- Folder Contents
- Introduction
- Object Assembly
- Fabrication
- How to Place Polhemus Sensors and Retro-Reflective Markers in Objects
- IMU Object Setup
In this repository you can find:
- CAD and STL files of the rigid and soft manipulation objects.
- Code examples for processing data.
- In-hand manipulation example data with the T42 and NDX-A* robot hands.
The human hand is Nature's most versatile and dexterous end-effector and it has been a source of inspiration for roboticists for over 50 years. Recently, significant industrial and research effort has been put into the development of dexterous robot hands and grippers. Such end-effectors offer robust grasping and dexterous, in-hand manipulation capabilities that increase the efficiency, precision, and adaptability of the overall robotic platform. This work focuses on the development of modular, sensorized objects that can facilitate benchmarking of the dexterity and performance of hands and grippers. The proposed objects aim to offer; a minimal, sufficiently diverse solution, efficient pose tracking, and accessibility. The object manufacturing instructions, 3D models, and assembly information are made publicly available through the creation of a corresponding repository.
Each object of the sensorized object set consists of 5 to 13 parts:
- a plastic screw (which holds the object together)
- two object halves (these halves can be objects of any size and surface stiffness)
- two removable urethane marker mounts
- eight removable object weights (optional components)
STL files are included in the CAD folder.
If the plastic screw does not screw into the object, a M8 tap and die can be used to fix any tolerancing errors introdruced by the 3D printing proccess.
NOTE: The plastic screws should not be overtightened or they will break (using SLA or SLS printing proccesses can increase the strength of the screw).
Note: Before molding the mold should be sprayed with mold release and ensure not to spray objects as this may prevent the objects soft skin from sticking correctly to the soft object halves.
- Read the urethane/ silicone instructions to determine mix ratio and work time
- Work time will determine how quickly you will need to degas and inject the material into the mold.
- Pour appropriate resin and hardener portions as instructed by the suppliers mix ratio.
- Mix together thoroughly.
- Place mixture into vacuum chamber to degas.
- Pour or inject urethane/ silicone mixture into mold.
Instructional videos for molding the markers can be found below. When molding the markers using a softer urethane or silicon (e.g Smooth On Vytaflex 30) will make insertion and removal of the markers into and out of the object halves significantly easier.
Before molding the objects a narrow nozzle syringe needs to be prepared in order for the chosen urethane or silicone to reach the small narrow spaces in the mold without air bubbles.
Materials needed to prepare long nozzle syringe:
- Syringe
- Heat shrink
- Pliers
- Super glue
The materials can be seen depicted below with an accompanying video demonstrating how to fabricate one.
Assembly of the molds can be seen below with exploded views of the mold and assembly videos.
Cube and radially split cylinder molds will require aluminum tape to the mold seams to prevent potential leaking.
Components required for molds:
- For object halves with internal threads
- 1 x M8 screw of 20mm length
- For object halves without threads
- 1x M8 screw of 35mm length
- 1 x M8 nut
Note: The walls of the mold should be parallel to the soft object core as shown in the image below to prevent misalignment.
- Radially Split Cylinder
- Axially Split Cylinder
For Polhemus markers only the first 2 steps of the video need to be followed. The last step is only relevant if you require optical markers.
The demolding proccess of cubes and radially split cylinders are the same, as well as for the spheres and axially split cylinders.
For retro-reflective markers only the first 9 seconds of the below video need to be watched.
- Assemble object.
- Insert retro-reflective markers into marker cavities.
- Insert micro sensor through the hole of the Polhemus urethane marker.
- Insert the micro sensor into the 2mm hole at the base of the screw. Note: If the sensor can't fit into hole a 2mm drill bit will need to be used to correct the dimensions of the hole.
- Place blu tack around the cable at the base of the screw. This will prevent the sensor from falling out, but will still allow it to be pulled out if a sigincant tug force on the cable is experienced.
- Once the screw and the sensor are in place, the Polhemus urethane marker can then be inserted into the corresponding object half.
The Object will contain:
- 1x Arduino Nano IOT (consists of onboard IMU and bluetooth comunication)
- 1x Powerboost 500 (a boost converter board for 5V output)
- 1x 180mah lipo battery
Denpending on the chosen object the length of the soldered wires will vary. For small objects only the rigid cube and cylinder shapes are supported. The imu implementation is suppoerted accross all medium and large sized objects support.
The small and medium ranges, plus the large sphere have the electronics installed in one of the 2 object halves. For the large objects (cube and cylinder) the ellectronics are supported in 1 of the 8 object weights. The relevant CAD files can be found above under the CAD Folder.