Smart inductive sensors prevent incomplete engagement during automatic tool changes for compact machine-tool spindles


Smart inductive sensors prevent incomplete engagement during automatic tool changes for compact machine-tool spindles

Modern CNC machining centers cope with ranges of materials, workpieces and cutting speeds that require different tool characteristics; spindles with automatic tool-changing are key to optimizing throughput. If a new tool fails to engage completely, damage to the tool, the workpiece or the spindle results. Designers specified Smart Sensors from Contrinex, embedded in the body of the spindle, to monitor the position of the tool during changes; any noncompliant measurements stop the process, triggering an alarm.

Customer Values

  • Embeddable inductive Smart Sensor monitors drawbar position, detecting incomplete tool engagement and inhibiting further motion before damage occurs

  • Single-sensor positional-control system is non-complex and highly affordable

  • Embeddable M12 sensor fits snugly in the limited space available

  • Industry-standard IO-Link connectivity provides a single interface to the machine control system

  • Cumulative operating data for predictive maintenance, including temperature and operating-cycle count, is recorded in on-board data storage

  • Sensor configurations are stored locally, allowing plug-and-play replacement of sensors when needed

  • Proven technology ensures highly reliable fit-and-forget operation with no manual intervention

Specific Product Advantages

  • Robust, metal-cased inductive Smart Sensors are ideal for easy integration
  • Multi-channel monitoring circuitry allows users to define up to 16-bit customized output thresholds
  • Sophisticated sensing electronics deliver dynamic linear-distance measurements with a resolution in the micron range
  • High-speed device-to-device communication enables decentralized data-processing and decision making
  • Dedicated service-data blocks hold device-specific data including product ID, location and serial number
  • Visible LED indicators enable sensors to self-identify on demand, simplifying commissioning and trouble-shooting routines
  • Industry-standard -25°C to +70°C operating range

Customer Application

 Modern machine-tool spindles offer CNC machine designers huge flexibility, enabling individual machining centers to cope with ranges of materials, batch sizes, workpieces, 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 optimizing 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.

Customer 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 micrometers, 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-energizes the actuator and initiates the next stage of the process. Any noncompliant 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.