettes in dependency on a characteristic of the wrapper or filler of a cigarette. However, this reference does not disclose or propose to make the perforating operation dependent upon the mass per unit length of a filler whose hardness is constant.