Contrinex smart inductives ensure safe tool changes on compact machine-tool spindles

CNC machining centres use automatic tool-changing spindles to rapidly switch between different tools with characteristic suited to different materials, workpieces and cutting speeds.

To ensure that a new tool engages completely and to prevent damage to the tool, the workpiece or the spindle, designers specified Contrinex’s NEW SMART inductive sensors. Embedded within the body of the spindle, the sensor monitors the position of the tool during changes, so that any non-compliant measurements stop the process, triggering an alarm.

Application

Modern machine-tool spindles offer CNC machine designers huge flexibility, enabling individual machining centres to cope with ranges of materials, batch sizes, work-pieces, tools and cutting speeds that might previously have needed several different machines. Successive cuts often call for different tool characteristics, spindles with automatic tool-changing are key to optimising throughput.

A spring-loaded collet, actuated by a central drawbar that runs the length of the spindle, retains the tool in position. 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 along its axis until the collet disengages, releasing 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 leads to expensive damage to the tool, the workpiece and possibly the spindle. Spindle manufacturers require a robust, fail-safe method of detecting incomplete tool engagement in what is already a tightly packed assembly.

Solution

Designers specified rugged inductive sensors from the Contrinex Smart Sensor portfolio; a single metal-cased sensor, embedded radially in the body of the spindle immediately adjacent to the rear of the drawbar, performs the required tasks. All Contrinex Smart Sensors feature IO-Link connectivity, providing a single, industry-standard interface to the machine control system.

The sensor operates as a high-precision distance-measurement device; its target is a longitudinally inclined face on the circumference of the drawbar. As the drawbar moves forward, the distance to the inclined faces changes in direct proportion to the distance moved. With a sensing distance of up to 6 mm and a dynamic resolution of ±5.5 micrometres, the sensor delivers a highly accurate 16-bit digital output, enabling the drawbar position to be determined in real-time.

At the time of initial calibration, the drawbar positions corresponding to the two extremes of travel 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 inductive Smart Sensors are designed with the needs of OEMs and system integrators in mind and provide an unobtrusive fit-and-forget solution. On-board data storage holds cumulative operating data for user-specified purposes, including predictive maintenance. These highly versatile sensors meet designers’ needs for a reliable, cost-effective and compact solution that delivers ultimate peace of mind.

PLUS Automation aims to help you #MAKESENSEOFSENSORS, helping solve applications, improve machine performance and reliability, and reduce costs using Contrinex’s exceptional choice of sensors. Find more information and read other application examples go to www.PLUSAx.co.uk

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