Skokie, IL —Designers of ink jet printers may soon have a better way to dispense ink, thanks to a new piezo valve that offers higher speed and lower cost.
The new valve, known as the Solid State Solenoid Valve, reportedly achieves printing speeds at least three times as fast as those of the conventional solenoid valves. It's also less than half the size and cost of conventional units, its inventor says.
The design is specifically intended for so-called "drop-on-demand" printing, which is typically employed to place alpha-numeric characters on cardboard cartons and other containers. The new technology cannot be used, however, in the bubble-type printers associated with personal computers.
Applying a voltage to the piezo element causes it to arch upward, which relieves pressure on the ball and allows ink to flow through the nozzle.
Key to the new valve is its piezoelectric element to dispense ink. In that sense, it contrasts sharply with conventional ink jet printing valves, which use tiny, ultra-high-speed solenoids to produce the microscopic ink drops. The best of those solenoids have strokes measured in thousandths of an inch, and operate at frequencies of about 300 Hz.
In contrast, the Solid State Solenoid Valve operates at about 1000 Hz. To accomplish that, it uses a piezoelectric bender made from nickel-steel bonded to a piezoceramic layer. The valve also uses a ball that rests atop a thin rubber membrane, sealing off the ink supply. When the valve is not in use, one end of the cantilevered piezo element rests atop the ball. By pushing the ball down against the surface of the membrane, the piezo prevents flow of ink out the valve's exit port.
When electrical current is applied, the tip of the bi-metal piezoelectric element arches upward, and the entire element bends like an unloaded cantilever beam. This removes pressure from the plunger, thus allowing ink to flow from the exit port. The result is a tiny drop of ink that gets ejected from the printer nozzle.
Using this technique, the Solid State Solenoid can create ink bubbles ranging from 0.25-mm to almost 1-cm diameter. The valve's inventor, Burt Siegal of Budd Engineering, says that the valve controls bubble size by controlling the length of the electrical pulse. The ink pressure can be varied by using a pressure regulator. The system typically operates at about 7 psig.
Siegal says that the piezo element can open and close the port in about 1 ms. That 1,000 Hz frequency is 3 to 5 times faster than conventional solenoid valves. "The difference is that conventional solenoids are limited by their own mass and inertia," he says, which limits conventional units to 200 to 300 Hz.
Another advantage of the piezo design is its cost. Siegal estimates that a bank of eight valves—the amount typically used in printer heads—would cost about $120. A bank of eight conventional solenoid valves, he says, would cost about $300 or more. Because the rubber membrane serves several functions, he says, it also enhances simplicity and reliability. "The beauty of this device is that one little strip of rubber does everything, " Siegal says. "It serves as the valve seat and the gasket for all eight valves."
Additional details...Contact Burt Siegal, Budd Engineering Corp.; Tel: (847) 675-2277; Fax: (847) 675-2281.