Published: Sep 14, 2026 · Source: Instrumentation Monthly
Within an automatic tool-changing spindle, a spring-loaded collet retains the cutting tool in position. The collet is actuated by a central drawbar running through the length of the spindle. During a tool change sequence, an actuator moves the drawbar along its axis, releasing the current tool before allowing a replacement tool to be clamped securely.
For the process to operate reliably, machine control systems must be able to verify several critical drawbar positions, typically:
Failure to accurately detect these positions can have significant consequences. If a collet fails to retract fully or a tool does not engage correctly, machining may commence with an improperly secured tool. The resulting damage can affect the tool, the workpiece and, in extreme cases, the spindle itself.
As spindle assemblies become increasingly compact, manufacturers require robust and fail-safe monitoring solutions that can be integrated without increasing system complexity.
Traditionally, the three operating states of a spindle drawbar are monitored using three separate switching sensors positioned at different locations within the spindle assembly.
While functional, this approach presents several challenges:
For machine builders, each additional component represents both a design consideration and a potential point of failure. In high-performance machining applications where reliability and repeatability are paramount, simplifying the sensing architecture can deliver significant operational benefits.
The new Contrinex Travel Sensor has been developed to replace traditional multi-sensor arrangements with a single intelligent sensing device that monitors the full drawbar movement range.
Installed radially within the spindle body, adjacent to the drawbar, the embeddable 15 x 25mm sensor serves as a high-precision distance-measurement device. Its target is an inclined surface machined onto the circumference of the drawbar. As the drawbar moves, the distance between the sensor and the target changes proportionally, allowing the sensor to determine the exact drawbar position in real time.
With a sensing range of up to 20 mm, the sensor provides highly accurate 16-bit digital measurement data. This enables continuous monitoring of drawbar travel, rather than simple on/off position detection, giving machine builders access to significantly richer process information.
One of the key advantages of the Contrinex Travel Sensor is its ability to digitally define multiple switching points.
During commissioning, the drawbar positions corresponding to the required operating states are recorded within the sensor. Users can then configure up to three switching points to represent:
By replacing mechanical sensor adjustment with digital teaching, installation becomes faster, more repeatable and less dependent on manual fine-tuning. The approach also reduces setup time for OEMs while simplifying future maintenance and replacement procedures.
Configuration is performed using Contrinex’s PocketCodr tool, enabling rapid parameterisation and straightforward commissioning..
Beyond simple position detection, the Contrinex Travel Sensor continuously monitors drawbar movement throughout the entire tool-change cycle.
During operation, the machine control system can verify that the drawbar follows the expected motion profile. Once the programmed end position is reached, the sensor can trigger the next step in the sequence, helping optimise tool-change efficiency.
If a measurement falls outside acceptable limits, the control system can immediately halt the process and raise an alarm. This proactive approach helps prevent costly crashes, protect spindle components, and reduce the risk of producing defective parts.
The ability for the Contrinex sensor to continuously monitor movement, rather than simply detect end positions, represents a significant advancement in spindle condition monitoring and process security.
Like all devices within the Contrinex Smart Sensor portfolio, the Travel Sensor incorporates integrated IO-Link connectivity as standard.
This provides machine builders and end users with a number of benefits, including:
On-board data storage enables the collection of cumulative operating data, allowing users to monitor trends, identify emerging issues, and schedule maintenance activities more effectively.
By replacing three conventional sensors with a single digitally configurable device, the Travel Sensor delivers several tangible advantages:
For OEMs, this translates into a more streamlined machine design and lower build costs. For end users, the result is improved uptime, enhanced process reliability and greater confidence in tool-change performance.
Contrinex’s UK distributor is PLUS Automation.
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Source: Instrumentation Monthly · Original article: Contrinex’s new smart spindle position sensor simplifies drawbar monitoring in CNC machine tools