The Challenge:

Developing a flexible, rugged and cost effective test system for accurate clearance measurement between tappet top to the cam lobe in IC, engine which can replace existing PLC based test system.

The Solution:

Developing a flexible, rugged cost effective test system using NI PCI-6220, NI-PCI-6527 with Lab VIEW.

Introduction:

It's often quicker and less expensive to use a shim, a thin piece of metal or composite, to level a machine tool or make components fit together than grinding and machining to make the same mechanical adjustments. Shims act like those 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, since the clearance distance directly affects the performance of the engine. It is not cost effective to get the required clearance by machining the mechanical parts rather these clearances are compensated by inserting appropriate shims.

Yet now it is an industrial practice to use feeler gauges to measure the clearance manually. This procedure has been automated with the use of NI DAQ cards along with LabVIEW, ten LVDT probes for the clearance measurement and with four pneumatic systems for the mechanical alignment of the cam shaft and cam cylinder with tappet top.

System Configuration:

The system consists of two fixture stations. One to measure the cam shaft lobe profile and other to measure tappet top positions both these measurements are with respect to a Master. The Master has the desired dimension of cam shaft lobe and cylinder tappet top.

System uses PCI-6220 DAQ card for LVDT probe measurement, and system uses PCI-6527 isolated DIO for monitoring the machine status as well to control the mechanical sequence required to bring the LVDT probe over cam shaft and cylinder tappet top.

System Implementations:

The entire system has been implemented within twenty three man days. 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. Implemented NI based Test System takes less than three seconds for the entire measurement and selection of appropriate shims which in turn increases the assembly line productivity by twenty times. The system allowed us to guarantee the measurement error of within ±10microns. Figure1 shows the schematic view of probe locations on the cam shaft and over the tappet top

The software of the system is basically divided in to two modules, manual mode and auto mode of operation

Manual Mode:

In manual mode system carries out all the mechanical actions guided by the user. Every action has its own interlock with the past actions as well as with some proximity and read switch status. Front panel of manual operation is depicted in Figure2.

Auto Mode:

In auto mode all the operations are carried out automatically after the “Cycle start” user acknowledgment. Shim sizes are calculated automatically after the LVDT probe measurement and its processing. Figure3 shows front panel for auto mode of operation.

Auto mode has the provision to stop the cycle at any time using emergency stop button, reset the current cycle to restart cycle again. In auto mode both the fixtures are operated in parallel. System guides user through the message display in the panels. System is implemented with self diagnostic features so that failure of any reads switches or proximity switches are indicated to the user appropriately. Implemented system generates the report for employee productivity of particular shift along with the selected shim values at what time

We have replaced existing PLC based shim selection machine with NI based Test System. In this application PLC fails to provide signal processing capability required by the application along with the user interface requirements.

Conclusion:

The system developed is highly flexible, rugged and cost effective. Automated system has increased the assembly line production by twenty times also ensures the measurement accuracy of ±10microns.