Step motor board

Hello to all,

 In the time from last post I have designed an realized the board for step motor driving.

Three step motors need to be driver by the controller in order to act as focuser. For step motor adapting an L298 bridge is chosen. From the market is possible found chip board with this component and radiator.

 Every board need 5 digital output for driving: Enable, IN1 (A phase +), IN2 (A phase -), IN3 (B phase +), IN4 (B phase -). It is not mandatory have the possibility to move all focus at the same time so phase signal can be common for all motor having maintaining one enable signal for each motor. In this way 3 enable signal plus 4 phase signal are needed.

No more digital output are available directly on raspberry board so the solution for increase its number is the use of a little board with the component PCF8574. It is a remote 8-Bit I/O Expander for I2C Bus

Because of step motor power signal can generate noise in the low power CPU signal is a good solution make outputs optoisolated.

 

This is the board schematic available also as external file 

This Board is designed so to be mounted up the I/O board. Mounting is shifted so to allow the plug and unplug of the connettors from I/O board and Raspberry and from I/O board and relè board

 

IO Baord

Raspberry has 17 GPIO pins able to be programmed as input or output so these can be used as digital I/Os. They manage segnals with few Volts with the same electric potential of Raspberry, it is not a good idea have a long wiring with these signals, the risk is for the incoming noise and electric spike, they could hung up the Raspberry CPU.

For this purpose an expansion board need to be developed where 8 digital signal 24Vcc are optoisolated and adapted to the Raspberry GPIOs voltage and 8 Raspberry digital outputs drives relès. Relés make outputs optoisolated so driven signals can go far way from Raspberry.

For each digital input a this circuit is implemented

For digital output we bought a board from the market suitable for interfacing with Raspberry. Unfortunately this board reveses the commands from Raspberry, this not acceptable because during the Raspberry boot up for a litte time all reles are on. For this reason on the board an 8 inverter ports (74LS240) is applied in order to have the correct driving condition.

An analog input is needed in order to get the current observatory temperature. We bought an I2C analog to digital converter ADS1015. This is able to get 4 single ended signal or 2 differential signal. We select the second option in order to connect one PT100 termoresistor, this assure e low noise signal. This is the only not optioisalted signal so ti can’t go much far away from controller. A trimmable resistance che adjust the current flowing in the PT100 so to have precise measure.

An I2C FRam memory is mounted allowing the controller to save information need to be retained when power down. It has 32Kbyte more than enough.

In the resource the full board schematic is available

Don't forget something

As Alex Osborn said: "ideas evaporate faster than water". I think is better fix all the steps and project decisions in a document so it is possible review them in a long time.

Now in the resource gadget on this page you can find a link to that document. Now it is incomplete but I want update it along this project so at the end it can be use for reproduce and fix it .

Motors are running !

We realized an application for test driver and motors on bench. As you can see wiring is rather confused... but is only temporary for test.

you can find here the Codesys application for this test:

http://www.osservatoriobassano.org/TCS2020/TestEthercatDriverRaspberry.zip

 

In order to reach this result driverd

need to be parametrized for the specific motor and application. This is dome using the Infranor software “Gem Drive Studio”. It can be downloaded from Infranor website.

Voltage level are left as default, external breaking resistor in not needed

We selected the motor model we have, all parameters are set automatically

Auto phasing was asked, this activated a procedure for sensor phasing.

Position loop is set for minimum following error this is the best for this application.

Autotuning procedure was asked, this activated a strong step movement for loop gain computing. This procedure will ‘be done again when motors will be mounted on the telescope with real mechanical charge.

These are computed control parameters from autotuning procedure

Position sensor parameters are left as default.

This assure the position accuracy 360/4096 = 0.087 °

All other parameters are left as default.

 

Raspeberry activation

Hello to all, 

work is in progress on the controller side.

We select Raspberry Pi 4 Model B as controller for the observatory. It is a medium performance controller and low prices, has a Linux operating system and is supported by Codesys. Many hardware peripherals are available on the market for Raspberry. CODESYS is the leading manufacturer-independent IEC 61131-3 automation software for engineering control systems. This provides us Ethercat fieldbus support, sophisticated motion libraries and communication libraries over IP. It is used for the brushless driving with DS402 profile.

Wifi connection is use for the communication with PC where Polypus is installed. Morover Raspberry has many GPIO lines useful for digital I/O connection and I2C line where many more complex devices can be manged.

For Raspberry OS installation the Raspberry Pi imager is used. It can be download from the official Raspberry website, it allows the OS selection. We used the raccomanded 

For Raspberry OS installation the Raspberry Pi imager is used. It can be download from the official Raspberry website, it allows the OS selection. We used the raccomanded

With this step the SD card is programmed ready to be inserted in the Raspberry board.

After that connecting Raspberry to: a video monitor, a USB keyboard and a USB mouse we have our own system running.

Other steps needs to be done in order to complete installation:

1. Insert pasword for pi user.
2. Connect wifi
3. Enable SSH protocol.

 

Now you have Raspberry with standard linux support. For application where the real time is important jiitter genarate by task context switch need to be reduced. For this porpose a stronger kernel have to be installed. It can be found at following address with the info for installation.

 https://www.raspberrypi.org/forums/viewtopic.php?t=250927 

On this Linux system we install the Codesys runtime for Raspberry. First step is the Codesys developing system (IDE) on a PC. Main purpose of this software is the application developping. It can be dowloaded for free with this link:

https://store.codesys.com/tag/product/list/tagId/38/

After download ad installation we have the environment running

For Raspberry runtime installation and programming an extra package need to be get from Codesys website from this address

 

https://store.codesys.com/codesys-control-for-raspberry-pi-sl.html

This package is not for free but without license it is possible use it in demo mode for 30 minutes after that it is automatically stopped. This is enough for developping and evaluation.

Package needs to be installed in the codesys with menu command: tools/Package manager.

After package installation with the command: tools/ Update Raspberry Pi we have this panel. Selecting Raspberry IP address, giving the password for pi user you set in the OS installation and pressing “Install” button you have codesys runtime on our own device.

Now Raspberry is ready to accept Codesys application.

In the next day we'll delevop a test application for motion movement ..

Brushless motors and servodrivers

A friend of mine, owner of a company that uses a lot of motors, was very kind and gave me two high performance bruschless motors. With this motors we intend to drive the right ascension and declination of the telescope.

The motors are equipped with a resolver that allows to control the motor position to less than a tenth of a degree. 

Then we purchased two Infranor servo drives capable of driving these motors through the Ethercat fieldbus with DS402 profile.

Now we need the controller for the initial tests.

Introduction

Hello everyone, the Bassano Bresciano observatory (code 565) has been fully automated and remote controlled for some time. It can work automatically all night without the presence of operators and can be remotely controlled. Now the growing needs require a rethinking of all parts of automation. We open this blog with the intention of publishing all the steps that we will perform in this modernization operation allowing anyone to access projects and software in the hope that they will be useful.