Pick and Place Machine
From ZB45 wiki
- 1 Mechanical Parts
- 2 Electronics designs
- 3 Software
- 4 Camera
NEMA17 1.8 degrees/step - 200 steps per turn
Z-motion and rotation are dependent. To move in z, run only the z motor. To rotate, run both the rotation and z motor at the same rate.
Approximate (micro)steps/mm for the two axes using belts:
- 96.87 steps per mm X (left/right)
- 98.28 steps per mm Y (forward/backward)
probably the true vales are the same. Backlash may cause inaccuracy.
Motor control: USB Joystick -> Raspberry Pi B+ -> Arduino Mega -> RAMPS board
One diode on our RAMPS board has been removed, so the board does NOT power the Arduino. This allows the RAMPS board to use a higher supply voltage, but the Arduino must be powered separately.
Microstepping settings: all jumpers present (under the Pololu boards) -> 32 micro steps / step. Our drivers are DRV8825.
The end stop part number is not visible on the end stop, only the manufacturer Omron.
Brown - Vcc, 12-24 V
Black - open collector output, pulled low when end stop is activated.
Blue - GND
Wiring: 10k pull-up to 5V on the output, to get the output between 0 and 5 V. Possibly: internal pull-up of the arduino is enough, then no external wiring needed!
RAMPS board: VCC in the end stop connector is 5V. Pinout: signal, gnd, Vcc, with signal towards edge of the board. End-stop cables: Red-Vcc, Black-GND, Green-signal.
The sensor seems to work with Vcc = 5V -> we can use the end stop connectors directly - except for the pin-out. The stops on the machine has the pinout gnd, signal, vcc. Female connector.
- Current state*: the current cables are 70 cm, which is too short. 2 of them are joined by pin-header pieces - temporarily. The X end-stop is wired with jumper wires to the socket on the machine. The firmware doesn't
support endstops yet.
12V. Brown lead -, blue lead +.
The suction pump can be wired between +12V and the 3rd screw connector from the left - D9 on the Arduino. 4th screw from the left is +12V. A red LED on the RAMPS board lights up when this output is active. At 12V, the pump draws 100 mA while running, 500 mA if stalled (inlet blocked). The pump is rated for 24V.
GitHub repository : pick_n_place
The arduino program controls the stepper motors using the AccelStepper library.
Installation of AccelStepper: download zip Arduino IDE: sketch->include library-> add .zip
The arduino receives commands over the serial link, and generates stepping pulses. The program contains configuration variables for the maximum acceleration (steps/sˆ2) and axis range (steps). The program will not step outside the defined range for any axis, or below 0.
The current commands are:
|S||Stop||Stop as soon as possible without loosing position.|
|W||Where||Reply with the current position, four integers.|
|V x,y,z,r||Velocity||Set the target velocity for each axis x,y,z,r are integer values for steps/second.|
|P||pick||turn on suction pump|
|p||place||turn off suction pump|
- integers can be negative
- if arguments are missing, they are assumed to be 0
The V command sets the target velocity. The motors accelerate to this velocity, with the maximum acceleration for each axis, which is defined in the arduino program.
Additional planned commands, not implemented:
|G x,y,z,r||Go||Go to the absolute position specified by x,y,z,r as fast as possible.|
|M x,y,z,r||Move||Move x,y,z,r steps relative to the current position as fast as possible.|
- vacuum pump and valve control
- set acceleration and axis ranges ?
Note: This is not Gcode. A move will not be along a straight line, since the axes can have different acceleration settings. The Accelstepper library supports straight-line movement for several motors, but only with a constant velocity - not with acceleration. These commands will be useful for bookmarking locations, e.g. above the component storage and above the target circuit board.
- on some platforms, it seems pygame will not process events unless a display is initialized
- on the raspberry, there were some permission issues. I had to run the script as root to access the joystick.
- no longer the case with the latest Raspbian
Raspberry Pi 3 setup
- Copy Raspbian image to SD card
- resize SD card in the raspberry config GUI, set keyboard layout (US)
- WiFi: add to /etc/wpa_supplicant/wpa_supplicant.conf
- aptitude update, upgrade,
- sudo aptitude install arduino emacs
- clone the repository
- make ssh public key, add to github as deployment key
- git clone email@example.com:fjansson/pick_n_place
- host program: pick_n_place/host/control-pygame.py
- Arduino IDE
- AccelStepper module - download and install with the IDE
- python modules
- menu->preferences->Raspberry Pi Config, enable camera
- set GPU memory to 128
We currently have the following two joysticks.
Logitech WingMan Extreme Digital
PC game port joystick. The old-school analog mode works, but only when the joystick is powered. The two stick axes, the hat switch, and two buttons work in the analog mode. In the github repository is a program for a Pro Micro board, to convert an analog game-port joystick to and USB joystick (pick_n_place/joystick/pro_micro_joystick/).
USB joystick. Will use this one for now, since it gives easy access to all buttons.
Button numbering (starting from 1, most buttons have their number printed on them):
- trigger - 1
- hat - 2 down, 3 up, 4 left, 5 right
- base 6 - 11 , clockwise from top left: 6,7 left side, 8,9 towards user, 10,11 right side
Camera cable options:
PiCamera python module
- rotation is in multiples of 90 degrees - same in raspi-vid etc
- can position and size the preview window - move it on top of a regular window to simulate real windowing?