CNC Software Is the Sensor
Recent developments in CNC technology enable the use of add-on software for monitoring cutting conditions in the machine tool.
Over recent years, the evolution of such concepts as condition monitoring and adaptive control have been substantial. Condition monitoring, as the name implies, watched the relationship between theoretical and actual speeds and feeds, making preprogrammed or set adjustments as needed. Adaptive control was the next iteration, as the CNC could detect subtle differences in tool and workpiece conditions and adjust cutting “on the fly” as the cycle proceeded. The advance of highly complex, non-linear shapes, especially in the aerospace and medical markets, led to the transformation orientation concept. This took computation of the cutting path to a whole new level, basing it on the tooltip relationship to the workpiece combined with a look-ahead function. Additional sensing hardware and probes were required, and are still today.
A recent, further development is available that builds on these prior advances. This concept uses add-on software in the CNC unit to monitor cutting conditions and make adjustments that compensate for or correct unwanted results. The ruling principle here is to rely purely on the software to achieve these improvements. Rather than requiring additional hardware sensors, this software reads and analyzes digital signals primarily generated by the machine spindle.
This spindle condition monitoring software, aptly named AVCM (Adaptive Vibration Control Monitoring), was created by Omative Systems, a solution partner of Siemens. Once installed on the CNC, the software monitors all digital signals from the spindle and literally “learns” the cutting condition. It then adapts the motor, drive, feed and spindle speed accordingly to compensate for a variety of conditions, including workpiece material variances, distance to workpiece, cutting tool wear and more. While additional sensors are still required to monitor vibration and tension, the software detects most other conditions in process as the first parts are cut.
By its nature, this software is geared more for the high-volume producer or production department, but also intended for the mid-sized job shop or contract manufacturer handling jobs with a few hundred pieces. Because the system is based on software, it can be provided as an economical option for a single machine as well as for a multi-machine work cell or a production line with dozens of identical machines. In this latter application, each machine learns on its own and makes adjustments in process, with all data available to the upstream control operation.
Real-time conditions are continuously monitored by measuring vibration acceleration, velocity and displacement. Under high-risk vibration conditions, the system stops the machine to prevent damage to the spindle and other machine parts. Automatic readings and comparisons to the machine’s baseline vibration signature are routinely made. Significant deviations from the machine’s baseline vibration signature trigger maintenance alerts.
When installed on a CNC unit connected to a shop network, the software can enable statistics to be extracted from the machine and shared worldwide for a multi-national manufacturer or a machine tool builder looking to do comparative analysis on its installed base. In addition, the emergence of the cloud as a viable business platform today enables the CNC builder to interact with the machine builder and end user communities in ways not imagined just a decade ago. This spindle monitoring software, for example, can be monitored by the CNC provider to track real-time spindle conditions in tandem with the machine builder for design improvement possibilities, as well as by the end user for OEE data gathering.
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