myCNC Online Documentation

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===== MyCNC closed loop configuration =====

A proportional–integral–derivative controller (PID controller) is a control loop feedback mechanism widely used in industrial control systems and a variety of other applications requiring continuously modulated control. A PID controller continuously calculates an error value E(t) as the difference between the desired setpoint position (POS) and a real position measured by [[mycnc:rotary_encoder_connection_and_setup|encoders]] (ENC) and applies a correction based on proportional, integral, and derivative terms (denoted P, I, and D respectively). 


PID controller formula implemented in myCNC is 

{{mycnc:closed-loop:closed-loop-pid-002.png}}

where

  * **Kp** is the proportional gain, a tuning parameter,
  * **Ki** is the integral gain, a tuning parameter,
  * **Kd** is the derivative gain, a tuning parameter,
  * **E(t)** = (POS − ENC) is the position error (difference between a job position real position measured by encoder),
  * **t** is the time (the present).

Digital-Analogue Converter (DAC) output voltage is the sum of the **PID** and a **DAC offset** volage

{{mycnc:closed-loop:closed-loop-pid-003.png}}


Enable/Disable PID control does not affect the DAC voltage offset.

If PID control is disabled for selected channel, output voltage is equal to DAC Offset
<code> U_out = U_offset </code>


==== PID controllers setup ====

To setup Closed-loop analogue PID


  * Goto "Encoders" configuration widget. Setup Encoder resolution for each channel you going to use  \\ {{mycnc:closed-loop:mycnc-closed-loop-001.png}}
  * Set Multiplication ratio to "2" and divider (/2^Div) ratio to "1" to get result ratio \\ **2/(2^1)=1** \\ {{mycnc:closed-loop:mycnc-closed-loop-002.png}} 

<code>Multiplicator and divider ratio needed for pulse-dir closed loop system 
to adjust encoder resolution (encoder lines-per-rotation) to motor driver 
pulse-dir resolution. 
For Analogue closed loop system this ratio should be "1"</code>

  * Adjust DAC offset ratio to get "0V" value on DAC output for each channel. Theoretical DAC value for 0V is the middle of 12bits range \\ 4096/2=**2048**. \\ A real value may vary +/-5%. \\ {{mycnc:closed-loop:mycnc-closed-loop-003.png}}
  * Fill Encoder channel for each PID (Motor#). \\ {{mycnc:closed-loop:mycnc-closed-loop-004.png}} 
  * To test selected channel, check "Enable" checkbox for the channel and enter initial value of "50" for Proportional P-ratio of PID controller. Press "Save" button to save the changes. We test PID#5 (motor channel #5) on the screenshot below. \\ {{mycnc:closed-loop:mycnc-closed-loop-005.png}} 
  * Click on "Servo-ON" button to reset & enable selected PID and turn ON "Servo-ON" signal. Servo-On procedure will ... 
    * Reset position error registers - **E(t)** and its Integral value.
    * Turn ON Servo-ON output to enable a servo driver
    * Turn ON all "Enabled" PID controllers (Checkboxes "Enable" are checked).
  * Select the channel for a scope widget to control and tune PID controller ratios. \\ {{mycnc:closed-loop:mycnc-closed-loop-006.png}} 
  * Check which Axis the PID controller attached to (Y axis for the screenshot below). \\ {{mycnc:closed-loop:mycnc-closed-loop-007.png}}
  * Jog buttons can be used to move the axis while testing and tuning the PID coefficients. \\ {{mycnc:closed-loop:mycnc-closed-loop-008.png}}
  * An analogue servo driver normally has a linear function of rotation speed depends on input voltage. A linear coefficient of this function depends on Servo driver and motor, gears, ball-screw etc. \\ PID **K** value represent this coefficient. \\ {{mycnc:closed-loop:mycnc-closed-loop-009.png}} \\ The value can be tuned manually. If rotate a motor shaft with speed more than 20 turns/sec, the controller calculates real Speed/Voltage coefficient and print it on the configuration widget. You can use this value as information to tune the PID **K** ratio. A button **<<** to the right of **PID K** input line can be used to copy the measured **K** ratio to **PID K**. \\ {{mycnc:closed-loop:mycnc-closed-loop-010.png}}

==== Servo ON handling ====

Depends on machine configuration you may want 
  * On-Screen buttons to turn ON/OFF your Servo drivers
  * Automatic turn ON Servo Drivers when CNC control loaded and ready to go

Both options can be implemented with myCNC control software.

