Printing marks on substrate edge

1 . A system, comprising:

a printing assembly, which is configured to print: (i) multiple images on multiple respective substrates, and (ii) multiple marks on one or more edges of the multiple respective substrates; and

a stacking assembly, which is configured to stack the multiple respective substrates on top of one another to form a stack having a top surface parallel to one or more of the substrates, and sides made from the stacked edges of the substrates,

wherein, one or more of the marks are visible on a side-view of at least a given side of the sides,

and wherein at least a position of the one or more marks in the side view of the given side, is indicative of a problem that occurred while printing one or more of the multiple images.

2 . The system according to claim 1 , wherein the images comprise first and second images, the marks comprise first and second marks, and the substrates comprise first and second substrates, respectively, wherein: (i) on the first substrate, the first image is printed at an intended position and the first mark is printed at a first edge position on a given edge of the edges, and (ii) on the second substrate, the second image is printed at an actual position and the second mark is printed on the given edge at a second edge position.

3 . The system according to claim 2 , wherein the problem comprises an offset between the intended position and the actual position, and wherein, in the side-view image, a difference between the first and second edge positions is indicative of the offset between the actual position and the intended position.

4 . The system according to claim 2 , wherein the first image comprises a first color image of a first color and a second color image of a second color, different from the first color, wherein the first mark comprises: (i) a first color mark associated with the first color image and located at a first color position, and (ii) a second color mark associated with the second color image and located at a second color position different from the first color position, wherein the problem comprises a registration error between the first and second color images, and wherein, in the side-view image, a distance between the first and second color positions is indicative of the registration error between the first and second color images.

5 . The system according to claim 2 , wherein the problem comprises a movement of the second substrate relative to the second image, and wherein a difference between the first and second edge positions in the side-view image, is indicative of the movement.

6 . The system according to claim 5 , wherein the movement comprises a rotation of the second substrate about an axis orthogonal to the top surface.

7 . The system according to claim 2 , wherein the first image is printed on the first substrate using a first printing job, and the second image is intended to be printed on the second substrate using a second printing job, different from the first printing job, wherein the problem comprises an operational error of using the first printing job for printing the second image on the second substrate, and wherein a difference between the first and second edge positions is indicative of the operational error.

8 . The system according to claim 1 , and comprising a processor, which is configured to receive a side-view image of the side view, and to identify the problem based on at least the position of the one or more marks in the side-view image.

9 . The system according to claim 8 , wherein, before printing the multiple marks, the processor is configured to define one or more properties of the multiple marks intended to be printed on the one or more edges.

10 . The system according to claim 9 , wherein the one or more properties comprise at least one of: (i) the position of the one or more marks in the side view, (ii) a size of the one or more marks in the side view, and (iii) a color of the one or more marks in the side view.

11 - 15 . (canceled)

16 . A method, comprising:

printing: (i) multiple images on multiple respective substrates, and (ii) multiple marks on one or more edges of the multiple respective substrates; and

stacking the multiple respective substrates on top of one another to form a stack having a top surface parallel to one or more of the substrates, and sides made from the stacked edges of the substrates, wherein, one or more of the marks are visible on a side-view of at least a given side of the sides; and

identifying a problem that occurred while printing one or more of the multiple images, based on at least a position of the one or more marks in the side view of the given side, which is indicative of the problem.

17 . The method according to claim 16 , wherein the images comprise first and second images, the marks comprise first and second marks, and the substrates comprise first and second substrates, respectively, wherein: (i) on the first substrate, the first image is printed at an intended position and the first mark is printed at a first edge position on a given edge of the edges, and (ii) on the second substrate, the second image is printed at an actual position and the second mark is printed on the given edge at a second edge position.

18 . The method according to claim 17 , wherein identifying the problem comprises identifying an offset between the intended position and the actual position, and wherein, in the side-view image, a difference between the first and second edge positions is indicative of the offset between the actual position and the intended position.

19 . The method according to claim 17 , wherein printing the first image comprises printing a first color image of a first color and a second color image of a second color, different from the first color, wherein printing the first mark comprises printing: (i) a first color mark associated with the first color image and located at a first color position, and (ii) a second color mark associated with the second color image and located at a second color position different from the first color position, wherein identifying the problem comprises identifying a registration error between the first and second color images, and wherein, in the side-view image, a distance between the first and second color positions is indicative of the registration error between the first and second color images.

20 . The method according to claim 17 , wherein identifying the problem comprises identifying a movement of the second substrate relative to the second image, and

wherein a difference between the first and second edge positions in the side-view image, is indicative of the movement.

21 . The method according to claim 20 , wherein the movement comprises a rotation of the second substrate about an axis orthogonal to the top surface.

22 . The method according to claim 17 , wherein the first image is printed on the first substrate using a first printing job, and the second image is intended to be printed on the second substrate using a second printing job, different from the first printing job, wherein identifying the problem comprises identifying an operational error of using the first printing job for printing the second image on the second substrate, and wherein a difference between the first and second edge positions is indicative of the operational error.

23 . The method according to claim 16 , and comprising receiving a side-view image of the side view, and identifying the problem based on at least the position of the one or more marks in the side-view image.

24 . The method according to claim 23 , and comprising, before printing the multiple marks, defining one or more properties of the multiple marks intended to be printed on the one or more edges.

25 . The method according to claim 24 , wherein the one or more properties comprise at least one of: (i) the position of the one or more marks in the side view, (ii) a size of the one or more marks in the side view, and (iii) a color of the one or more marks in the side view.

26 - 30 . (canceled)