This section introduces a novel conveyor belt mechanism integrated within a custom tendon-driven robot with a sub-centimeter diameter. It details the mechanism design and manufacturing, robot design, system assembly for actuation, and a novel use for inter-robot coupling.
Mechanism Design
The conveyor belt mechanism runs the length of a tendon-driven continuum robot and is displacement-controlled by a pair of motors at the base. Two notched channel profiles are cut into each robot spacer disk, offset from the centerline. One channel cutout is open toward the robot’s outer circumference, while the other is enclosed within it. A conveyor belt runs up one channel toward the robot’s distal end, around a bearing pulley at the tip, and back down the other channel. The robot design contains three pairs of channels, radially offset by 120 degrees, to support three conveyor belts.
Inter-Robot Coupling
Two robots, each with a magnetic conveyor belt of opposing polarity, can couple through magnetic attraction to form a multi-robot system. Two adjacent robots evert their conveyor belts at the same rate, exposing magnetic coupling points. As the magnets couple and slide down the robots, the process creates a “zippering” effect.
Methodology
The experiments characterize the conveyor belt mechanism and its application to inter-robot coupling for variable stiffness. First, the actuation requirements of the conveyor belt within a single robot are characterized. Then, a case study of tangential inter-robot coupling investigates stiffness gains from coupling and how stiffness changes with the quantity and location of coupling points.
For coupled configurations, measurements are collected from one robot end effector to represent the effective stiffness gains of the coupled system at that point. Characterizing the individual stiffening contributions from each robot in the system remains ongoing work.
Stiffness Characterization: Inter-Robot Coupling
Two robot coupling configurations are investigated as feasible forms of robot coupling. One mode changes the position of one robot and the coupling points relative to the robot being measured. The other changes only the position of the coupling points, independently of both robots.
The investigation quantifies how the effective stiffness of the coupled multi-robot system differs from that of a single uncoupled robot, and how it changes with the quantity and location of coupling points.
System Characterization
The results demonstrate the feasibility of integrating a conveyor belt mechanism into a sub-centimeter tendon-driven robot, with reasonable actuation forces and consequent robot tip displacement during actuation.
Belt actuation produces tip displacement of under 6% of robot length across the robot shapes tested. Ongoing work is characterizing this effect across a denser range of bending angles and with motorized belt actuation, which is expected to further reduce tip displacement when the tendon compensation step is applied. Future work could integrate a model-based compensation controller to reduce tip displacement further.
Stiffness Characterization
With the first coupling mode, a predictable trend in tip displacement was observed: displacement generally decreased with more coupling points or with coupling points closer to the tip. This suggests that the mode could be used to actively and continuously adjust robot coupling configuration during a task to achieve desired stiffness changes, eliminating the need to predetermine coupling points.
With the second coupling mode, no significant trend was observed between tip displacement and coupling point reconfiguration, either in quantity or location. This suggests that the mode could adjust the effective lengths of both robots’ free ends to meet changing end-effector dexterity requirements without significantly altering system stiffness. The reachable workspace of the coupled system remains under investigation.
The beam bending model underestimates true tip deflection because it assumes that the robot base is fixed at the most distal coupling point and does not capture compliance in the proximal robot body. Future work will place markers at each robot tip, coupling point, and base to isolate and model the stiffness contribution from each section directly.
The preliminary results reflect a single coupled robot configuration. The observed trends are expected to generalize to other tangentially coupled configurations, with variations depending on robot shape and relative stiffness contributions. Future work will investigate the effects of robot shape, non-planar coupling configurations, and integration of the belt into longer multi-segment robots.
Conclusion
The conveyor belt mechanism enables functional elements to be actively repositioned along a continuum robot body. Magnetic inter-robot coupling demonstrates one novel application of active repositioning for stiffness modulation. This contribution aims to inspire further development of active onboard reconfigurability as a means of enhancing continuum robot adaptability to changing task requirements.
Frequently Asked Questions
How does the conveyor belt move along the continuum robot? A belt runs up one channel, around a bearing pulley at the robot tip, and back down another channel. A pair of motors at the base controls its displacement.
How does the mechanism couple two robots? The robots use magnetic conveyor belts with opposing polarities. Their belts expose coupling points that attract and slide together in a zipper-like process.
What happened to tip displacement during belt actuation? Across the robot shapes tested, belt actuation produced tip displacement of under 6% of robot length.
How did coupling configuration affect stiffness? In the first coupling mode, tip displacement generally decreased with more coupling points or points closer to the tip. In the second mode, no significant trend was observed with changes in coupling-point quantity or location.