Abstract:
A printing system having a registration system for use with a variety of different types of media. The printing system is suitable for use with labels (with gaps or I-marks), continuous plastic (with I-marks), and bags (with perforations). The printing system includes a system for registering perforations ( 30 ) including a vacuum probe ( 34 ), vacuum sensor ( 36 ) and detection circuitry ( 38 ) to detect perforations. The printing system also includes a system for registering contrasting I-marks ( 10 ) appearing on a transparent media.

Description:
RELATED APPLICATIONS 
     This is a continuation-in-part Ser. No. 08/650,861 filed on May 20, 1996, abandoned and Ser. No. 08/749,593 filed Nov. 15, 1996, now pending. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a printing system, and more particularly to a printing system which has a selective registration system for various types of media. 
     BACKGROUND OF THE INVENTION 
     The need often arises to print onto a variety of different types of media, including labels (e.g., thermal transfer labels and direct thermal labels), continuous plastic, and perforated bags. Labels may be adhered to a label backing paper with a small gap between each individual label (i.e., die cut stock). Alternatively, the labels may take the form of a single continuous sheet of paper adhered to a label backing paper. A printed “I-mark” located on the back side of the label backing paper is provided to indicate where individual labels are to be cut from the single continuous sheet. The I-mark typically takes the form of a contrasting mark (e.g., an opaque printed mark). It should also be noted that the label stock may take the form of a continuous sheet of paper adhered to a label backing paper, but without any I-mark. In this case no registration is done. The continuous plastic is typically transparent or colored plastic arranged on a roll. An I-mark is provided on the continuous plastic to indicate where the plastic sheet is to be cut and separated into individual pieces. The perforated bags are typically transparent plastic bags arranged on a roll. The perforations are provided to separate individual bags from the roll. Accordingly, the perforations also indicate the beginning and end location of each bag on the roll. 
     It should be appreciated that the gaps, I-marks and perforations are important to indicate a reference position for the media. In this regard, registration of the reference position allows a printing system to determine a fixed position on the media. Thus, printing can be initiated at a predetermined position on each label, plastic sheet, or bag relative to the reference position indicated by the gap, I-mark, or perforation. 
     A typical prior art printing system includes a pair of optical sensors for detecting gaps between labels and detecting an I-mark printed on the back of the label backing paper. An IR emitter is provided to emit light toward the label backing paper. The first optical sensor is a transmissive sensor for detecting the amount of light passing through the label backing paper to determine when a gap is present. The second optical sensor is a reflective sensor for detecting the change in reflectance to determine when a printed I-mark is present. Light traveling through the label backing paper is sensed by the transmissive sensor, while light reflected by the label backing paper is sensed by the reflective sensor. It should be understood that the amount of light sensed by the transmissive sensor will increase when a gap is present or there is an absence of media, while the amount of light sensed by the reflective sensor will decrease when an I-mark is present. 
     One drawback to the foregoing prior art printing system is that in the I-mark detection operating mode the system uses the reflective sensor to detect an I-mark, while simultaneously using the transmissive sensor to detect an “out-of-paper” condition (i.e., the absence of media). Accordingly, when the transmissive sensor detects an increase in the level of light passing through the media, it detects an “out-of-paper” condition, which causes printing to halt. The “out-of-paper” condition indicates that there is no remaining media to print upon, and that print operations should be halted. Therefore, when clear continuous plastic is run through the printing system, the printer will detect an “out-of-paper” condition, since the transmissive sensor will detect the high level of light passing through the clear continuous plastic. Therefore, prior art printing systems of this type are not suitable for printing on clear continuous plastic. 
     Another drawback to the prior art printing system is that it is not capable of registering perforations. Accordingly, the prior art printing system is not suitable for printing on a media having perforations, such as plastic bags arranged on a roll and separated by perforations. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a printing system which is suitable for printing on different types of media, including labels (e.g., thermal transfer labels and direct thermal labels), continuous plastic, and perforated bags. 
     It is another object of the present invention to provide a printing system which registers gaps, I-marks and perforations. 
     It is still another object of the present invention to provide a printing system which provides a unique, efficient and inexpensive system for registering gaps, I-marks and perforations. 
     It is still another object of the present invention to provide a printing system having power rewind and unwind system for positioning a media for printing thereupon. 
     It is yet another object of the present invention to provide a printing system having a tension control system for maintaining tension on a media to be printed upon. 
     It is yet another object of the present invention to provide a printing system which allows printing on multiple types of media, registration of the multiple types of media, and which can be implemented through simple modifications of existing printing systems. 
