Embedded Files
Mechanical Design
Mechanical Design
3D View of the Gripper
The grasping motions are enabled by the linear motors. The relationship between the coordinate of linear actuators and the angular velocity of finger bending in a four-bar linkage mechanism exhibits a nearly linear correlation.
The configuration of the gripper grants rotational movement to side fingers by servo motors, which enables the robotic hand to adjust its grips for different types of object.
Fig. 1 Kinematic diagram of the finger’s range of motion, with R1 and R2 denoting pivot radii, and ’y’ representing the linear actuator’s endpoint displacement. θ indicates the finger’s bend angle. And a graph of the actuator’s y-displacement against finger bend angle θ based on mathematical modeling
Fig. 1 Kinematic diagram of the finger’s range of motion, with R1 and R2 denoting pivot radii, and ’y’ representing the linear actuator’s endpoint displacement. θ indicates the finger’s bend angle. And a graph of the actuator’s y-displacement against finger bend angle θ based on mathematical modeling
Fig. 2 finite element analysis of Fin Ray inspired finger under 100N/m2
The displacement in x direction is the smallest if the pressure is applied on the tip of the finger. Making the forces more concentrated in the smaller area, potentially leading to greater local stress when gripping object at the tip. Additionally, when manipulating smaller objects, precise actions are required. By using only the tip of the finger, the contact areas will be minimized to avoid interfering with or damaging other parts of the object. In this way, the performance for dealing with smaller objects, can be improved by using only the tip of the finger.
On the other end of the finger, it is more suitable for grasping large and heavy objects since the displacement in x direction is intermediate. This means it can transfer force onto the object and also conform to the object's shape in a good degree. Moreover the surface area of the back end fingers are designed to be very rough, increasing its friction for grasp larger and heavier objects.
While for the middle part of the finger, the displacement in x direction is much larger. which means the shape of finger can better conform to the shape of the object. Thus the pressure will distributed more evenly across the object and making the grip much gentler.
Force analysis
In the maximum load analysis, simulation is carried out in ADAMS based on the principles of theoretical mechanics and multi-body dynamics. In the simulation, an object is positioned at the center of the robotic fingers to evaluate grasping capabilities. Cubes, cylinders, and round objects are used for simulation, as shown below
During the simulation with the cylinder, the maximum deformation observed in the gripper is 13.62 mm. In a similar test featuring the cube, the deformation is marginally less, measuring 12.89 mm. When the tip of a Fin-Ray structure is excessively pressed, it exhibits a pronounced outward deformation in the opposite direction. This effect is particularly noticeable with shapes vastly different from a round object such as a sphere. Given its continuous surface in all directions of the sphere, the Fin-Ray structure can grip more tightly without creating gaps or losing contact. This leads to a larger contact area between the object and the grippe, resulting in a significantly smaller deformation, measured at 7.6 mm.
This figure displays the gripper's maximum force over time. For the cube and cylinder, their maximum forces are around 25 N, while for the sphere, it is 12 N. This result closely aligns with the deformation observed. Additionally, since the contact area for a spherical object is generally larger than that of the cube and cylindrical ones, the maximum pressure under the same force for the sphere should also be much smaller.
Equivalent elastic strain (mm/mm)
Page updated
Google Sites
Report abuse