Pallet Stacker

Pallet Stacker Automation Using Basic Stamp

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 (Revision D) 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 lifts up the arms and energizes the chain motor. After an adjustable amount of time, the Basic Stamp lowers the arms. The chain continues to pull the pallet back towards the lifting/stacking pneumatic cylinder. Using the Basic Stamp 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 to stop the chain motor and raise, then lower, the pneumatic lifting cylinder. The Basic Stamp 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 beeps different pattern. If a certain mechanical device is not working, one can listen to make sure that the Basic Stamp is going over the line of code that should energize that device.

Here is a 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 closeup of the basic stamp.

Accomplishments

Verified that both air valves worked
Verified that both switches worked
Sorted and labeled existing wiring
Attempted to use original relays
Found out additional parts would be needed to have arms drop before chains stop.
Made working electromechanical model from parts I had
Decided it would be more efficient to use controller
Confirmed that the model ran the pallet stacker
Researched best micro-controller value
Ordered BASIC Stamp programmable logic controller (PLC)
Studied manual and learned how to program PLC
Studied wiring diagram and built programming
Designed and built power supply
Researched motor amperage to determine needed solid-state relay (SSL) ratings
Researched SSLs from 5 companies
Ordered two 1.5 Amp SSLs & one 5 Amp SSL
Ordered foot pedal
Assembled and tested PLC
Installed PLC
Sealed control box

This chart shows how the I/O pins of the Basic Stamp were connected.

Download the pBasic listing: Pallet.bas

Parts were ordered from these companies:

Parallax, Inc	www.parallaxinc.com	1(888) 512-1024
All Electronics Co.	www.allelectronics.com	1(800) 826-5432
Paul J's Basement Co	www.JordanAutomations.com	1(360) 733-6347

The following items were purchased for the pallet stacker.

Description	Paid	Retail	Company	Additional Information
BASIC Stamp Version D	$29.00	$200.00	Parallax	Programmable Logic Controller
BASIC Stamp Software	$2.50	Included	"	Programming software & demos
Stamp Programming Cable	$0.00	$20.00	PJ Co.	Assembled from personal supplies
Stamp Programming Manual	$10.00	$35.00	PJ Co.	Downloaded from web-site. Printing costs: 5c a page X 200 pages
Shipping	$6.00	---	Parallax	Â�
Footswitch	$5.50	$20.00	All Elec.	Industrial footswitch
Solid-state Relay, 1.5 Amp x2	$8.00	$400.00	"	One for each air valve
Solid-state Relay, 5 Amp	$4.00	$200.00	"	Motor controlling relay
Solid-state Relay, 2 Amp	$2.00	$200.00	"	Backup relay
Header, 1 X 40	$0.50	$1.00	"	Programming connector
Disk Capacitor, 0.1mf 25V	$1.00	$5.00	"	Power supply component
All Electronics Shipping	$5.00	---	"	Power supply component
Transformer, 6VAC	$5.00	$8.00	PJ Co.	Power supply component
Bridge Rectifier	$2.00	$5.00	"	Adjusts 'arm' drop time
Potentiometer	$2.00	$2.00	"	Solder, wire, flux, glue
Jacks and other misc.	$1.00	$1.00	"	Â�
Total	$83.50	$1102.00!!	Â�	Â�

Paul Jordan

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