Development of extremity gripper

14. september 2022

As part of Work Package 5, Danish Technological Institute (DMRI) has designed, built and tested a prototype gripper with successful results.

The necessity of a limb gripper is twofold: (1) support the weight of the limb under the cutting procedure and (2) assist the cutting robot by moving the limb position to create the optimum cutting conditions. After the cutting is completed to move the limb to the display frame for veterinary inspection.

The design offset is the manual DTI-DMRI gripper that has been tested and validated on cold primals (shoulders and hams). The focus in the development of a robot End-of-arm-tool therefore includes:

  1. Reducing the unit weight.
  2. Improving clean-ability (hygienic design).
  3. Designing an attachment flange to the ABB robot arm.
  4. Degrees of freedom of the gripper for warm carcass grasping.
  5. Centre of interaction relative to robot arm, compromise to cutting trajectory.
  6. Object manipulation requirements, constrains to cutting trajectory.

Focus points 1 and 2 are left to the final revision of the gripper design.

The robotized gripper design has been tested at NMBU during support of a manual cutting procedure to illustrate the functionality and to identify drawbacks. The test showed that there should be more room for the cutting procedure, especially of the hind leg. One more major finding was that the claws should be slightly wider in aperture to fit the front leg better. However, it must be changed in respect of the grasping robustness of the ham.

Watch the gripper hanging a ham on a «Christmas tree». The sleek design leaves room for the hook of the Christmas tree to penetrate the ham (shank). Video: DMRI

In parallel with the development of the cutting trajectories, the attachment of the gripper to the robot tool flange was optimized and tested in the complete process of supporting the cutting robot and moving the separated primal to the inspection frame (see picture).

The final version of the gripper placing the shoulder primal at the inspection frame. The fixation claw has been developed by NMBU. Photo: NMBU

As the gripper must handle all primals, incl. the saddle (see picture below), a stress analysis for a 40 kg load showed a maximum displacement of the gripping claws of less than 0.4mm, sufficiently rigid to perform a saddle handling in a future meat factory cell.

The final version of the gripper handling the saddle of the carcass by grasping the hipbone structure. The natural features of this bone offer good grasping loci. Photo: NMBU