Print-N-Grip: A Disposable, Compliant, Scalable and One-Shot 3D-Printed Multi-Fingered Robotic Hand

TL;DR

The paper introduces the Print-N-Grip (PNG) hand, a low-cost, disposable, tendon-based underactuated gripper that is fully 3D-printed in one shot from TPU and mounted on a universal base for rapid replacement in contaminated or harsh environments. It presents a modular design with one-piece fingers, scalable configurations (PNG-2/3/4) controlled via a central pulley, and a mathematical finger model that maps tendon pull to joint angles for design optimization. Extensive experiments validate the finger model, demonstrate high-load grasping across scales, and show fast fabrication-to-operation times, confirming PNG's robustness, scalability, and practical utility in hazardous settings. The work highlights PNG's potential to reduce equipment downtime and maintenance costs in chemical, biological, and radiation-prone industries by enabling quick replacement of contaminated hands without discarding the base.

Abstract

Robotic hands are an important tool for replacing humans in handling toxic or radioactive materials. However, these are usually highly expensive, and in many cases, once they are contaminated, they cannot be re-used. Some solutions cope with this challenge by 3D printing parts of a tendon-based hand. However, fabrication requires additional assembly steps. Therefore, a novice user may have difficulties fabricating a hand upon contamination of the previous one. We propose the Print-N-Grip (PNG) hand which is a tendon-based underactuated mechanism able to adapt to the shape of objects. The hand is fabricated through one-shot 3D printing with no additional engineering effort, and can accommodate a number of fingers as desired by the practitioner. Due to its low cost, the PNG hand can easily be detached from a universal base for disposing upon contamination, and replaced by a newly printed one. In addition, the PNG hand is scalable such that one can effortlessly resize the computerized model and print. We present the design of the PNG hand along with experiments to show the capabilities and high durability of the hand.

Figures (26)

• Figure 1: Three variations of the Print-N-Grip (PNG) hand: (top left) two-finger, (top right) four-finger and (bottom) small scale two-finger grippers mounted on a universal base and grasping a hammer, rubber duck and a bio-hazard bag, respectively.
• Figure 2: (a) Front and side view of a PNG finger. Internal view of the proximal link is seen in the circle where the two bands are separated by a bulge. Due to its height, the bulge prevents from the contact pad to press onto the bands. (b) Different scales $\kappa$ of a PNG-2 hand. As convention, a hand with a finger length of 52 mm is defined as $\kappa=1$. Correspondingly, the smallest and largest hands shown and evaluated are with finger lengths of 25.6 mm ($\kappa=0.5$) and 89.7 mm ($\kappa=1.75$), respectively. (c) Examples of three- (PNG-3) and four- (PNG-4) finger hands. Both hands are one-shot 3D printed. (d) Universal base for mounting the printed hand. The 3D printed hand is fixed to the base by inserting the mounting pins into the conical grooves and closing with the tightening cap. A reduction sleeve is used for hands of small scale. (e) Fingernail on the distal link assists in picking-up small objects.
• Figure 3: (a) PNG-2 and (b) PNG-4 hands on the 3D printer bed after printing is completed.
• Figure 4: Demonstration of the differential in the PNG-2. In this case, (left) the right finger is manually constrained with a ball and the left finger compensates for the increase in tendon force $f_{in}$. (right) The ball is not centered in the resulted grasp.
• Figure 5: Illustration of a PNG finger with $m=3$ joints when (a) relaxed and (b) in flexion.