Halberd v2

airo-halberd

The Halberd coupling (paper), named after its characteristic PCB shape, is a replacement of the Robotiq I/O Coupling enhanced with a Nina B301 microcontroller, developed at IDLab-AIRO, Ghent University (Belgium), imec. It is particularly suited towards robotic manipulation augmented by tactile sensing in the fingertips: the tactile sensors can be read from the robot wrist, without the need for external power or data cables.

This repo contains KiCad board files and SolidWorks casing design files of the project. See below for a guide from ordering to usage.

Features

Our coupling features the safety circuit present on the original Robotiq I/O Coupling, augmented with a Nina B301 microcontroller unit (MCU), capable of communicating wirelessly over Bluetooth Low Energy (BLE) and Wi-Fi. Eight analog pins and 15 digital pins are exposed. An SPI, UART, and two I2C interfaces are supported by a subset of the digital pins. The board is Arduino compatible and programmable over a micro USB interface.

Ordering & Assembly

The PCB was designed for JLCPCB's JLC04161H-7628 impedance controlled board material, with 1 oz. outer copper weight, 0.5 oz. inner copper weight, and 1.6mm board thickness. The reason why this matters is the use of an external antenna: a short trace connects the antenna (ANT) pin of the Nina B301 to a u.FL connector. This trace must be matched at 50Ω. Using JLCPCB's impedance calculator, the width of the trace was determined to be 0.350mm for the given board specifications. If you are unable to order a board with these specifications, you may suffer from degraded antenna performance, though the effect is suspected to be small as the antenna trace is only 0.75mm long (compare this to a wavelength of 122.45mm at 2.45GHz). Note that the board width of 1.6mm is essential for the pogo pin connection to the gripper.

A bill of materials (BOM) is included in main folder of this repo, mostly automatically generated from KiCad for ordering at JLCPCB, supplemented with some mechanical parts. For the production files you can use to order assembly at JLCPCB, see KiCad > halberd_v2 > production. The cable connecting the coupling to the robot is hard to find: it's an M8 8-pole female 90° circular connector. Many manufacturers provide this, however, usually the pin aligment is along the cable direction, while the Robotiq cable has a 90° angle between the pin aligment divet and the cable direction. So far, I've only found amissiontech to be willing to produce small volumes of this specific connector. Structural parts can be 3D printed in standard PLA and are found in the SolidWorks/parts_to_print folder. The below graphic indicates how the different parts fit together.

Usage

Programming

To program the board, first install the airo-nrf52840-boards package in your Arduino IDE. Compile ("Verify") the standard Blink example (File > Examples > 01.Basics > Blink) for the Halberd (I/O Coupling) board. Find the Blink.ino.with_bootloader.hex file by marking compilation in File > Preferences > Show verbose output during and monitoring the console output after compilation. Flash the .hex onto the board using a JLink EDU Mini, which you can connect to the board via the provided 10-pin 1.27mm pitch header next to the Nina-B301. This will automatically flash the Arduino bootloader, and the green LED should start blinking. From this point on you can program the board straight from the Arduino IDE over a µUSB connection.

Debugging

If you are connected to a UR robot via an ethernet connection, the Arduino IDE might show the error Method name - "openPort(); Exception type - Port not found when you try to upload. To avoid this, disconnect the ethernet cable, restart the Arduino IDE, and upload the code. You can now reconnect the ethernet cable.

Mounting

The Halberd coupling is mounted to your robotic arm just like the Robotiq I/O Coupling would be, similarly your Robotiq gripper is bolted to the Halberd just like it would be to the Robotiq I/O Coupling. The Halberd has the same height as the Robotiq I/O Coupling, so there's no need to redefine the robot's tool centre point. Also, the risk of self-collisions is no greater than when using the Robotiq I/O Coupling.

Application notes

• When reading analog signals, it's best to not use D7-D13 for high-frequency switching (e.g. PWM): the digital noise could couple to the analog traces.
• SERVO0-SERVO3 (also named D0-D3) are level shifted to 5V. The level shifter is bidirectional, so these pins can be used as digital inputs as well. However, the level shifter has a 4k series resistor at it's 5V output, making the D0-D3 pins less suited to drive resistive loads as a digital output: the HIGH output voltage would be divided accross this series resistor and the actual load.