Smart inductives can boost flexibility of CNC machining centres

As an example of how a smart factory can use Contrinex’s smart inductive and photoelectric sensors, we look at a smart inductive sensor embedded within the spindle of a CNC machining centre at the start of a manufacturing cell.

Within a CNC machining centre, an inductive sensor checks the position of the spindle’s drawbar to ensure tool engagement. If not correct, the sensor reports via IO-Link to a PLC, which initiates an intervention.

A smart sensor comprises an onboard microcontroller, which in this application is used to log the cumulative utilisation data for the CNC’s spindle. This is reported at pre-set intervals to a process engineer via a wireless hub, and provides information for machine optimisation.

The flexibility and capability of modern CNC machining centres make them ideal for use in smart factories because of their ability to cope with a wide range of tasks. They are able to handle various materials, batch sizes, work-pieces, tools and cutting speeds that might have previously intermittently used several different machines.

A key part of achieving the speed required to make one multi-purpose machine suitable is the ability to automatically change its cutting tools to optimise throughput. The tool is held by a spring-loaded collet which is actuated by a central drawbar that runs the length of the spindle. Once the tool to be changed is moved to its designated position in the machine’s tool-storage magazine, an actuator pushes the drawbar forward to disengage the collet and release the tool. The spindle then moves to the location of the new tool in the magazine and the process is reversed.

From time to time, the collet may fail to retract fully, preventing the new tool from engaging completely. Failing to detect and rectify the problem could cause expensive damage to the tool, the workpiece and possibly the spindle. Continex’s inductive sensors are trusted to provide robust detection of incomplete tool engagement in what is already a tightly packed assembly.

Contrinex is renowned for the robustness of its ‘Extreme’ ‘700 Series’ of inductive sensors, and this is also an option within Contrinex’s smart inductive sensor portfolio. Therefore, a single, robust, stainless-steel-cased smart inductive sensor is embedded radially into the body of the spindle, immediately adjacent to the rear of the drawbar.

The sensor is a high-precision digital distance-measurement smart sensor, also known by the acronym of ‘DMS’. It measures the distance to a longitudinally inclined face at the end of the circumference of the drawbar. Therefore, as the drawbar moves forward, the distance to the slope of the inclined faces changes in direct proportion to the distance the drawbar moves.

Lateral position measurement derived from an inclined plane is just one application for precision measurement sensors. In this application the sensor provides a sensing distance of up to 6 mm and a dynamic resolution of ±5.5 micrometres, delivered in a highly accurate 16-bit digital output, which determines the drawbar’s position in real-time.

The machining centre initially calibrates the two extremes of the drawbar travel and these are recorded in the sensor’s local data store. Thereafter, the sensor operates in two distinct modes: During tool changes, the drawbar position is monitored in real-time, ensuring that its motion follows the expected pattern; once the extreme of travel is reached in either direction, the sensor de-energises the actuator and initiates the next stage of the process. Any non-compliant measurements stop the process and trigger an alarm.

Contrinex smart sensors are designed with the needs of OEMs and system integrators in mind, providing fit-and-forget solutions. On-board data storage holds cumulative operating data for user-specified purposes, including predictive maintenance whilst continuing to offer reliable, cost-effective and compact solutions that deliver ultimate peace of mind.