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 Industrial Pallet Stacker
Project submitted to Parallax by Paul Jordan
Installing a BASIC Stamp® controller on our pallet machine increased our builders' speed by 25%! The Bronco pallet builder has a bed on which an operator builds a pallet. The machine removes the finished pallet from the bed and places it at the bottom of a stack.
The Bronco Pallet Builder originally used relays and timers to control two air cylinders and a motor. Every cycle, a pneumatic cylinder would lift two arms up, which lifted the pallet off the bed. Each arm had a chain belt on it. When the pallet was lifted, the chains pulled the pallet towards the back of the machine, under a stack of pallets. When the pallet reached the back of the machine, it triggered a switch that stopped the chains. A large pneumatic cylinder lifted the pallet up into the stack, and two latches held the pallet in place.
Unfortunately, during a relocation, the control box was destroyed. Since replacing it would cost over a thousand dollars, the unit was operated manually for quite a while. Two hand-operated air valves controlled the air cylinders, and a toggle switch operated the chain motor.
 We used a BASIC Stamp Rev. D module to re-automate the Bronco. We installed a foot-pedal at the base of the machine. When the builder presses the pedal, the BASIC Stamp microcontroller lifts up the arms and energizes the chain motor. After an adjustable amount of time, the BASIC Stamp microcontroller lowers the arms. The chain continues to pull the pallet back towards the lifting/stacking pneumatic cylinder. Using the BASIC Stamp microcontroller allows the arms to be lowered sooner in the cycle, allowing the operator to start working on the next pallet earlier. This allows for 25% greater productivity over the original design. When the pallet has reached the back of the machine, it presses a paddle switch. This signals the BASIC Stamp module to stop the chain motor and raise, then lower, the pneumatic lifting cylinder. The BASIC Stamp microcontroller then waits for the operator to signal that next pallet has been completed.
Here is some technical information. Three I/O pins are configured as outputs to control the air valves and chain motor. We used a 2-amp solid-state relay to control each air valve, and a 25-amp solid-state relay to control the chain motor. The foot pedal and the paddle switch in the back of the machine are both connected to input ports. A pot is used to set the amount of time the arms stay up. Lastly, a miniature speaker is used for diagnostic purposes. At each step along the way, the BASIC Stamp module beeps different pattern. If a certain mechanical device is not working, one can listen to make sure that the BASIC Stamp microcontroller is going over the line of code that should energize that device.
 Above is the view inside the control box. You can see the power supply underneath, the filtering capacitor on the right, and the audio tranducer variable resistor on the left.
Here is a close-up of the BASIC Stamp module.
Here is the PBASIC listing that runs the pallet stacker:
Start: Low 5: Low 6: Low 7
b3=Pins & 8:If b3 = 8 Then Start:
Rem Raise Arms & Start Chain
High 5:High 6:Sound 0,(100,5):Sound 0,(110,10):Sound 0,(100,5)
Pot 1,33,b1:b1=b1/20+2
For b2=0 to b1:Pause 500
b4=pins & 8: if b4 = 0 then ReStart:
Next
Rem Lower Arms
Low 5:Sound 0,(50,5)
Rem Stop Chain & Raise Lift
SC:b3=Pins & 16:
b4=pins & 8
if b4 = 0 then ReStart:
if b3 = 16 then SC:
Low 6:
Pause 500:Pause 500: Pause 500
High 7: Sound 0,(50,10)
Rem Lower Lift
For b2=0 to 20:Pause 500: Next:Low 7
Sound 0,(120,5)
Goto Start:
ReStart:
b4=pins & 8:if b4 = 0 then ReStart:
Goto Start:
Paul Jordan
Jordan Automations
06/12/01 |
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