Software and innovation, simplified

Sept. 1, 2009
Using the right software means easier motion control and application development.

Intense global competition is pressuring machine builders to deliver equipment that increases throughput and features while reducing operating costs. Rising energy costs and environmental awareness are prompting engineers to design for lower energy consumption as well. In one approach, some of today's equipment builders have switched from designing single-purpose machines to creating flexible and effective multipurpose devices — by adopting modern control systems and sophisticated algorithms, and integrating high-end electronics into mechanical structures.

Figure 1

Hardware and protocol innovation

Motion control is critical to these mechatronic systems, particularly where many mechanical parts are substituted with electronic solutions. One example is the elimination of rigid shafts to perform camming operations. In some machines, these shafts are replaced by a combination of drives and motors that rely on control software to provide camming functionality. The machines are mechanically more flexible, easier to maintain, and smaller. However, caveat emptor: These machines also contain more numerous electronic components and require complex control. Design of these sophisticated machines is also challenging because it requires multidisciplinary knowledge and collaboration between different design groups. Implementation of motion tasks, in particular, increases design complexity.

Helpful here are advanced microchip designs, increasingly compatible communications protocols, and the control design and system-implementation software that we will discuss in a moment.

Design for required motion

Because motion components are central to machine operation, control systems must tightly integrate with automation components — including controllers, human-machine interfaces, I/O equipment, and even specialty cameras and sensors. Three newer technologies are facilitating this higher integration:

  1. Over the last couple of years, field-programmable gate arrays or FPGAs and powerful commercial processors have found their way into industrial platforms. Combined with reliable real-time operating systems, they offer the performance and flexibility needed to control modern machines.

  2. Get it right the first time

    Digital drives that use deterministic communication protocols and buses to communicate with motion controllers offer an alternative approach to centralized solutions.

  3. Standards organizations and committees harmonize the access of motion control functionality across different platforms. Through development of its Motion Control Library, PLCopen provides a standard that defines reusable components. This reduces the hardware dependency of motion applications, increases the reusability of software components, and allows control engineers to adapt their knowledge when they switch between tools of different vendors.

Figure 2

Software leverages and integrates these new tools while providing a helpful level of abstraction. To illustrate: Many engineers don't want to deal with low-level signaling for motors or create algorithms to control motor-coil energy flow. Instead, they want to design systems based on the ultimate functions that perform different move types — such as straight lines, arcs, or contoured moves — and use tools (rather than brute calculations) to synchronize multiple motors through their gearing and camming functions. Software fits the bill by combining different functions and defining the sequence in which they are executed: System motion profiles are entered into the software, which then generates the trajectories to execute the exact movements and positioning of coordinated motion axes. Tasks like supervisory control or spline interpolation for smooth motion are provided through a higher-level motion engine.

New tools for graphical motion application development

This high level of abstraction simplifies the design of standard motion control applications and enables control engineers to realize multi-axes linear motion applications within minutes. Even so, there are many situations that require lower-level access to control algorithms or I/O channels as well. For these application algorithms, such as field-oriented control or kinematics, some motion control software tools also provide an interface that allows engineers (and scientists) to customize individual components and solve nonstandard cases.

Based on standards, some software can even resolve motion integration challenges, so developers can focus on the design and validation of motion profiles. By providing direct access to high-performance embedded systems, these tools enable the development of custom motion control systems.

Where early motion system development is important, look for software that allows virtual prototyping. Digital prototypes add value to designs — allowing mechanical engineers to develop efficient systems in which motor and actuator size are perfectly matched with the requirements of the mechanical structure.

Traditionally, engineers chose motors based on limited information and then over-engineered the motors by adding security margins. To help with this approach, most motor vendors provide tools for choosing a motor to fit a specific need. However, the information those tools require is difficult to gather, as the mathematical formulas describing dynamic systems are complex.

Digital prototyping tools allow simulation of the entire system's dynamic behavior in advance, including the motors and even the control algorithms. By applying realistic motion profiles to the simulation, designers can gather all the necessary information to size motors and specify mechanical components. From there, control engineers can start developing the motion application as soon as the 3D CAD model is available, and provide valuable information to mechatronics engineers before they start building physical prototypes. This approach allows control and mechatronic design teams to work in parallel and collaborate on the design of the mechatronic system.

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One newer software module from National Instruments, Austin, Tex., called LabVIEW NI SoftMotion Module, offers graphical development for custom motion control applications. The tool provides a complete motion solution for high-performance embedded systems, incorporating new technologies like FPGAs, real-time processors, and support for industrial communication protocols like EtherCAT.

For motion application development, it provides a graphical interface to configure and test settings and parameters for motion axes, including encoders and motion I/O within a project environment. When the hardware configuration is complete, an interactive test panel lets engineers validate the configuration and move individual axes to verify the hardware setup. NI SoftMotion also allows programming of motion profiles with a high-level function block application programming interface (API). These function blocks are designed for use in real-time applications and can publish parameters as shared variables for both HMI programming and status monitoring. Industrial function blocks (familiar to many control engineers) can be combined with existing virtual instruments (and functions) in LabVIEW for custom industrial measurement and control applications.

In addition, configurable straight-line and arc-move function blocks allow engineers to easily define motion profiles for Cartesian motion systems. For motion profiles that cannot be defined by a series of straight line and arc moves, contour moves offer additional capabilities. (A contoured move is expressed as a series of points that the motion controller uses to extrapolate a smooth curve. These points are usually generated with the help of a CAD environment or graphics program and are stored in spreadsheet or text form.) The NI SoftMotion module also includes advanced functions for custom motion application design including trajectory generation, spline interpolation, position and velocity control, and encoder implementation. Most of these elements offer an interface for control engineers allowing full customization. This lets designers add advanced control or specialty I/O if their motion applications have advanced requirements.

For motion profile validation, the new software provides integration with the DS SolidWorks 3D CAD environment, allowing engineers and scientists to create digital prototypes of their Cartesian motion systems. By applying the motion profile developed with NI SoftMotion function blocks to a simulation-ready 3D CAD model, engineers can evaluate and validate the operation of moving parts and determine whether the motion profile performs as expected. Digital prototyping helps engineers see how various components interact and validate their motion profile without the risk of damaging physical components. Finally, it allows virtual exploration of products before finalization — by both engineers and potential end users.

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