WHAT DOES A TYPICAL 3D PATH-PLANNING SYSTEM ENTAIL?
Dave and Khaled • Renishaw: Typically, a 3D path-following system consists of:
A mechanical moving part, which usually carries a cutting tool or measurement sensor to its required location through a pre-specified path
An electrical/electronics power stage including an actuator (motor), which transforms electrical energy into mechanical energy, and a power amplifier to make sure the motor gets the right level of electrical energy
Software that orchestrates target paths, follow through, feedback, and correction, to ensure application requirements are met
Depending on application requirements for speed and accuracy, and given the constraints of cost, time, and available expertise, the main system constituents will gain more or less importance in terms of the functions they perform. Some functions could even migrate from one constituent to another. As an example, one could replace a tachometer (electromechanical system) by an estimation algorithm (software). In some cases, more physical axes are required to achieve speed, accuracy, and application-specific requirements.
Steve • Siemens: The performance and sophistication of 3D path-following systems depends on application requirements. Performance level and the need for total system design increases as process requirements demand ever more challenging specifications for:
High velocities along the 3D path
Increased geometric accuracy
Smooth path profile (minimization of geometric and velocity oscillations)
In a machine tool application, for example, this helps product manufacturing meet demanding tolerance, surface finish, and cycle time specifications. To achieve the highest standards, a systems design approach is needed. Critical system components include: a motion controller with advanced trajectory planning and interpolation algorithms; a mechanical system design that carefully considers structural dynamics; high performance motor and drive systems; controller algorithms that directly address machine dynamics and effectively model and correct for machine kinematics errors; and software tools to automate the controller setup and optimize the system with regard to the mechanical aspect.
WHAT ARE THE MAIN CHALLENGES WHEN IT COMES TO IMPROVING 3D PATH-FOLLOWING PERFORMANCE?
Dave and Khaled • Renishaw: The main challenge is to reconcile speed and accuracy at an affordable cost. This is an optimization exercise where speed and accuracy are known to be antagonistic and constituting a zero sum system. To reconcile these two, the technical challenge is that it requires the electromechanical system to have a high bandwidth, in that it is able to respond to demands by software. However, this needs to be achieved while keeping costs down so that it is affordable — this is the economic challenge.
Steve • Siemens: The more demanding the requirements, the more necessary it becomes to adopt a systems approach. What makes it difficult, however, is when different components are developed by different teams or companies.
One of the challenges is to synchronize improvements of all system components. When components come from multiple companies, it's essential for all parties to participate in the design phase to optimize machine dynamics relative to requirements. Simulation tools are especially helpful here because they provide a common environment that identifies the most critical components and functions in a system.
WHAT IS THE MOST SIGNIFICANT ADVANCE IN 3D PATH FOLLOWING IN THE LAST FIVE YEARS?
Dave and Khaled • Renishaw: In our case, we've developed a head that fits to the quill of CMMs and has a greater bandwidth than the CMM itself; consequently, it is capable of accurately following the required software path at high speeds.
Steve • Siemens: The most significant advance is in the area of high fidelity simulation. This means simulation of dynamic systems, path planning and interpolation, control algorithms, and setup automation.
Software connecting different simulation pieces into user interfaces allows rapid iteration through varying simulation conditions and analysis of 3D path-following results. Simulation helps system designers identify critical components for a given application and validate 3D path accuracy against known requirements.
WHERE DOES THE GREATEST OPPORTUNITY LIE TO IMPROVE FUTURE PERFORMANCE BASED ON INTERDISCIPLINARY OPTIMIZATION?
Dave and Khaled • Renishaw: System integration. The quality of integration is key to the system working together properly. Knowledge of system constituents is important and necessary, but knowing the strengths, weaknesses, what each constituent can do, and what is best done by one rather than the other is what makes the difference. This, inherently, is part of the optimization exercise performed by system designers.
Steve • Siemens: First is to continue to use simulation to better understand challenges and identify critical areas. The issue of know-how sharing and consulting with machine builders requires creative ways of providing support services. Control vendors have begun to offer web-based support services to their motion control users.
These services include automated assessment of machine performance, such as modeling machine dynamics based on measurements of the machine doing a pre-configured “exercise routine.” The service can flag performance degradation as assessments are taken periodically and automatically. Future web-based services could include online collaboration of system design and simulation.
HOW CAN DESIGNERS BETTER PREPARE THEMSELVES TO DEAL WITH THE CHALLENGES OF INTERDISCIPLINARY OPTIMIZATION?
Dave and Khaled • Renishaw: Designers need to always allocate time for learning. This has different aspects, including knowledge acquisition in the field of specialization, in related fields that are both system and application-dependent (mechanical, electrical, and software for system-related knowledge), and in unrelated fields, to aid innovation.
Designers need to consider the speed at which new technologies are evolving and how to acquire knowledge about them accordingly. They need to be willing to get out of their comfort zone and challenge themselves to acquire valuable knowledge and experience.
Steve • Siemens: The common engineering principles required for designing a high performance system integrating controls and mechanics are an understanding of dynamic systems and software skills. A strong foundation of engineering skills in differential equations, linear algebra, system modeling, and simulation are essential prerequisites for system designers.
Another area that allows system designers and system components to effectively communicate concepts among themselves is object-oriented design. Use of standards such as UML should be encouraged even among team members who are not traditionally software developers. A systems design approach ultimately requires identification of components, their properties and behaviors, and opportunities for component reuse.
For more information on mechatronics, visit motionsystemdesign.com's Knowledge FAQtory and look for links to related articles and information.
Meet the experts
Dave Wallace and Dr. Khaled Mamour
Siemens Energy and Automation Inc.