SmarTemp – Development of smart equipment based on deformation sensors for the automatic correction of thermal errors in machine tools

The ever-higher expectations of productivity and precision in the metal-cutting industry over the past 20 years have led to an urgent need for more dedicated and intensive research into viable means for correcting thermo-elastic errors in machine tools. It is estimated that up to 75% of geometrical workpiece errors can be traced back to thermal issues in the original machine tools.

The countermeasures used most frequently in the industry include the thermally stable design of machine tools, specified warm-up procedures, thermal conditioning by cooling systems, and air conditioning of the production environment. However, while thermally stable machine tool design can reduce the overall effect of temperature gradients, it cannot eliminate all thermal errors.

By contrast, mechatronic correction promises good results for several modeling techniques. This approach to error correction relies on the machine controller to add a degree of offset to the machine tool’s current position on its working axes. The right amount of correction is modeled on the basis of current sensor data.

The most forward approach is to measure the TCP (Transmission Control Protocol) displacement directly. The advantage of this method is that it avoids a reliance on models. However, the resulting values are only valid at the time of the measurement. Indirect correction can solve this issue by using machine state variables like temperatures, machine control data, or deformation. The SmarTemp project focuses on the novel concept of using integral deformation sensors (IDS) to collect more information with less installation and computational efforts required.

General Goals the SmarTemp Project is Pursuing

The SmarTemp project will contribute to the further development of the IDS technology in the following areas:

• Assessing the reliability of online correction functions under real cutting conditions.
• Validating the online correction function for machining centers across multiple processes. For example, different directions are critical both in milling and in boring. Since a machining center is designed to do both, the IDS sensors should be installed in a way that can predict the thermal error for both processes with high accuracy.
• Validating the online correction function for five-axis machines. Since rotary axes must not be neglected in terms of their thermal behavior, the IDS sensors should be developed further to also detect significant errors on these axes.

The Specific Role of Wibu-Systems

In the SmarTemp project, the knowledge and competences contributed by Wibu-Systems focus primarily on the provision of cybersecurity components to be integrated into the proposed automation framework (Beckhoff TwinCAT). This covers the following major activities on the project:

• Developing a data protection concept for a specialized “technology data market platform” to act as an advanced machine technology data exchange, consisting of a sensor data collection system and a data provisioning system for the advanced machine technology data generated by a “digital twin” of the given automation equipment.
• Introducing and developing new prospects for novel business models based on the ownership of the data produced and gathered by designing a digital data trading place, including Wibu-Systems’ CodeMeter licensing capabilities for protected software and data. This also provides a means to enforce system integrity and IP (Intellectual Property) protection throughout the data trading system.
• Developing the architecture of the IT security system and the automation infrastructure to set up the digital data marketplace.
• Refining and integrating the CodeMeter hardware and software components into the automation equipment (industrial PCs).
• Integrating CodeMeter licensing and key management for securing the networking nodes within the infrastructure; ensuring secure endpoint communications through a certificate und key storage (container) API for industrial protocol stacks (i.e. part of OPC UA Client Server architecture or other communication protocols).

The specifications for these development activities and the eventual deployment of the protection schemes for automation and infrastructure devices will be in accordance with the ISO IEC/ISA-62443 standards.