In a recent article published in the journal Scientific Reports, researchers presented an innovative gripper known as the cable loop gripper (CLG). This gripper is designed to handle objects of various shapes and sizes efficiently, requiring very little clearance. It operates using a flexible cable loop mechanism that can adjust its diameter to securely encompass target objects. The CLG shows promising applications in robotic automation, particularly in the execution of chemistry experiments.
Cable loop gripper prototype grasping various Chemistry glassware. Image Credit: https://www.nature.com/articles/s41598-024-59372-1
Background
Robotic automation is rapidly becoming indispensable in modern chemistry laboratories, enhancing both the reliability and throughput of experiments. This advancement facilitates the generation of extensive data, which is crucial for improving artificial intelligence models that navigate chemical spaces and strategize syntheses.
However, one of the main challenges of implementing robotic systems in chemistry is the manipulation of laboratory supplies and equipment, which often vary in size, shape, and orientation. Therefore, there is a need for versatile and adaptable grippers that can handle different types of objects without requiring extensive customization or reconfiguration.
Many existing grippers utilized in chemistry automation follow the principles of industrial automation, employing parallel jaw grippers equipped with custom-designed fingers and fixtures for handling supplies. However, this conventional approach is costly, inflexible, and challenging. For example, accommodating different types of vessels frequently requires redesigning the gripper components, which adds both complexity and delays to the process. Additionally, parallel jaw grippers generally require a significant amount of space between objects, which limits their efficiency and versatility across various applications.
About the Research
In this paper, the authors introduce the CLG, which leverages the flexibility of a cable to completely encompass the target object. In this approach, the cable is guided through a rigid finger, enabling the loop to encircle objects with minimal clearance and offer support upon completion of the grip. This gripper design minimizes the control effort needed to execute grasping tasks, as it simply adjusts the size of the cable loop based on the object's diameter and the required grasping force.
The study developed and assembled a prototype of a CLG specifically designed for tasks in chemistry automation. This prototype demonstrated exceptionally high grasp reliability, with a failure rate of less than or equal to 1 %.
The prototype consists of several critical components: a 1.75 mm diameter thermoplastic polyurethane (TPU) filament used as the cable, a 15 mm wide finger that includes a channel to guide the cable and is equipped with a capacitive force sensor, and a control box. The control box houses a geared direct current (DC) motor, a rotary encoder, a camera, a servomotor control board, and a Raspberry Pi single-board computer. This setup enables the prototype to be integrated with a robotic arm for performing pick-and-place operations involving chemistry glassware.
The researchers also developed a specialized software package to manage the operations of the gripper, utilizing the Robot Operating System (ROS) middleware framework. This package includes a vision module designed to gather data about the cable and the target object through a camera affixed to the gripper. Importantly, the vision module delivers insights into the relative distances between the center of the loop and the object's center as seen on the image plane. This feature significantly enhances the accuracy of vertically positioning the loop over the top of the object.
Furthermore, the software uses a force sensor and a rotary encoder to regulate both the loop size and gripping strength through two distinct proportional-integral (PI) control loops. This comprehensive software integration enhances the gripper's functionality by enabling real-time adjustments based on feedback from various sensors, thereby optimizing performance and ensuring reliable grasping of objects in diverse scenarios.
Research Findings
During testing in simulated chemistry lab environments, the prototype demonstrated its capability to handle vials of varying diameters and weights. With a failure rate of 0.8 %, all failures occurred during grasping, with no instances of vial loss during movement. Each manipulation task was completed in approximately 8 seconds, a speed comparable to human performance.
Moreover, the prototype exhibited robust performance despite variations in the target's position, tolerating deviations of up to ±15 mm from the expected target position. The researchers highlighted the device's commendable compliance and error recovery capabilities. Throughout the pickup and deposition phases, the cable loop could deform and adapt, facilitating successful grasping and recovery from positional errors without dropping the vial.
These results underscored the effectiveness of the prototype in simulated lab environments, showcasing its reliability, speed, and adaptability to variations in target positions. Such performance attributes position the gripper as a promising tool for automation tasks in chemistry labs, offering potential improvements in efficiency and precision compared to manual operations.
Conclusion
In summary, the novel gripper demonstrated its efficacy in manipulating test vials within chemistry lab settings, irrespective of size or storage density in trays. Its adaptability extends to other environments requiring precise grasping of prismatic objects, such as agricultural or logistics automation.
The researchers also highlighted the potential integration of CLG into a finger of a parallel jaw gripper, enhancing versatility and enabling manipulation of large trays or objects with intricate shapes. They recommended further improving the design and control of the mechanism as well as testing it in more realistic scenarios and with different types of objects.
Journal Reference
Manes, L., Fichera, S., Fakhruldeen, H. et al. A soft cable loop based gripper for robotic automation of chemistry. Sci Rep 14, 8899 (2024). https://doi.org/10.1038/s41598-024-59372-1, https://www.nature.com/articles/s41598-024-59372-1
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