    
    
     Still other objects and advantages and benefits of the present invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description of a preferred embodiment taken together with the accompanying drawings and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may take physical form in certain parts and arrangements of parts, a preferred embodiment and method of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
     FIG. 1 is a diagram of a system for detecting gaps and I-marks on various types of media; 
     FIG. 2 is a block diagram of a perforation detection system according to a preferred embodiment of the present invention; 
     FIG. 3 is a timing diagram of the output of a vacuum sensor of the perforation detection system shown in FIG. 2; 
     FIG. 4 is a perspective view of the printing system according to a preferred embodiment of the present invention; 
     FIG. 5 is a side view of the printing system shown in FIG. 4; 
     FIG. 6 shows a vacuum probe assembly according to a preferred embodiment of the present invention; 
     FIG. 7 shows a vacuum probe according to a preferred embodiment of the present invention; 
     FIG. 8 shows a brass tubing according to a preferred embodiment of the present invention; and 
     FIG. 9 shows a staking bushing according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is directed to a printing system in which various types of media can be printed upon, including labels (with gaps or I-marks) continuous plastic (both clear and colored, with I-marks), and plastic bags (both clear and colored, with perforations), and a printing system in which gaps, I-marks and perforations can be registered. 
     The printing system includes a gap/I-mark detection system  10  which is selectable between various modes of operation. In a first mode of operation, the gap/I-mark detection system operates to register gaps for a translucent media. In a second mode of operation, the detection system operates to register I-marks for a translucent media. The translucent media may include label stock and colored plastic. A third mode of operation is provided to register I-marks for a transparent media, such as clear plastic. 
     Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows a gap/I-mark detection system  10  for detecting gaps and I-marks on various media. Gap/I-mark detection system  10  is generally comprised of an IR emitter  12 , a transmissive sensor  14 , and a reflective sensor  16 . IR emitter  12  passes light through media  2  as it moves through detection system  10 . It should be appreciated that IR emitter  12  is suitably replaced by other types of emitters emitting visible or non-visible light. 
     In the first mode of operation, transmissive sensor  14  is used to register a gap on a translucent media, such as label stock. In this respect, transmissive sensor  14  detects the amount of light passing through media  2 . When the amount of light passing through media  2  reaches a threshold level, transmissive sensor  14  determines that a gap is present. In this regard, the amount of light passing through media  2  will increase when a gap is present. It should be noted that in this mode of operation reflective sensor  16  is inactive. 
     In the second mode of operation, reflective sensor  16  is used to register an I-mark on a translucent media, such as label stock. In this respect, reflective sensor  16  detects the change in reflectance when a printed I-mark is present. In this regard, the amount of reflectance from the light transmitted by IR emitter  12  will decrease when the printed I-mark on media  2  passes through detection system  10 . It should be appreciated that in the second mode of operation transmissive sensor  14  is active to detect an “out-of-paper” condition. Therefore, transmissive sensor  14  detects an increase in the level of light in the absence of media  2 , and generates an “out-of-paper” condition, causing printing operations to halt. 
     As noted above, prior art printing systems use the transmissive sensor to detect an “out-of-paper” condition when the reflective sensor is being used to register an I-mark. Therefore, printing on a transparent media cannot be carried out since the transmissive sensor detects an “out-of-paper” condition, due to the passing of light through the media from the IR emitter to the transmissive sensor. 
     To address the foregoing problem, the present invention provides a third mode of operation, where gap/I-mark detection system  10  operates to register I-marks on a transparent media, such as clear plastic. In this mode of operation, reflective sensor  16  is disconnected, and the inputs originally connected to reflective sensor  16  (i.e., I-mark detector) are connected to transmissive sensor  14 , replacing the original inputs to transmissive sensor  14 . Therefore, in the third mode of operation, reflective sensor  16  is inactive, and transmissive sensor  14  is active. Accordingly, when an I-mark moves past transmissive sensor  14 , a decrease in the amount of light reaching transmissive sensor  14  from IR emitter  12  will be detected. Consequently, an I-mark will be detected. It should be appreciated that since the original inputs to transmissive sensor  14  are disconnected, no “out-of-paper” condition is detected. 