There are few ways to Enable/Disable Servo PID loops in myCNC software

1. On-Screen button. To enable/disable Servo PID control button should have actions:
  
  action="servo-pid-on"  (enable pid) 
  action="servo-pid-off"  (disable pid)
  
For example

Buttons for Servo-ON and Servo-OFF
<code xml>
<gitem where="toolbar-servo" image="motor/motor-start" action="servo-pid-on" 
height="80" event="pressed-delay-1000" type="button"/>
<gitem where="toolbar-servo" image="motor/motor-stop" action="servo-pid-off" 
height="80" type="button"/>
</code>

Popup widget container for Servo Pid On/Off buttons
<code xml>
<quick-popup-layout>
<current>popup-servo</current>
<layout stretch="0" name="popup-servo" wa="80;160;right" orientation="vertical" skin="skin/metal-01">
    <widget stretch="1" spacing="0" name="toolbar-servo" orientation="vertical">myitems</widget>
</layout>
</quick-popup-layout>
</code>
Button to show containner with 2 buttons for servo-on/servo-off buttons and led to show current servo pid state
<code xml>
<gitem where="magic" position="960;0" width="80" height="80" image="motor/servo-driver" 
action="mypopup-toggle:popup-servo" xattr="56;4;20;20;led;green;round" 
address="outputs" number="47" type="xbutton" />
</code>

2. Using Global Variables API. Global variables 60000 and 60001 are mapped to turning On and Off Servo PID control.

  * Write "1" to register number **60000** will turn ON Motor closed-loop control PIDs
  * Write "1" to register number **60001** will turn OFF Motor closed-loop control PIDs
Reading this registers has no effect and return zero value. Read more about Servo ON/Servo OFF commands in this short manual: [[mycnc:servo_on_off|Servo ON/OFF]].

3. Automatic Servo ON/OFF. There are 2 handler procedures in Software PLC can be used to automatic PID ON/OFF.
  * **_HANDLER_INIT** - procedure executed once just after CNC control software loaded, connection with myCNC controller established and a complete configuration is sent to the controller.
  * **_HANDLER_EXIT** - procedure executed while myCNC control software shut down the process.

To handle automatic Servo ON/OFF writing to registers 60000, 60001 should be added to handler procedures.
Example is below

<code c __HANDLER_INIT.PLC>
main()
 {
  gvarset(60000,1);  //turn Servo PIDs On
  exit(99);
 };
</code>

<code c __HANDLER_EXIT.PLC>
main()
 {
  gvarset(60001,1);  //turn Servo PIDs Off
  exit(99);
 };
</code>


==== Analogue -10V/+10V outputs Test Mode ====

To test DAC outputs voltage range, rising/falling edges timings **DAC Test mode** is used.
DAC Test mode is activated if in **Hardware->Encoders** configuration dialog, **/(2^Div)** line for **Encoder#11** column set "99" value and press "Save" button.

{{mycnc:configuration:mycnc-configuration-dac-test-001.png}}

In DAC Test mode all DAC outputs generate **Zero >> MAX >> Zero >> MIN** sequence with frequency about 700Hz. Scope screen example is shown below.

{{mycnc:configuration:dac-test-01.png}}

  Value "99" should be used for DAC test mode ONLY! 
  For working mode any other value from "1" to "90" should be used in "/(2^Div)" line for "Encoder#11".





==== Analogue -10V..+10V/Incremental encoder closed-loop setup ====

  - Goto **Encoders** settings tab. 
    - Setup **Encoder resolution** for All Encoders used. 
    - Set Multiplication ratio **Mul** to "2" for all the Encoders.
    - Set Divider **/(2^Div)** to "1" for all the Encoders. Result Ratio willl be 2/(2^1)=1
    - Setup **Attached to motor** for all Encoders used.
  - 





==== Pulse-Dir/Incremental Encoder closed-loop setup ====

__Example:__ Let's use Motor output #2 (configured as axis X) and Encoder #1 to build closed-loop PID control.

  - Goto **Encoders** settings tab. If rotary encoder is used as a feedback - setup **Encoder resolution** for Encoder #1. For linear encoder set resolution **2500**. {{ mycnc:mycnc-configuration-encoders-001.png }}
  - Set **Mul** and **/(2^Div)** ratios to get result Encoder resolution equal to **Pulses-per-Unit** resolution. For example <code>Servo driver with 2500 pulses per revolution, 
Electronic gears "1" and ball screw 5mm are used. 
Linear encoder with 1um resolution used as a feedback.
=>((A)) Pulses per unit value is (2500*4)/5=2000 pulses per mm
Original Linear encoder resolution (1um) is 1000 pulses per mm, need to set 
multiplier to "4" and divider to "1" to get result ratio 
4/(2^1)=4/2=2 and 
=> result Encoder resolution is 1000* 4/(2^1)=2000 pulses per mm (which is equal to ((A))
</code>
  - Set **Attached to motor** to "#2"
  - Goto **Pulse-Dir Closed Loop** ang setup PID parameters for PID attached to Motor#2. {{ mycnc:mycnc-configuration-pulse-dir-closed-loop-001.png }} The most important parameters are 
    - PID proportional ratio Kp
    - PID integral ratio Ki
    - PID integral limit. An integral value will be limited by given value.
    - Encoder channel used as PID feedback