Printing apparatus controls

In apparatus for printing on a sequence of sheets of material in turn at a printing station, each with a different one of a sequence of printing plates, which apparatus includes means for feeding plates one by one into and away from the printing station, and printing means for causing each plate to print upon the corresponding sheet while both are at the printing station, the improvement which comprises:

• a sensing element coacting directly with the sheets in the printing station for sensing directly the presence or absence of a sheet in the printing station and generating signals indicative of each conditions;
• a sensing element coacting directly with the sheets just downstream from the printing station for sensing directly the presence or absence of a sheet in the process of leaving the printing station, and generating signals indicative of each condition;
• a sensing element coacting directly with the plates in the printing station for sensing directly the presence or absence of a plate at the printing station and generating signals indicative of each condition;
• circuit means for receiving and analyzing the signals generated by all of said sensing elements and determining whether or not, at the time for initiating a printing operation, the following conditions exist:
• 1. a sheet is present in the printing station,
• 2. a sheet has at some time since the previous printing operation appeared at a point just downstream of the printing station,
• 3. a plate is present in the printing station,
• 4. a plate has at some time been absent from the printing station since the previous printing operation, to thereby provide indication as to whether the sheet and plate have been changed,
• said circuit means including means for generating a signal for preventing operation of the printing means to cause printing unless all of said conditions 1, 2, 3 and 4 are affirmative.

In apparatus for printing on a sequence of sheets of material in turn at a printing station, each with a different one of a sequence of printing plates, which apparatus includes means for feeding sheets one by one into and away from the printing station, and printing means for causing each plate to print upon the corresponding sheet while both are at the printing station, the improvement which comprises:

• a sensing element coacting directly with the sheets in the printing station for sensing directly the presence or absence of a sheet in the printing station and generating signals indicative of each condition;
• a sensing element coacting directly with the sheets just downstream from the printing station for sensing directly the presence or absence of a sheet in the process of leaving the printing station, and generating signals indicative of each condition;
• circuit means for receiving and analyzing the signals generated by both of said sensing elements and determining whether or not, at the time for initiating a printing operation, the following conditions exist:
• 1. a sheet is present in the printing station,
• 2. a sheet has at some time since the previous printing operation, appeared at a point just downstream of the printing station, to thereby provide indication as to whether said sheet has been changed,
• said circuit means including means for generating a signal for preventing operation of the printing means to cause printing unless both of said conditions 1 and 2 are affirmative.

In apparatus for printing on a sequence of sheets of material in turn at a printing station, each with a different one of a sequence of printing plates, which apparatus includes means for feeding sheets one by one into and away from the printing station, and printing means for causing each plate to print upon the corresponding sheet while both are at the printing station, the improvement which comprises:

• a sensing element coacting directly with the plates in the printing station for sensing directly the presence or absence of a plate in the printing station and generating signals indicative of each condition;
• circuit means for receiving and analyzing the signals generated by said sensing element and determining whether or not, at the time for initiating a printing operation, the following conditions exist:
• 1. a plate is present at the printing station,
• 2. a plate has at some time been absent from the printing station since the previous printing operation, to thereby provide indication as to whether said plate has been changed,
• said circuit means including means for generating a signal for preventing operation of the printing means to cause printing unless both of said conditions 1 and 2 are affirmative.

Apparatus for printing on each one of a plurality of sheets of material in turn at a printing station with a plurality of printing plates comprising:

• first sheet feed means for moving each of the sheets into the printing station;
• second sheet feed means for moving each of the sheets in turn away from the printing station;
• plate feed means for moving each of the printing plates in turn into and away from the printing station;
• printing means for causing each plate to print upon the corresponding sheet while both are at the printing station, said sheet feed means, plate feed means and printing means being cyclically operable in time relation to each other to effect the printing process;
• first sensor means including a sensing element coacting directly with the sheets downstream of the printing station for directly detecting the presence or absence of a sheet downstream of the printing station during a cycle period in which a printed sheet normally would be in the process of being removed from the printing station by the second sheet feed means and for generating signals indicative of the present or absent condition;
• second sensor means including a sensing element coacting directly with the sheets in said printing station for directly detecting the presence or absence of a sheet in the printing station after the operation of the first sheet feeding means and during a period in the cycle just preceding the printing operation, and for generating signals indicative of the present or absent condition;
• and control means for said printing means connected to said sensor means for preventing operation of said printing means in response to a signal by either of said sensor means representing the absence of a sheet, thereby indicating failure to change the sheet between impressions.

Apparatus for printing on each one of a plurality of sheets of material in turn at a printing station with a plurality of printing plates comprising:

• sheet feed means for moving each of the sheets into and away from the printing station;
• plate feed means for moving each of the printing plates in turn into and away from the printing station;
• printing means for causing each plate to print upon the corresponding sheet while both are at the printing station, said sheet feed means, plate feed means and printing means being cyclically operable in time relation to each other to effect the printing process;
• sensor means including a sensing element coacting directly with the printing plates in the printing station for directly detecting the presence or absence of a printing plate in the printing station at a first cycle time at which a printing plate normally would have been removed from the printing station and before the subsequent plate is fed, and the presence or absence of a succeeding printing plate in the printing station, during a second cycle time after the cycle plate feeding operation, and just prior to the printing operation, and for generating signals indicative of the present or absent condition in each case;
• and
• control means for said printing means connected to said sensor means for preventing operation of said printing means either in response to a signal by said sensor means representing the presence of a plate during the first cycle time, or the absence of a plate during the second cycle time, thereby indicating failure to change the plate between impressions.

Apparatus for printing on each one of a plurality of sheets of material in turn at a printing station with a plurality of printing plates comprising:

• first sheet feed means for moving each of the sheets into the printing station;
• second sheet feed means for moving each of the sheets in turn away from the printing station;
• plate feed means for moving each of the printing plates in turn into and away from the printing station;
• printing means for causing each plate to print upon the corresponding sheet while both are at the printing station, said sheet feed means, plate feed means and printing means being cyclically operable in time relation to each other to effect the printing process;
• first sensor means including a sensing element coacting directly with the sheets just downstream of the printing station for directly detecting the presence or absence of a sheet downstream of the printing station during a cycle period in which a printing sheet normally would be in the process of being removed from the printing station by the second sheet feed means and for generating signals indicative of the present or absent condition;
• second sensor means including a sensing element coacting directly with the sheets in said printing station for directly detecting the presence or absence of a sheet in the printing station after the operation of the first sheet feeding means and during a period in the cycle just preceding the printing operation, and for generating signals indicative of the present or absent condition;
• third sensor means including a sensing element coacting directly with the printing plates in the printing station for directly detecting the presence or absence of a printing plate in the printing station at a first cycle time at which a printing plate normally would have been removed from the printing station and before the subsequent plate is fed, and the presence or absence of succeeding printing plate in the printing station, during a second cycle time after the cyclic plate feeding operation, and just prior to the printing operation, and for generating signals indicative of the present or absent condition in each case;
• and
• control means for said printing means connected to said sensor means for preventing operation of said printing means in response to a signal by either of said first or second sensor means representing the absence of a sheet, or in response to a signal by said third sensor means representing the presence of a plate during the first cycle time, or the absence of a plate during the second cycle time, thereby indicating failure to change the sheet or plate between impressions.