fig1 shows a system in accordance with the principles of the present invention for providing firmness control at a cigarette maker 1 . the latter maker can be of conventional type such as that manufactured by molins ltd . of the united kingdom under model number mk . 8 or mk . 9 . in typical operation , the maker 1 provides a continuous cigarette rod which is cut into lengths to provide individual cigarettes . during this operation , it has been proposed to control , amongst other parameters , the firmness of the rod so that it is maintained at a preselected or target firmness value . resulting from this control are cigarettes having substantially the same feel , this being a cigarette characteristic desired by cigarette smokers . in the present practice , firmness control is effected in a manner which affords greater economy and efficiency to maker operation . more particularly , in accordance with the present invention , a moisture sensor 2 and a firmness sensor 3 are utilized to provide output electrical signals m s and f s related to the moisture content and the firmness of the cigarette rod of the maker 1 . these signals are together processed in a signal processor 4 which provides an output control signal c for controlling the tobacco content being provided by the maker to the cigarette rod . in conventional manner , the control signal c might be employed to adjust the height of the ecreteur blade used to cut the tobacco stream at a given depth during rod formation . alternatively , the control signal c might be used to control the tobacco feed to the maker hopper to obtain the desired tobacco content control . such practices are disclosed , for example , in the aforementioned u . s . pat . no . 3 , 595 , 067 . the processing operations of the signal processor 4 involve the generating of a rod moisture content signal m c from the moisture sensor signal m s and the formation of a corrected rod firmness signal f cor from the firmness sensor signal f s . the moisture content signal m c is utilized to determine the content of the firmness sensor signal f s attributable to cigarette rod moisture changes referenced to a target or desired rod moisture value m t . the resultant rod firmness content signal f sm is combined with the firmness sensor signal f s to provide the corrected firmness signal f cor . comparison of the corrected firmness signal f cor with a preselected or target cigarette rod firmness value f t provides the control signal c . it is known that for a particular tobacco blend , maker cigarette rod firmness is a linear function of rod moisture content . rod firmness attributable to moisture can thus be expressed as follows : where k 0 is a constant determined by the tobacco blend and the rod weight per unit volume and k 1 is a negative constant determined by the tobacco blend only . firmness content attributable to moisture referenced to target moisture is therefore given as the signal processor 4 determines the control signal c based on the expressions 1 - 4 and , for example , might take the form of a general or special purpose digital computer programmed in accordance with the latter expressions and having stored therein the target values and appropriate constants . a typical microcomputer might be an intel system 80 / 204 provided with an intel system sbc 116 board . interfacing such microcomputer with the analog signals m s , f s and c might typically be a model mp 8418 - pga - ao burr - brown a / d - d / a converter . as above - noted , the signal processor 4 first processes the moisture sensor signal m s to generate the moisture content signal m c . this processing procedure depends to a large degree on the particular moisture sensor being used and is designed to provide a signal which is representative of the actual or true rod moisture content . where the characteristics of the moisture sensor are such that the sensor signal m s is itself representative of true rod moisture content , then this processing is carried out by equating m c to m s . on the other hand , where the sensor characteristics result in an m s signal varying from true rod moisture content , adjusting factors are provided to account for the influence of the sensor characteristics . in actual practice , these adjusting factors can be empirically determined for each particular moisture sensor . as will be discussed hereinbelow , in further practice in accordance with the present invention , a further sensor 5 for sensing the mass or density of the cigarette rod is employed for enabling moisture sensor signal adjustment . in still further practice under the present invention , a speed or velocity sensor 6 may be provided for cigarette rod speed determination and included for sensor signal adjustment . a first sensor which might be employed for the sensor 2 could be a resistance type moisture sensor . such a sensor might be formed on the above - mentioned conventional maker by inserting probes through apertures spaced along the length of the so - called tongue of the maker whereat the rod is being formed , the probes being of sufficient length to enter into the rod tobacco . a current or voltage could then be supplied to the probe and the resultant voltage or current through the probe circuit measured to determine the tobacco rod resistance and , therefore , the rod moisture content . in particular , such probes could serve as inputs to the internal circuitry of a model no . tm - 80 sensor manufactured by testron to provide the moisture measurement . utilizing such a resistance moisture sensor provides a moisture sensor signal m s requiring adjustment for arriving at the actual rod moisture content m c . in particular , it has been found that the sensor moisture signal m s requires adjustment related to rod firmness and rod speed . thus , for this sensor , moisture content can be expressed as follows : where a 0 - a 3 are constants which can be empirically determined for each particular tobacco blend and resistance sensor . with the resistance type sensor , the signal processor 4 utilizes the sensor signal m s , the firmness sensor signal f s and the speed sensor signal s to derive the moisture content signal m c based on the expression 5 . where the processor 4 is a digital computer , the computer is programmed in accordance with such expression to provide calculation of the moisture content m c . another technique for monitoring rod moisture content utilizes microwave components and depends upon microwave power absorbed largely by the moisture in the cigarette rod as it moves through a suitable microwave cavity . with this type of moisture sensor , the moisture sensor signal m s is a function of reflected and transmitted microwave power values in the absence and presence of the cigarette rod , these values being suitably adjusted for temperature variations , of the cavity and / or the rod . hence , m s is as follows : ## equ1 ## where r a and t a are temperature adjusted values of the reflectance and transmittance of microwave power in the absence of the cigarette rod and r p and t p are temperature adjusted values of the reflectance and transmittance in the presence of the cigarette rod . in this case , the obtained sensor signal m s requires adjustment related to the mass of the cigarette rod . hence , the moisture content is given as : again , in this situation the constants b 0 and b 1 can be empirically determined for the particular tobacco blend and microwave sensor being used . also , the processor 4 , if a digital computer , would now be programmed in accordance with the expression 6 to determine the moisture content m c . the firmness sensor 3 utilized with the present invention can be of a strain gauge type and may , for example , be of a type as shown and described in u . s . pat . no . 4 , 033 , 360 . such a firmness sensor may be used with either of the above - described moisture sensors . additionally , the mass sensor 5 might be a beta gauge type manufactured by molins ltd , and supplied with their model number mk 8 or mk 9 . the speed sensor 6 , on the other hand , might be a simple tachometer of conventional design yielding a value of voltage to represent revolutions per minute . a particular example of the present practice was carried out for a standard cigarette blend and target values m t and f t equal to 12 . 5 % and 2 . 5 , respectively , using a resistance sensor to measure m s and a strain gauge to measure f s . in this case , the constants k 1 and a 0 through a 4 were determined to have the following approximate values . ______________________________________ a . sub . 0 15 . 0 a . sub . 1 0 . 43 a . sub . 2 - 1 . 0 a . sub . 3 0 . 00050 k . sub . 1 - 0 . 838______________________________________ in all cases , it is understood that the abovedescribed arrangements are merely illustrative of the many possible specific embodiments which represent applications of the present invention . numerous and varied other arrangements can readily be devised in accordance with the principles of the present invention without departing from the spirit and scope of the invention .
a practice for controlling cigarette rod firmness in a cigarette maker wherein a detected cigarette rod firmness signal is corrected for firmness variations resulting from changes in rod moisture relative to a preselected or target moisture via a suitably processed detected moisture signal and the corrected firmness signal is compared with a preselected or target firmness to derive an error signal for tobacco content control .