Clamp Control of Tools and Workpieces

In Metalworking, the clamping status of tools and workpieces are monitored in many applications. Typically, inductive sensors are used to control this.
Three positions are usually detected: Unclamped, clamped with object, and clamped without object. The sensor position is mechanically adjusted to the application so the correct clamping process and clamping status is detected with a proper switch point. Additionally, with the usage of several sensors in many cases the diagnostic coverage is increased.
For approximately 15 years, inductive distance sensors with analog output signals have been utilized in these applications with the advantage of providing more flexibility.
 By using a tapered (conical) shape, an axial movement of the clamping rod can be sensed (as a change of distance to the inductive sensor with analog output). Several sensors with binary (switching) output can be replaced with a sensor using such a continuous output signal (0..10V, 4-20 mA or e.g. IO-Link). Let’s figure a tool in a spindle is replaced by another tool with a different defined clamping position. Now, rather than mechanically changing the mechanical position of the inductive sensor with binary output, the parameter values for the correct analog signal window are adjusted in the control system. This allows easy parameter setting to the application, relevant if the dimensions of the clamped object may vary with different production lots.
The latest state-of-the-art sensor solution is the concept of a compact linear position system which is built of several inductive sensor elements mounted in one single housing. 

Instead of a tapered (conical) shape, a disk shaped target moves lateral to the sensor. From small strokes (e.g. 14 mm) up to more than 100 mm, different product variants offer the best combination of compact design and needed lateral movement. Having data about the clamping force (e.g. by using pressure sensors to monitor the hydraulic pressure) will lead to additional information about the clamping status.
For more information on linear position sensors visit www.balluff.com.
For more information on pressure sensors, visit www.balluff.com.