The manufacturing landscape is undergoing a transformation, propelled by the need for innovative, efficient, and precise technology that can effectively replace expensive manual labor. This article examines advancements in Flexiv’s material abrasion technology, specifically focusing on sanding and polishing applications and the utility of force control technology.
The Unseen Hero: Precise and Durable Force Sensors
One of the hallmark features that empowers the automated material abrasion process is force sensors. Typically integrated into end-of-arm sanding tools on traditional collaborative robots, they provide the robot with the ability to feel the surface it is interacting with and adjust the force it impacts to the workpiece accordingly.
Adaptive robots use the same basic technology, but instead of only using an end-of-arm force sensor, they use precise torque sensors which are embedded in each of an adaptive robot’s seven degrees of freedom, along with a force sensor at the end of the arm. This configuration enables the processing of force data from multiple inputs, offering a more detailed and nuanced understanding of how the end-of-arm tooling is interacting with the workpiece.
This is only possible thanks to the development of proprietary displacement sensing technology that provides adaptive robot operators with two essential advantages:
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Stability and Accuracy: Resistance to thermal drift provides improved precision.
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Durability: Designed to accommodate millions of overloading cycles, the sensors are industry ready.
Compared to conventional strain gauge transducers, these critical characteristics ensure reliable performance, even when faced with thermal contraction and expansion fluctuations that traditional gauges find challenging to accommodate.
Without force-sensing technology, polishing and sanding applications cannot be developed. Knowing how much force to apply to an object is critical, as is accommodating concave and convex surface variations.
Flexibility Unleashed: The Seven-Joint Design
Robots must be as flexible and adaptable as humans to replace manual labor effectively. The human arm is an evolutionary marvel with seven points of articulation, and that is why adaptive robots commonly include seven degrees of freedom (DOF). When compared to a traditional collaborative robot’s six DOF, this extra dimension of movement provides enhanced flexibility and maneuverability in complex operational environments.
With each joint featuring its own torque sensor, the robot is provided precise control over every DOF, enhancing the overall accuracy of its operations. This precision is vital, especially in applications such as sanding.
Force control performance can also be further improved through optimizing joint configurations. With the help of the extra DOF, the robot can use the most efficient ‘joint’ configuration to achieve the best possible force control response and accuracy.
To illustrate the importance of articulation and sensitivity, imagine hand-sanding a piece of wood; the coordinated movements of your wrist, elbow, and shoulder, in conjunction with your tactile feedback, are fundamental to the sanding process. If you attempted to sand with thick gloves on or with an immobilized elbow, the task would become incredibly difficult and time-consuming.
In essence, by including a seventh degree of freedom into material abrasion tasks, the process becomes not only easier to conform to but also kinematically more efficient, with an increased level of precision.
Revolutionizing Precision with Direct Force Control
Central to the material abrasion process is the implementation of direct force control. This method instantly transforms force commands into joint torque commands, yielding much swifter response times to force changes. This method replaces the indirect force control often used by collaborative robots, where force is converted into joint velocity commands and subsequently into joint torque or current commands.
By skipping these intermediate steps, an adaptive robot can significantly diminish stiffness in the force direction, thereby greatly enhancing force control accuracy. This improvement is pivotal in fine sanding and polishing tasks, where maintaining meticulous force control is imperative for achieving a superior surface finish.
With direct force control, there is no need to install additional passive or active compliance devices between the robot’s flange and the sanders/grinders. This makes the entire sanding solution lighter, more reliable, more compact, and cost-efficient.
The Advantage of Omnidirectional Compliance
Omnidirectional compliance equips adaptive robots with the ability to control forces in all directions within Cartesian space. This represents an enhancement over traditional solutions that could only manage force in axial or radial directions.
Traditional robotic solutions are limited in this regard due to their reliance on compliance devices. Their inherent design limitations confine them to producing linear or rotational movements along or around specific axes. Although this traditional technology can still be used for basic abrasive tasks, multi-directional force control is often necessary in real-world manufacturing.
Omnidirectional compliance is vital for intricate material abrasion tasks requiring simultaneous force control in multiple directions. If we imagine a robot sanding an object with complex curves and uneven surfaces, there must be more than merely axial or radial force control. Complex shapes require dexterity in force control across all directions in three-dimensional Cartesian space.
Robots equipped with this omnidirectional compliance can precisely define force adaptivity in any Tool Center Point (TCP) frame. This capability allows for dynamic adjustment of the force exerted, relative to the robot’s end-effector, enhancing versatility in complex tasks.
Omnidirectional compliance is also crucial, especially with equipment like belt sanders where the robot holds the workpiece to it. To maintain continuous contact between the workpiece and belt sander, the robot must constantly shift its direction of force during the abrasive process. To accomplish this, an external TCP can be set with respect to the sander, resulting in consistent compliance direction, even as the robot’s pose changes during operation.
Omnidirectional compliance is a powerful tool that broadens the range of material abrasion tasks that a robot can undertake. The integration of advanced force control with omnidirectional compliance not only enhances flexibility but also streamlines the calibration and fine-tuning process, reducing the time and effort taken during deployment and finetuning.
Contact Angle and Contour Following
Programmable contact angles let operators define the average force exerted on a surface directly, an improvement over conventional methods where the contact angle affects the force. This has significant implications for industrial grinding tasks, enabling operators to vary contact angles along the grinding path without altering force control settings, thus maintaining consistent pressure.
Contour following, another advancement leveraging omnidirectional compliance, stands in contrast to traditional systems that struggle with maintaining constant force against irregular shapes. Contour tracking permits real-time automatic adjustments to force direction, ensuring consistent exertion, regardless of surface contours or robot movements.
These dual features increase the output quality of the material abrasion task and reduce the time required for trajectory tuning. Simply put, contact angle and contour following can reduce deployment time from hours to minutes. This facilitates the deployment process and minimizes the need for constant adjustments, enabling workpieces to be completed faster and to a higher standard than previously possible.
Enhanced Durability with Vibration Reduction
Vibration reduction is essential for material abrasion tasks. Excess vibrations can damage workpieces and significantly shorten the operational lifespan of mechanical systems, especially in high-vibration applications like grinding.
Flexiv tackles this issue by reducing vibrations by approximately 25-50 percent through joint torque control. This not only extends the operational lifespan of the equipment used by the robot but also enhances the overall workpiece quality by eliminating the ’swirls and whirls’ on surfaces that vibration can cause during the material removal process.
Future Outlook
The field of robotics is rapidly advancing, and the recent developments in adaptive robotics have enabled groundbreaking solutions to be created which were simply impossible with traditional collaborative robotic technology.
Robotic material abrasion still presents formidable challenges; however, direct force control, omnidirectional compliance, and vibration reduction make effective solutions feasible and practical.
Being able to sense with more precision than previously possible opens up a new range of automation possibilities. When we couple this with platforms like the NOEMA artificial intelligence system, there are practically no limits to what processes can be automated.
Material abrasion automation is evolving in tandem with advancements in hardware and intelligent software solutions, marking a shift from the traditional labor-intensive approaches and execution methods which were common only a few years ago.
Looking forward to the future, automated material abrasion could become as commonplace as automated screw fastening or pick and place applications.
This article was written by Ran Xu, Robotics Engineering Manager, Flexiv Robotics (Santa Clara, CA). For more information, visit here .
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This article first appeared in the April, 2024 issue of Motion Design Magazine.
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