ITW Diagraph IJ3000, Operation Manual, Page: 63 / 94

Integrated Valve
Appendix B: Theory of Operation
5760-107 Operations Manual Rev C Page 55 of 86
Appendix B: Theory of Operation
Functional Description
The IJ3000 ink jet system prints text, autocodes (such as product counts or time and date
stamps) and/or graphics onto products as they travel by conveyor past stationary print
heads. Print can be on any one of, or a combination of, the product's sides, top, or bottom.
The conveyor speed is monitored using a variable speed encoder or a built-in fixed speed
encoder. Products are detected using a photosensor. The information to be printed is
defined as a message and is programmed into the controller via a user interface.
Print Head Daisy Chain(s)
Print heads attach to the IJ3000 in a daisy chain configuration. The first print head plugs
into a Print Head Interface Board (P1), the second print head plugs into the first, the third
plugs into the second, etc. A daisy chain can be up to 72 dots long (eight 9-dot heads, four
18-dot heads, or a combination of 9- and 18-dot heads totaling no more than 72 dots), and
an IJ3000 can have one or two daisy chains (one for each Print Head Interface Board).
Electrically, a print head daisy chain is a shift register. A shift register moves bits of informa-
tion along a line one bit at a time in step with a clocking signal. It works like this: A bit is
placed at the entrance to the line of bits and waits for the clock (step) signal. When the
clock signal is given the bit steps into the first spot on the line. The bit that occupied the first
spot in line steps to the second, the second steps to the third, the third to the fourth, and so
on until the last bit in line steps off the end of the line and is lost. Repeat the process
enough times and all of the information in the shift register is replaced. Repeat the process
72 times and you've output a column of print data. A latch (print) signal sent after the 72
dots have been shifted prints the column.
The IJ3000 always sends 72 dots of print data per column regardless of the number of print
heads on a daisy chain. On a daisy chain with less than 72 dots the first dots shifted out are
lost, not printed. For example, a daisy chain with two 18-dot heads prints the last 36 dots
sent; the first 36 dots are lost.
All daisy chain signals - DATA, CLOCK and LATCH - are generated and controlled by cir-
cuitry in the FPGA (Field Programmable Gate Array, used as a print head driver chip) on
the Print Head Interface Board.
Please note that power is applied to the print heads even when the IJ3000 is "turned off."
The only way to remove power from the print heads is to pull the plug.
Photosensor
The photosensor detects when a product is about to pass by the print heads and signals
the IJ3000 controller to start a print cycle. The photosensor signal is active low, and it must
remain low for at least one encoder pulse. Once a print cycle starts it continues to comple-
tion regardless of what the photosensor signal does.
The IJ3000 is compatible with through-beam, retro-reflective, and diffused photosensors
that work at 15VDC and have a current sinking (or open collector) output. The photosensor
plugs into the Print Head Interface Board (P2).