High Accuracy Production Testing of Clutch Drive Plates
Magal Engineering required an end of line test rig to provide a traceable quality standard of clutch drive plates in order to supply Original Equipment (OE) parts to the automotive industry.
Of importance were high accuracy, repeatability, high throughput and reliability. All were addressed with the use of the new NI Compact RIO Expansion chassis and associated modules.
About Magal Engineering Limited
Magal Engineering are Global Original Equipment suppliers to the automotive industry. The division based in Leamington Spa is AP Driveline Technologies Limited who design, develop & manufacture automotive clutches for cars, commercial, off-highway and high performance vehicles for both Original Equipment vehicle manufacturers and the aftermarket.
About Computer Controlled Solutions Ltd
Formed in 1994, Computer Controlled Solutions has produced many complex test, control and acquisition systems for industry. An Alliance member of National Instruments since 1994 with two certified LabView developers, predominantly providing advanced LabView solutions based around National Instruments hardware.
The Drive Plate (figure 2) component of typical clutch is required for transmitting torque from the engine to the driveshaft. It essentially consists of a friction plate bound by springs of varying stiffness to a central spline. The springs are required to absorb torsional vibration, thus providing a solution for driveline Noise, Vibration and Hardness (NVH) problems.
To ensure this component works as specified each one must be tested. This is carried out by rotating the central spline relative to the fixed friction plate and analysing the spring rate and hysteresis characteristics to very fine tolerances. A typical hysteresis plot with varying spring rates can be seen in the diagram (figure 3).
The original ‘Hysteresis’ machine produced approximately 20 years ago was a £250,000 large hydraulic system without the accuracy or throughput to meet specifications. The solution was for Computer Controlled Solutions to use the latest electronics and brushless motor technology to provide a system at a fraction of this price whilst at the same time improving accuracy and increasing throughput.
Computer Controlled Solutions were selected for the software and electronics control system based on their experience in this field and the number of successful test machines previously provided and maintained for Magal Engineering.
The system was based around a High Torque Jig (800Nm) and Low Torque Jig (50Nm) placed each side of a floor standing cabinet. Each jig uses a Pneumatic actuator to clamp the drive plate and a servo motor to provide a controlled angular deflection. A torque cell and encoder are then used to acquire the hysteresis data (see figure 4).
The central cabinet contains the following control and acquisition electronics:
- Intel Dual Core Pentium 3.2 GHz
- National Instruments 7811R FPGA Card
- National Instruments Compact RIO Chassis containing
- National Instruments Quad strain gauge module
- National Instruments 32 ch Digital Outputs (Sourcing)
- National Instruments 32 ch Digital Inputs (Sinking)
- Baldor Drives
The Jigs contained the following hardware:
- Baldor Brushless Servo Motors
- Alpha 220:1 Gearboxes
- Pneumatic Actuators to clamp the parts
- Applied Measurements Torque Cells
The choice of using Compact RIO based hardware was crucial to our supply of a highly accurate machine within budget. This allowed us 24 bit resolution in the acquisition of the Torque cell readings plus noise free digital acquisition and control of angle to a resolution of 0.0004 degrees.
The software was written completely within LabView 8.5 and FPGA toolkit.
As a production piece of equipment the following features were designed in:
- Minimal operator use of computer: From powering up the system the operator simply loads the part and presses the start button.
- Simple to calibrate: With the use of encoders angle re-calibration was not required. Torque calibration was built into the software and hardware by being able to check the torque readings against 3rd party load cells and displays. These units can then be sent off for annual laboratory calibration.
- Simple to Build up Tests: The supervisor is able to create or edit a test providing a library of tests for all drive plate variations.
- Well structured and searchable acquired data (TDMS Format): All of the resultant data was saved in the latest Diadem streaming format. This allows for upto 800 tests per file per day with high speed search capabilities using the XML based parameter headers.
- Parameter History Plot: The run screen was designed to include historic traces of any measured parameter. This allows the operator/supervisor to spot potential trends in the change of any result for predictive fault detection.
- Acquisition using the FPGA hardware: This allowed the acquisition of data against angle rather than time, providing a noise free, ultra-high resolution of data capture with no wasted data.
Using the Latest Version of LabView and associated hardware
Certain features of the LabView environment were key in the smooth development cycle of this machine:
- Project Environment: Since LabView 8 release the project environment has meant that you can contain all PC code, subroutines, and Input/Output information in one place. However, it will also contain all FPGA related code, all project documentation, datasheets and specifications under one roof making future servicing and maintenance easier.
- Compact RIO Digital modules: The digital input and output modules saved a complete level of intermediate wiring. Normally the computer signals are converted to/from 24v, for operating various solenoids and reading inputs, via an intermediate rail of clip on solid state relays. Using Compact RIO 24v rated modules saved all of this wiring.
- Compact RIO Strain Gauge module: This module allowed direct connection from the torque cells into the acquisition hardware thus reducing wiring and minimising noise. In software it allowed simple calibration of the transducer with self checking offset corrections down to a resolution of 100 femto Volts.
- FPGA for True Asynchronous Testing: The FPGA architecture allowed CCS to acquire data from each rig totally independently. This is normally a problem to achieve in PC based architecture and would usually result in the extra expense of a second PC or a slower synchronous throughput of parts.
- FPGA for Firmware high speed trip monitoring: The FPGA monitors torque levels at a very high rate and directly cuts power if a level above 95% is reached. This saves on external analogue hardware and has absolute deterministic response not achievable on a PC.
Since the rapid build and completion of this machine, it has had to ‘hit the ground’ running. Every part at the end of build production is tested on a 16 hour per day period and it has run perfectly.
The extreme accuracy of results has even identified key features not picked up in original design. It has also been used to feed back data used in the design stages of next generation drive plates and indicate areas to look into with the materials manufacturers.
Paul Riley is the MD and software engineer of Computer Controlled Solutions Limited who have been alliance members with National Instruments since 1994. He has an extensive physics/electronics/computing background applied to test and production machine control and data acquisition.