Robust inductives stop high-speed spindles ‘getting in a spin’

To maximise their efficiency and productivity, high-speed machining centres often include automated tool changers. When a drive-motor manufacturer needed a reliable and robust sensor to detect the position of a machine’s main spindle before initiating the tool-change sequence, it turned to Contrinex.

Contrinex’s miniature inductive sensors were selected to detect the position of a slotted centring disc mounted on the motor shaft because of their exceptional repeatability and positional accuracy better than 0.01 mm.

Modern machining centres execute multiple metal-cutting operations within a single machine, often deploying a separate tool for each operation. Automated tool changes remove labour and reduce the non-productive time needed to change tools, improve efficiency and machine utilisation,

After completing a machining operation, the main spindle of the machine comes to rest and a sensor confirms that it has reached the null position. This is the point at which the tool can be disengaged completely and is safe to initiate the tool-change sequence.

Exceptional accuracy and repeatability are required to sense the position of a shaft previously rotating at up to 14,000rpm. A robust and reliable solution to detect the null position is needed to prevent damage from occurring.

Space constraints require the sensor to be no larger than Ø5mm, but capable of withstanding mechanical shock, and high levels of vibration. The sensor is also likely to be covered in oil due to its location detecting the position of a slotted centring-disc mounted on the drive motor shaft.

Contrinex inductive sensors are designed to ensure long-term reliability and repeatability in demanding environments and this is also true of the sensors from the company’s extensive Miniature range. An M5 embeddable inductive sensor, constructed from V2A / AISI 303 stainless steel with a PPE sensing face and hermetically sealed cable entry was selected.

The 25mm-long sensor is embedded directly in the wall of a rotary-encoder housing fitted to the drive-motor shaft. Its sensing distance of 0.8mm eliminates the risk of accidental collision with the spinning disc. The required angular resolution translates to a positional accuracy of better than 0.01mm.

The sensor’s vacuum-encapsulated electronics ensure resistance to shock and vibration, and no additional electrical or mechanical protection is required. Fit-and-forget operation keeps maintenance requirements to a minimum, overcoming the mechanical fragility of alternative optical-sensing encoder technology. The sensors are configured with an industry-standard PNP normally-open interface, connected to the customer’s control system via a flexible, oil-resistant PUR sheathed cable.