CMM vendors have developed techniques to address this challenge, often by using the CMM as a dedicated gaging tool that requires human intervention each time a different part is to be measured. But as noted by Jay Elepano, a systems analyst with Mitutoyo America Corp. (Aurora, IL), "Using a CMM in this way doesn't allow you to implement a lot of the tools that make a CMM special, especially the software features."
A better way
At Mitutoyo, Elepano has come up with an approach to CMM integration that can better cash in on the machine's full powers in an automated factory environment. The starting point was a simple CMM operator interface called the Universal Inspection Interface (UII), which is part of Mitutoyo's MeasurLink line of statistical process control software for Windows.
The UII enables a human operator to go to a CMM, quickly pull up a menu of available part measuring programs, click on the correct program for the part being presented to the CMM, and click again to start the measuring process. But for flexible automation setups, Elepano has developed a way to take the human out of the process, by enabling communication through the UII between the CMM and other factory machines -- including robots, cell controllers, machining centers and other gear -- despite incompatibilities that may exist among the equipment types.
The solution was to write "wrappers." A wrapper takes information from one communication format and changes it to another format. The UII relies on the TCP/IP (Transmission Control Protocol/Internet Protocol) network protocol and other specifications. But if the CMM needs to communicate with a machine that uses a communication scheme such as a programmable logic controller (PLC) or serial RS-232 connection, a wrapper can be written to adapt the UII to enable the data transfer. The wrappers eliminate the human component in the human-machine interface by sending signals back and forth between the equipment. These signals tell the machines what part was processed, what measurement routine should be called up and if the part has passed.
"I can butt up to just about anything by writing a wrapper to my interface," Elepano says. "If I am butting up to an older robot that still uses a PLC (or I/O driver), then I can put a data acquisition card on my PC and change my TCP/IP code to a PLC handshake. This gives us legacy."
In a typical example, a robot presents a part to a CMM, which measures the part and feeds back information on its quality. If the part is good, the robot will offload it and it will continue down the production line. If the part is bad, it may signal the machining center to stop running because it is making bad parts. In another application, it can provide offsets to the machining center or the electrical discharge machine. "This process feedback has been done historically with dedicated gaging. Now, with a CMM, you have a flexible gage instead a dedicated fixture," Elepano says. "That makes your cell a flexible manufacturing cell as opposed to a dedicated manufacturing cell."
UII as a stand-alone piece of software is $2,500. Additional data acquisition cards may be needed as well as additional programming time, which could raise the cost. If a company wants to write its own wrappers, Mitutoyo can provide the customer with the code to hook up to the CMM both in Visual Basic or Visual C++. The company will send a kit with the open source code.
Mitutoyo has released the source code with the hope that third party software vendors will develop products based on it. So far none have done so, but Elepano has high hopes.
"When Microsoft made development tools so it was easy to write programs based on their Windows platform, there was a flood of programs released," he says. "The easier we can make it on a Fanuc or Makino or other machine tool distributors, the more they are going to push our product."
For more information on the Universal Inspection Interface, contact:
Mitutoyo America Corp.
965 Corporate Blvd.
Aurora, IL 60504
- The Universal Inspection Interface ties CMMs to production machinery and material handling equipment such as robots by allowing them to talk to each other through software "wrappers."
- The robot confirms the part to be measured and a signal is sent to the CMM telling it which part program should be run.
- If a CMM finds that a part is not within tolerance, a signal can be sent back to the robot to offload the part, which can then be sent to the scrap heap, or back to the production machine for reworking.