Terry Arden discusses custom non-contact engine volume gauging for Tier 2 and 3 component suppliers
For automotive component suppliers that need to verify high tolerances on medium-sized internal combustion engines (ICEs), an expert in the sector has designed a 3D non-contact inspection method to replace manual measurement approaches.
Gocator Volume Checker
This automated non-contact 3D solution, called Gocator Volume Checker, combines several technologies to achieve high-speed, accurate volume measurement of engine cylinder heads and piston bowls.
Volume gauging is an important application in engine development. Each cylinder in an engine block has to be measured for correct combustion volume. Although CAD data can be used to determine nominal volume, compliance testing requires the acquisition of a large number of measurement points, their connection by line or curve approximation, and finally computation of volume displacement.
Contact-Based Methods Of Volume Gauging
Tactile coordinate measuring machines (CMMs) can accomplish volume gauging with a high degree of accuracy. However, this method can take more than two minutes per chamber, and all chambers need to be measured. As a result of the slow speed and high cost of CMMs, the vast majority of manufacturers use liquid to measure engine volume. Acoustics and pressurised air are less commonly used contact-based methods.
All three of these traditional methods are time-consuming because there is considerable set-up time involved, and only one cylinder can be measured at a time. Additional time is required for clean up after the measurement process is completed.
The Advantage Of Optical Methods
Optical methods based on structured light (fringe projection) offer a 3D scanning method that is non-contact and area based. 3D scanning with this method is significantly faster (seconds, not minutes) and produces much higher density 3D data, representing a more accurate shape of the part.
Snapshot sensors are common devices that deliver this type of 3D scanning technology. A structured light 3D snapshot sensor projects a line pattern onto the cylinder head of an engine block. The line pattern is recorded by a camera from an optimal angle, yielding information on the cylinder’s surface topology calculated from the deformation of the projected lines.
There is a clear advantage to using structured light for quality inspection. Namely, when blue-LED stripes with smooth value gradients are projected and moved across the engine block in close steps, the analysis of these values allows for a magnitude better position resolution than the single point measurement typical of CMM probing methods.
Stripe Pattern Projection
Stripe pattern projection provides coordinate resolution down to 1/50 of the projected stripe width. This means the cylinder head can be fully inspected with the acquisition of just a few dozen images with slightly shifted stripe positions (i.e. phases), which can be accomplished in just a few seconds.
The Gocator Development Kit & Volume Checker
Gocator 3210 is the hardware platform of the Volume Checker solution. The 3210 is a metrology-grade, inline ready 3D snapshot sensor that scans at 35 μm resolution, and is ideal for detecting features on large targets such as automotive cylinders.
The Gocator Development Kit (GDK) allows developers to embed their own custom measurement algorithms into the Gocator firmware. In the case of the Volume Checker, LMI has embedded a custom volume gauging tool that can scan and measure cylinder heads in less than five seconds at an accuracy of +/- 0.04cm3.
Another advantage of Gocator Volume Checker is that manufacturers aren’t required to cover the cylinder head valves before executing volume measurements. When using traditional methods, valve coverage is a standard requirement.
The GDK’s built-in custom Volume tool “caps” all openings to produce accurate 3D volume data of the chamber, without the need for manual intervention. This capability saves additional set-up time as a result.
Smart Vision Acceleration
GoX is a PC-based application that accelerates the Gocator 3210 sensors by redirecting compressed 3D scan data to a PC – for unpacking and analysis – to achieve the fast cycle times required for inline engine block inspection.
Volume Checker can also be accelerated with GoMax, a compact plug-and-play hardware device that adds 1 TeraFlop of GPU-driven data processing power to the Gocator 3210 sensors, speeding up cycle times and improving overall inspection performance.
The Master Hub 810 network controller simplifies the support of multiple sensors (up to eight) by handling power, synchronisation, laser safety (for laser-based sensors), encoder and digital I/O. A Master 810 is used to support the Volume Checker when designers want to use four sensors to scan and measure four cylinders at once.
Gocator’s flexible platform allows LMI to customise standard sensors to meet specific application requirements. This approach is the next step in improved automated quality control, where 3D smart sensors are configured to perform highly specialised inspection tasks to replace manual measurement processes and achieve higher accuracy.
Terry Arden is CEO of LMI Technologies