Wall-climbing robots capable of scaling vertical surfaces could help automate hazardous or labor intensive tasks such as window washing, inspection, maintenance, and construction. Active adhesion methods achieve higher payload capacities, but require power to maintain their grip. Passive adhesion devices such as suction cups are an attractive option for such robots because they do not require power to maintain their grip, but they are limited by their payload capacity. This work presents a novel high-payload wall-climbing robot that utilizes passive bistable suction cups to generate adhesion without needing to be pushed into the wall. The robot features a track-based system that automatically engages and disengages bistable suction cups to achieve locomotion on smooth surfaces. The robot is able to achieve vertical wall climbing on glass, wood, metal, and painted surfaces, sideways and upside-down climbing, and is able to tow a payload of 7.940 kg (with a payload-to-weight ratio of 2.25).
Figures & tables
Fig. 1: The proposed wall climbing robot uses bistable suction cups to adhere to a variety of surfaces. It has been shown capable of (a) climbing vertically on a glass window, (b) climbing vertically on a wooden door, (c) climbing vertically on a steel door while carrying a payload, (d) climbing vertically on a painted wall, (e) wiping a whiteboard while traversing sideways on it, and (f) translating on the underside of a lab bench.
Fig. 2: Bistable suction cup design requires work to be done on the system to change configurations. (a) Disengaged position where cup is “inverted”. (b) Engaged position where cup is in the standard position. The force required to flip from disengaged to engaged is greater than in the other direction.
Engaged Position
Disengaged Position
Height (mm)
36
22.1
Diameter (mm)
69
71.6
Interior Radius (mm)
23.2
Interior Diameter (mm)
60
Wall Thickness (mm)
4
Mass (g)
34
TABLE I: SPECIFICATIONS OF BISTABLE SUCTION CUP
Fig. 3: (a) Full Wall-Climbing Robot Design (b) Adhere mechanism to take suction cup from disengaged to engaged position and adhere to surface (c) Track deflector to force the tread towards the robot frame (d) Flip mechanism to flip the cup from the engaged to disengaged position. (e) Break seal mechanism to detach cup from wall. Cups rotate in clockwise direction, marked in red
Size (mm)
524 x 200 x 161
Mass (kg)
3.532
Climbing Speed (cm/s)
11.5
Nominal Voltage of DC Motor (V)
12
Nominal Current of DC Motor (A)
0.25
Nominal Torque of DC Motor (Nm)
24.51
TABLE II: SPECIFICATIONS OF ROBOT
Fig. 4: The forces required to engage and disengage the suction cup were measured (a) The flip ring pulls the cup down to flip from disengaged to engaged (b) The flip ring pushes the cup up from engaged to disengaged. The machine moves flip ring in red direction.
Fig. 5: The pull off forces at different application distances were tested on two types of suction cups. Bistable (purple) suction up on the left and standard clear PVC suction cup on the right (a) The Application Distance measures the distance between the surface and the top of the interior dome of the suction cup (b) 0mm Application Distance (full compression) (c) 17mm Application Distance (little to no compression)
Fig. 6: Maximum pull off force at various application distance averaged over 5 trials for bistable (pink) and standard (aqua) suction cups were measured. Beyond 6mm the forces for the standard PVC cup fall to zero because it no longer makes contact with the surface due to its shallower design.
Fig. 7: Maximum pull off force at various sandpaper grits averaged over 5 trials for bistable (pink) suction cup were measured.
Fig. 8: The sliding force on different surface roughness levels was tested on the bistable suction cup. (a) The side view of the cup adhered to the test setup. (b) The back view of the cup adhered to the sandpaper.
Fig. 9: Force required to begin sliding at various sandpaper grits and acrylic averaged over 5 trials for bistable (pink) suction cup were measured.
Fig. 10: Average fall-off time of the bistable suction cup with a 1kg hanging mass across different sandpaper grits and acrylic, based on three trials blue shows the cup in shear conditions, orange shows the cup in normal conditions.
Fig. 11: A wall-climbing experiment was done on a steel door, left shows the starting position and right shows the final position. The black cable attached to the top of the robot was a safety cable to prevent it from falling when detached from the door and does not have any tension or provide any structural support to the robot.
The authors are with the Space Robotics Lab. (SRL) in Department of Aerospace Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan.
School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore · School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan430074, China