Test Bench (Apr 2005):
A test bench has been constructed to aid in my research of the PLC, pneumatic valves, actuators, grippers, and proximity switches. A picture of the test bench is shown below. It consists of an Allen Bradley SLC 5/02 PLC, terminal blocks, proximity switches, and pneumatic valving. Air-powered actuators can be connected to the bench and tested for functionality and performance. Most of this equipment will be mounted into a PLC enclosure and mounted to the conveyor base.
Pneumatic Valves (Mar 2005):
The pneumatic valves are manufactured by Numatics, Inc. Every individual valve assembly consists of a base, a valve, and a solenoid. Optionally, a flow control can be inserted between the base and the valve to control the flow rate of the air exiting or entering the valve. Each valve assembly is completely modular, and they can be bolted successively together to form a valve bank of any size. Each end of the valve bank contains an endplate. The top endplate has an inlet port for air supply. The bottom endplate has two outlets for exhaust in port A or port B.
Each valve in the valve assembly are four port, two position, spring return devices with default position to port A. This means that if the solenoid which controls the valve is not on, air will flow out of port A, and port B will be vented to exhaust. Conversely, if the solenoid is activated, supply air will flow out of port B, and port A will be vented to exhaust.
Nominal supply pressure for the system is 40psi, although it will operate between 10 and 100 psi. The solenoid requires 24VDC operation @100mA.
PLC Research (Feb 2005)
HP donated an Allen Bradely SLC 5/04 programmable logic controller. I researched both hardware and software aspects of this device so that I could make it operational.
The software required is made by Rockwell Automation, the parent company of Allen Bradley. The software is fairly dated, and it has only recently been available to operate on Windows 2000/XP machines. The programming software is RS Logix 500 and utilizes ladder logic diagrams as the primary programming interface. I could purchase two versions: (1) the starter version, and (2) the full version. The starter version is the same as the full version with the exception of two limitations: (1) you cannot program the PLC while in RUN mode, and (2) the PLC is limited to the type of networks it can be connected on. Since I have no need to program the PLC in RUN mode and I am running a 2 node network (my computer and the PLC), the starter version was purchased. Also, I received a significant educational discount from Rockwell. The starter version is normally in excess of $1000. I purchased it for $80.
The SLC 5/02 does not have a standard RS232 interface for direct programming. Instead, it uses RS485 network connection and the DH-485 protocol. The hardware interface is an RJ45 female connection. Because of this, I had to purchase a USB-to-RJ45 interface that converts RS485 to USB 2.0. The device is proprietary to Allen Bradley and was purchased for $250.
The unit was successfully programmed 2-4-05. The program loaded pulses an electro-pneumatic valve at 0.5 Hz only when a proximity switch is activated. The program is shown below:
SMED Research (Jan 2005):
Over the last month, I have focused on researching SMED (Single-Minute Exchange of Die). SMED is a lean technique used to minimize downtime during a tool changeover.
Preliminary research on SMED is complete. Click here to view a summary of my findings.