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In my previous article, I introduced a mechanism known to engineers as a Scotch Yoke. It converts linear motion of a pneumatic actuator into rotary motion. With regard to the jelly filling depositor on a pastry production line, the Scotch Yoke converts the pneumatic actuator’s linear motion into the rotary motion needed to operate the depositor’s diverter valve. Now, let’s follow the Scotch Yoke’s motion in this application. When the pneumatic actuator’s piston is all the way to the left, the Scotch Yoke’s slider is all the way to the left on the guide rod. The slider pin is at the top of the slot in the yoke mechanism. The diverter valve is positioned to create a path for the jelly so it can be emptied from the pump through the nozzle. The Depositor’s Scotch Yoke Slider Is Full Left
As compressed air is introduced to the left side of the actuator’s piston, the piston moves to the right, and the slider also moves to the right. As this happens, the slider pin begins to move in the yoke mechanism’s slot, and the diverter valve shaft begins to rotate clockwise.
The Depositor’s Scotch Yoke Clockwise Rotation
After the piston moves all the way to the right, and the diverter valve shaft stops its clockwise rotation. The diverter valve is positioned to create a path between the pump and hopper so the pump can suck in jelly from the hopper. When the pump is full of jelly, compressed air is introduced to the right side of the piston. The Depositor’s Scotch Yoke Slider Is Full Right
As compressed air is introduced to the right side of the actuator’s piston, the piston moves to the left, and the Scotch Yoke’s slider also moves to the left. As this happens, the slider pin begins to move in the yoke mechanism’s slot, and the diverter valve shaft begins to rotate counterclockwise. The Depositor’s Scotch Yoke Counterclockwise Rotation
After the piston moves all the way to the left, the diverter shaft stops its counterclockwise rotation. The diverter valve is once again positioned to create a path so the jelly can flow from the pump through the nozzle. After all the jelly is emptied from the pump, compressed air is introduced to the left side of the piston to repeat the previously described motion. But what selectively admits compressed air to either the right or left of the pneumatic actuator’s piston? Next time, we’ll find out when we discuss a device called a solenoid valve. Copyright 2018 – Philip J. O’Keefe, PE Engineering Expert Witness Blog ____________________________________ |
