Dynamic Gripper Assembly
A critical engineering challenge we faced at Contoro Robotics was the inability of our gripper to pick up boxes exceeding a certain depth and weight
To remedy this problem, the Unloader team prototyped multiple solutions, ultimately, deciding on a gripper with 2 faces that employs a hinge mechanism. I was in charge of the design of the fifirst iteration of this assembly
Concept
The idea to utilize two faces stemmed from the problem that our previous single face gripper could not handle certain loads due to the moment created, the weight was not supported evenly, causing failure. In addition, some boxes were too long for the gripper to pick up.
This design was based on the idea of one static face that would be stationary, with another dynamic gripper face that uses a hinged joint to swing down, allowing vacuum suction from a perpindicular plane.
Constraints and Challenges
Transforming the current gripper to this new version had some challenges and restrictions built in. The functionality of the gripper was a key aspect that needed to be maintained. Making sure that all the vacuum chamber, piping, and hinge mechanics were placed correctly with assembly and space constraints in mind were challenging and took some custom pieces to make it all fit seamlessly.
In addition, the height of the entire assembly was restrained due to interference with other parts of he KUKA arm, changing the geometry of the housing and the support of the solenoid.
Lastly, the geometry and design for the hinge mechanism took multiple reiterations and tweaking to ensure the dynamic face would move how we wanted without interference.
Hinge Mechanism
The cornerstone of this design is the mechanism that drives the movement of the dynamic face. This assembly is a four bar linkage driven by a powerful servo motor. Each linkage was designed for a specific length and geometric fitting from end to end and these pieces fit together using press fit wheel bearings. The geometry of these linkages utilized a lot of robot mechanism design, and took some trial and error to ensure the piece worked in the assembly.
The entire mechanism is connected to the outer cover through a static mount that has multiple mounting points for versatility in height. Furthermore, the last link, a shelf, was made to mount to the top of the dynamic gripper face.
This mechanism was designed with the intent of only on side being driven by a motor, and the other side being mounted through a two bar linkage that simply rotates on a bearing. These designs and parts were also tested and prototyped through 3D printed pieces.
Assembly Design
As mentioned, to ensure all the parts needed to maintain function to the gripper were integrated and mounted securely, some changes and shifting needed to be done. The static face has a pipe fitting for the vacuum, a solenoid, the hinge mechanism motor and mount, This greatly restricts the space given.
To mediate this I altered the original design of the gripper plate and chamber, pushing all the mounting holes to the outside edge. I then redesigned the chamber that redirects the solenoid into the static gripper, increasing the height, moving the solenoid up and allowing space for the motor underneath. Lastly, I researched and tested different flexible pipes to fit the solenoid to the dynamic plate and maintain connection through movement. There was also space in between the plates for our motion tracking cameras.
The last piece was the outer cover. This piece is an intricate, thick aluminum sheet metal piece that houses the entire assembly. The mounting patterns were placed carefully to ensure the mechanisms did not interfere with any other pieces, and multiple mounting options were made for various geometries.
FEA and Assembly
The last step was to run FEA on the most dynamic piece in the load path to check for deformation. Noticing some critical points of concern, I added more fillets and thicker metal to combat this.
Although I was not at the company for the assembly, I worked with vendors to make some minor tweaks for machinability and sent these parts to get made. This new gripper design was assembled and successfully used, with the one drawback being a singularity in the mechanism
