In-house designed and built motion control components are used to design and build a high-precision motion stage.
In many specialized manufacturing operations, precision is non-negotiable. Yet, at the same time, many system designers and integrators are also being challenged to increase performance and reduce costs.
To meet the dual demands to increase performance and lower costs, Prodrive Technologies has developed a portfolio of high-precision motion components that are off-the-shelf. This new line of products is specifically designed with advanced technologies to help meet the demands of high-performance motion applications. It’s also designed to keep costs under control and make it possible to easily select and combine the right products for the specific application’s requirements.
As an example, the company recently developed a high-precision stage known as the Proton Motion Stage. The stage combines a range of off-the-shelf components, designed and manufactured in-house, to meet the requirements of high-precision and reliable measurement inspection applications, such as those involving scanning electron microscopes or wafer inspection.
One thing that makes the new stage stand out compared to other motion stages is the modular and scalable approach to the design, which also simplifies the process of bringing solutions to market. “In the past, businesses would create a motion stage by sourcing the different elements from various suppliers and attempting to combine them for their requirements,” explains Milan van den Muyzenberg, Technical Director for Prodrive Technologies Motion & Mechatronics program. “Our solution has been designed to provide a ‘one-stop shop’ instead, helping to speed up the time to market.”
Because all of the components are manufactured by one source, they are designed to be integrated and work seamlessly together. For example, every drive is optimally designed to work with the actuators and every part of the stage can communicate accurately with the master controller. What’s more, these components can also be effectively combined with products from other manufacturers, if and where required.
Tried and true building blocks
Each application has different system requirements, from velocity, stroke, and accuracy, to throughput. A fully configurable solution, where one can develop a motion solution by picking and choosing the specific products required, has clear benefits.
The Proton Motion Stage is scaled to specific requirements using off-the-shelf components as its building blocks. It can even provide a high-accuracy option for those specifying systems for vacuum compatibility, where in the past there has been far less choice compared to stages suitable for atmospheric operation.
With conventional motion stages that apply cross roller bearings and appropriate pre-loading, interference can be an issue as a result of temperature changes which can cause variations and negative effects on friction. The new stage is uniquely built with statically determined pre-loaded mechanisms to ensure that interference has a limited effect on motion performance. A number of off-the-shelf components were used in its construction, including linear actuators, servo drives, motion controllers and more, including a motion software platform with real-time performance and tooling. Below we’ll look at how each of these components contributes to the overall design of the motion stage.
Highly efficient motion without contamination
A bad actuator in a motion stage has the potential to result in bad yield, poor accuracy, low performance, and reduced throughput. In vacuum stages, it’s also critical that particles from the actuator do not ‘leak’ or cause out-gassing into the environment. In other words, clean operation is vital. Another challenge is that there is no air to dissipate heat within the vacuum environment, meaning that heat must therefore be transferred differently.
The company’s Gryphon linear actuator series features ironless linear motors that were designed to manage thermal challenges by transferring heat via the metal part of the coil unit. This provides reliability, preventing system failures. In precision applications, such as semiconductor inspection, failure of a part such as a linear motor can have a big impact on operations.
“If a motor phase were to stop working, the whole stage could potentially need to be disassembled and reassembled by a skilled worker, taking valuable time,” says Bart Gysen, Motors Product Line Manager for Prodrive Technologies. That’s why the company has invested in the design and testing of the Gryphon linear actuators specifically to reduce the chances of these sorts of issues arising on site.
Vibration isolation for high positioning accuracy
The company’s Iris actuator is another vacuum-compatible component available off-the-shelf. Six of these limited stroke voice coil actuators are included in the Proton Motion Stage, providing active vibration isolation. This eliminates the disturbances that could disrupt high positioning accuracy. These could include external disturbances and the forces created by the components of the motion stage itself.
With an understanding of each of the components that comprise the motion stage, the company has been able to accurately identify the forces caused by other parts of the machine and reduce the amount of vibrations accordingly, which is also easily adjustable via the control software.
What’s more, the design of the stage takes into account the potential disturbances that the machine could also cause to its own environment and has been designed to eliminate these vibrations as much as possible.
Drives that reduce drift
Drives drift over time. So, when a setpoint is being requested, it will eventually deviate, taking longer to correct, and negatively affecting performance. In a metrology application, this can be problematic, as accuracy, repeatability, and speed are all needed when moving between positions.
The new stage is designed with drives such as the company’s Apogee and Kepler series drives. These feature low drift components and specially designed voltage reference and custom current sensors, which compensate for drift issues.
Most drives are built with a focus on automation applications, rather than the high-performance environments found in semiconductor applications. However, because every part of the Proton Motion Stage is produced in-house, there is much more control over all of the variables involved. With a greater focus on components that reduce drift and deliver high linearity, the drive can enable high dynamic performance within a motion stage.
What’s more, these drives also feature low noise, ensuring no additional disturbances are introduced into the system. This eliminates jitter, which could cause inaccuracy, and enables applications to move at specific velocities without being impacted by noise and disturbances. This is essential in scanning applications, for instance.
The drives also feature a high switching frequency which provides high bandwidth and good attenuation for external disturbances. Internal filtering also limits disturbances to other systems like external sensors which can be extremely sensitive to noise in high-precision applications.
Real-world motion control
Another integral part of the Proton Motion Stage is the motion controller. The Poseidon motion controller works with the Prodrive Motion Platform (PMP) to collect sensor data and then communicate seamlessly with the servo drives to determine new position setpoints.
The motion controller features multiple EtherCAT buses which help to reduce the delay between the motion controller and the servo drives. Combined with the controller’s multi-core x86 processor, this shortens the amount of time needed to collect sensor values, calculate new setpoints, and communicate these back to the drives. The faster this process, the more it can help improve the overall performance of the motion stage.
The PMP motion control software, with real-time performance and tooling, runs the algorithms required for motion control. However, it also provides extensive simulation capabilities. The PMP integration in Simulink lets engineers generate ready-to-load binaries, which can be loaded into the system easily, without requiring a specialist software engineer.
The big benefit of simulation is that the stage’s processes can be tested even without the hardware in place to verify that it’s working. Optimization of the hardware or control of the system, and the impact of any changes to them, can then be captured at this early stage, making it quicker when the time comes to complete testing with the hardware.
However, this approach is also beneficial for saving businesses development time and money. There is no need for a dedicated software engineer to code the algorithms, as there are customizable examples that users can simply adapt, and then test and re-test as needed. The PMP can implement a control algorithm code, generated from Matlab/Simulink, and run it with each EtherCAT cycle.
The next step in customizing motion stages
In the future, it will also be possible for motion applications to specify an off-the-shelf Pinpoint laser interferometer. This provides a high accuracy, vacuum-compatible solution which enables position measurement directly, or closely to, the point of interest.
Just like most interferometers, Pinpoint delivers on high resolution and reliability. However, it has a unique design featuring a DFB laser which extends its lifetime. Instead of requiring replacement every few years, Pinpoint will last for more than ten years, usually outliving the lifetime of the system itself. This reduces maintenance requirements, as well as replacement and service costs.
Pinpoint also excels with absolute position measurement. This technique is used instead of the homing process and takes as little as 20 seconds to complete. The result is that from that point, the interferometer will always precisely measure the exact same location, reducing manual interventions needed. Even if the machine is turned off and on again or moved, these settings are easily and quickly recovered, saving time.
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