1-Trak provides a flexible high performance solution to tool changing problems

Task
Tool changing devices for CNC machines enable rapid transfer of tools in and out of the machine and are available in standard format with either a circular carousel or oval track the most common configurations.

However, when Walter Maschinenbau wanted to develop a new CNC controlled Helitronic tool grinder they needed a product that could link 12 or 24 x 254mm diameter grinding discs and traverse them around a circuit without them clashing. In principle this did not sound too demanding until the space available to fit the tool changer into was revealed.

With no suitable solution evident Walter turned to linear motion experts HepcoMotion to see if a standard PRT2 track system could fit into the limited available space. Initial investigations were promising but the aspect of preventing the discs clashing as they went around the curved sections of the track was proving challenging. The obvious option of just lengthening the track was not possible with the space available. There was also the requirement for the control system to be able to demand any wheel in the circuit and bring it to a predetermined position within a positional accuracy of 0.050mm.

Solution
After discussing the key requirements with engineers from HepcoMotion the 1-Trak system began to look like a viable solution as the product would allow any two dimensional track shape to be produced. Whereas PRT track systems have standard end segments of the same diameters linked by straight slides, 1-Trak allows a bespoke shape to be produced. Fitting into the available space and preventing the discs from clashing meant a number of hours using CAD software, developed by HepcoMotion, to plot the required circuit for the discs.

The final shape for the 12 and 24 carriage systems, to prevent the discs from clashing, was somewhat different as the same length space restrictions existed in the machine for both options. In the 24 carriage case there was vertical room available and this was utilised by the final C shape of the system.

Achieving the required accuracy
To achieve the motion around the track with either 12 or 24 carriages there would need to be a small amount of clearance at each link attachment; this potentially could have been problematical in achieving the positional accuracy tolerance of 0.050mm. This tight tolerance was necessary to ensure the shaft holding the disc was not damaged when it was returned to the holder on the tool changer.

Result
The joint cooperation between HepcoMotion design team and Walter development engineers produced a unique solution to a challenging problem. The 1-Trak system provides a smooth, quiet robust solution that, following rigorous testing, has proved to be highly reliable. The ease of installation coupled with the ability to achieve the positional accuracy in such a confined space has opened up opportunities for similar solutions on a smaller or larger scale.

Link to Video: http://youtu.be/FSbKCZ_VrIU