Customer Solutions

Automated Shim Selection Machine

Author(s):

Vijay Jayabalan, Captronic Systems Pvt. Ltd.

Industry:

Automotive

Product:

Data Acquisition, LabVIEW, PXI/CompactPCI

The Challenge:

Developing a test system for accurate IC engine clearance measurement from tappet top to cam lobe that can replace our existing PLC-based test system.

The Solution:

Developing a flexible, rugged, and cost-effective test system using the National Instruments PCI-6220 and PCI-6527 data acquisition devices with National Instruments LabVIEW.

Overall layout of the SHIM selection machine.

Using a shim – a thin piece of metal or composite – to level a machine tool or to make components fit together is often quicker and less expensive than grinding and machining to make the same mechanical adjustments. Shims act like folded pieces of paper people place under table legs to prevent the table from wobbling.

Properly adjusted valve clearances are necessary in IC engines so that the valves will open and close as they should, because clearance distance directly affects engine performance. Because it is not cost-effective to achieve the required clearance by machining the mechanical parts, these clearances are adjusted by inserting appropriately sized shims. It is now an industrial practice to use feeler gauges to measure clearance manually.

At Captronic Systems, we have automated this procedure using National Instruments data acquisition (DAQ) devices along with NI LabVIEW, 10 LVDT probes for clearance measurement, and four pneumatic systems for mechanical alignment of the cam shaft and cam cylinder with the tappet top.

System Configuration

The test system, which we created for four-cylinder engines, consists of two fixture stations, one to measure the cam shaft lobe profile and the other to measure tappet top positions – both with respect to a master, which has the desired cam shaft lobe and cylinder tappet top dimensions. The system contains 10 LVDT probes, four for tappet top measurements, another four for cam profile measurements, and two for cam base measurements. Four pneumatic systems bring the LVDT probes onto the components whose dimensions are to be measured, and light indicators designate machine statuses like “no air” and “error” and indicate initial conditions. Twenty-four digital input feedback signals confirm each action and read the machine status

The system uses the NI PCI-6220 for LVDT probe measurement and the NI PCI-6527 isolated DIO device to monitor machine status and to control the mechanical sequence required to bring the LVDT probe over the cam shaft and cylinder tappet top.

System Implementation

We implemented the entire system within 23 man-days. The power of LabVIEW helped us complete the system in such a short time span. An experienced employee takes approximately one minute to measure and select the appropriate shims manually. Error in manual measurements depends on the employee and his fatigue level. With our new test system, the entire measurement and shim selection process takes less than three seconds.

The system software is divided into manual and auto mode of operation. In manual mode, the system carries out all the mechanical actions guided by the user. Every action has its own interlock with past actions as well as with some proximity and read switch status. In manual mode, all the LVDT probe measurements are referenced against the master, and LVDT probes are adjusted to read within some predefined value in one direction to avoid polarity mismatch.

In auto mode, all operations are carried out automatically after the “cycle start” user acknowledgment. Shim sizes are calculated automatically after LVDT probe measurement and processing. The auto mode includes a provision to stop the cycle at any time using an emergency stop button and reset the current cycle to restart. In auto mode, both the fixtures are operated in parallel. The system guides the user through the message display in the panels, and self-diagnostic features indicate failure of any read or proximity switches to the user. The system generates reports for employee productivity monitoring as well as selected shim values at designated times.

The existing PLC-based shim-selection machine did not provide the signal processing capabilities and user interface requirements required by the application. Our new test system based on NI data acquisition hardware and LabVIEW software is highly flexible, rugged, and cost-effective, increasing assembly line productivity by 20X and guaranteeing measurement accuracy within ±10 microns.

For more information, contact:

Vijay Jayabalan

Captronic Systems Pvt., Ltd.

Alif Arcade, # 19

Bangalore, Karnataka, India

(91) 80 25535046

E-mail: vijay@captronicsystems.com