     In a fourth mode of operation, the printing system operates to register perforations for bags (e.g., clear or colored plastic bags). For this operating mode, a perforation detection system  30  is provided. Perforation detection system  30  will now be described with reference to FIG.  2 . In this mode of operation, transmissive sensor  14  and reflecting sensor  16  are disconnected, and thus both are inactive. Perforation detection system  30  is generally comprised of a vacuum generator  32 , a vacuum probe  34 , a vacuum sensor  36 , detection circuitry  38  and timers  40 . Vacuum generator  32  is preferably a small AC-powered vacuum pump which provides a vacuum supply. The vacuum supply is routed to vacuum probe  34  having small slits  35 , as best seen in FIG. 6 discussed below. As perforated bags pass over the vacuum probe slits, vacuum sensor  36  will detect changes in the vacuum. In this regard, when no perforation is over vacuum probe slits  35 , the vacuum generated by vacuum generator  32  draws the bag against the vacuum probe slits to form a seal. As a result, vacuum sensor  36  registers a full vacuum. It should be noted that a tension control system may be used with the bags to provide an improved seal with the probe slits. When a perforation passes over the vacuum probe slits, the vacuum seal is broken, and consequently air rushes in, reducing the vacuum. As a result, vacuum sensor  36  registers a reduced vacuum. Vacuum sensor  36  signals the changes in the vacuum level to detection circuitry  38 . It should be appreciated that the output signal of vacuum sensor  36  characteristically has a sharp rising edge when a perforation is present, as will be discussed below. Detection circuitry  38  includes a voltage comparator, for comparing the voltage of the output signal from vacuum sensor  36  to a threshold voltage. When the output signal is greater than the threshold voltage, the output of detection circuitry  38  changes state to trigger timers  40 . Timers  40  consist of two timers. The first timer is connected to the inputs which have been disconnected from transmissive sensor  14 . Accordingly, the first timer sends a signal simulating a “gap” detection signal. The second timer is used for temporarily raising the threshold voltage for detecting a perforation. Accordingly, the second timer is used to prevent the generation of further “gap” detection signals for a predetermined period of time. In this regard, due to the extreme sensitivity of the printer to gap detection signals, the gap detection circuitry output signal can sometimes result in several “gap” detection signals for the same perforation. 
     Referring now to FIG. 3, there is shown a timing diagram  50  showing an unfiltered vacuum sensor output signal A and a detection circuitry output signal B. As can be seen, output signal A of vacuum sensor  36  has some variance as the perforated bag passes over the slits of vacuum probe  34 . However, as noted above, the output signal generated by the presence of a perforation is very sharp. Unfiltered output signal A is coupled through a capacitor to eliminate the DC component of the output signal. Output signal B of detection circuitry  38  is a much cleaner signal having a sharper, more defined transition when a perforation is present. 
     Reference is now made to FIGS. 4 and 5, where the physical arrangement of printing system  60  having the features discussed above is shown in detail. It should be appreciated that printing system  60  may take the form of a modified prior art printing system, such as a TEC B-x72. Printing system  60  includes a rotary print ribbon mechanism  70  for advancing a print ribbon  72 , and a rotary power wind/unwind mechanism  90  for advancing a media  82 . The wind/unwind mechanism  90  enables the media arranged on a roll to be rewound to its original orientation after printing is completed. This is particularly useful in the case of plastic bags, where the printed bags must be arranged to be acceptable to a bagging machine. Printing system  60  also includes vacuum probe  34  having vacuum pickup slots  35 . The position of vacuum probe  34  is adjusted by a lateral adjustment screw  44 . Rotary power unwind/rewind mechanism  70  carries media  82  over vacuum probe  34 . Vacuum probe  34  is connected to vacuum generator  32  and vacuum sensor  36  via a vacuum line  42 . It should be appreciated that vacuum line  42  is connected to vacuum probe  34  at a position where media  82  passes over vacuum probe  34 . Vacuum line  42  includes a brass tubing  104  and plastic tubing  105 . Printing system  60  also includes a print head  62  (FIG. 5) and a paper gap sensor  64  including transmissive sensor  14  and reflective sensor  16 . A housing  90  houses vacuum generator  32 , vacuum sensor  36 , detection circuitry  38 , and a multi-position switch  92  for selecting the various operating modes discussed above. 
     Referring now to FIG. 6, there is shown a vacuum probe assembly  100 . Vacuum probe assembly  100  is generally comprised of vacuum probe  34  and paper gap sensor  64 . Brass tubing  104  provides a connection between vacuum probe  34  and plastic tubing  105 . A staking bushing  106  and a bowed E-ring  102  connect vacuum probe  34  to paper gap sensor  64 . 
     A detailed view of vacuum probe  34 , including dimensions and tolerances, is shown in FIG. 7. A detailed view of brass tubing  104 , including dimensions and tolerances, is shown in FIG.  8 . FIG. 9 provides a detailed view of staking bushing  106 , including dimensions and tolerances. 
     The present invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.