Dual-loop feedback position control - Revision history

Tero K: /* How to build a dual-loop system */

2014-09-22T19:56:58Z

‎How to build a dual-loop system

Tero K at 19:17, 14 August 2014

2014-08-14T19:17:43Z

Tero K at 14:57, 14 August 2014

2014-08-14T14:57:31Z

Tero K at 14:47, 14 August 2014

2014-08-14T14:47:50Z

Tero K at 13:05, 14 August 2014

2014-08-14T13:05:24Z

Tero K: Created page with "Work in progress 800px 450px 450px File:Controller position with error...."

2014-08-14T10:25:40Z

Created page with "Work in progress 800px 450px 450px File:Controller position with error...."

New page

@@ Line 38: / Line 38: @@
 ==How to build a dual-loop system==
-The most common method to make a dual loop system is to connect servo motor with rotary encoder to a servo drive and tune it for velocity control mode. The linear encoder feedback should go to the [[controller]] that implements it's own position control and outputs a veloicty setpoint to the servo drive.
+The most common method to make a dual loop system is to connect servo motor with rotary encoder to a servo drive and tune it for velocity control mode. The linear encoder feedback should go to the [[controller]] that implements it's own position control and outputs a velocity setpoint to the servo drive.
 {{picturebox|System dualloop.png|800px}}

← Older revision		Revision as of 19:17, 14 August 2014
Line 40:		Line 40:
	The most common method to make a dual loop system is to connect servo motor with rotary encoder to a servo drive and tune it for velocity control mode. The linear encoder feedback should go to the [[controller]] that implements it's own position control and outputs a veloicty setpoint to the servo drive.		The most common method to make a dual loop system is to connect servo motor with rotary encoder to a servo drive and tune it for velocity control mode. The linear encoder feedback should go to the [[controller]] that implements it's own position control and outputs a veloicty setpoint to the servo drive.

		+	{{picturebox\|System dualloop.png\|800px}}
	Servo drive can be also set in position or torque mode but the simplest solution is to use velocity control mode in the inner loop.		Servo drive can be also set in position or torque mode but the simplest solution is to use velocity control mode in the inner loop.

@@ Line 1: / Line 1: @@
 In many linear motion cases it is preferred to use linear encoder mounted directly to the axis to provide accurate position readout and to use it as feedback signal for position controller. The benefit of that is the elimiation of error sources between rotary motor and linear motion. This page explains the implementation of such system.
-==Background==
+==Background: traditional signel-loop feedback==
 A typical closed loop controller resembles the diagram below.
@@ Line 19: / Line 19: @@
 {{picturebox|Servolinearaxis.png|600px}}
-==Linear encoder feedback==
+==Dual-loop system: linear encoder feedback==
 The drawback of above position control system is the position error caused by lead screw backlash, pitch error and flex. The problem is that the error is unknown because it is not being measured or controller:
@@ Line 34: / Line 34: @@
 {{picturebox|Controller dualloop.png|750px}}
 [[category:glossary]]
 [[category:technology]]

@@ Line 4: / Line 4: @@
 A typical closed loop controller resembles the diagram below.
-[[File:Controller general.png|350px]]
+{{picturebox|Controller general.png|350px}}
 The closed loop system is formed by an '''actuator''', '''feedback''' and '''substraction''' (sigma):
@@ Line 13: / Line 13: @@
 In a practical case, this type of closed loop may be used for servo motor position control just by choosing appropriate components:
-[[File:Controller position.png|350px]]
+{{picturebox|Controller position.png|350px}}
 This kind of controller could be used to produce linear motion with appropriate mechatronics assembly such as:
-[[File:Servolinearaxis.png|600px]]
+{{picturebox|Servolinearaxis.png|600px}}
 ==Linear encoder feedback==
 The drawback of above position control system is the position error caused by lead screw backlash, pitch error and flex. The problem is that the error is unknown because it is not being measured or controller:
-[[File:Controller position with error.png|500px]]
+{{picturebox|Controller position with error.png|500px}}
 ===Dual-loop system===
 To elimiate the error of mechanics, one can add a linear encoder to read out the actual position of the axis instead of using derived value from rotary encoder behind the lead screw:
-[[File:Servolinearaxis dualloop.png|600px]]
+{{picturebox|Servolinearaxis dualloop.png|600px}}
 However the problem there is that we have two separate position feedback signals: rotary and linear. One may think to replace rotary feedback with linear feedback in the original system. However, that will cause stability problems to the control loop due to backlash and flex of the mechanics. If motor is being controlled based on feedback signal with time delay (due to flex and backlash), it will easily render control loop unstable or leave user with very [[Servo stiffness|low stiffness]].
@@ Line 33: / Line 33: @@
 In order to achieve stiff position control it is necessary to control motor by it's local rotary encoder AND control axis position based on linear encoder. Such system can be achieved by a dual-loop feedback system:
-[[File:Controller dualloop.png|750px]]
+{{picturebox|Controller dualloop.png|750px}}
 [[category:glossary]]
 [[category:technology]]

@@ Line 1: / Line 1: @@
-Work in progress
+In many linear motion cases it is preferred to use linear encoder mounted directly to the axis to provide accurate position readout and to use it as feedback signal for position controller. The benefit of that is the elimiation of error sources between rotary motor and linear motion. This page explains the implementation of such system.
-[[File:Controller dualloop.png|800px]]
+==Background==
-[[File:Controller general.png|450px]]
+[[File:Controller general.png|350px]]
-[[File:Controller position.png|450px]]
+The closed loop system is formed by an '''actuator''', '''feedback''' and '''substraction''' (sigma):
-[[File:Controller position with error.png|600px]]
+[[File:Controller position.png|350px]]
-[[File:Servolinearaxis.png|700px]]
+This kind of controller could be used to produce linear motion with appropriate mechatronics assembly such as:
-[[File:Servolinearaxis dualloop.png|700px]]
+[[File:Servolinearaxis.png|600px]]