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Implementation of Position Control Servo DC Motor with PID Controller to Humanoid Robot Arm

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In this paper implementation of position control servo DC motor with PID controller to humanoid robot arm is discussed. The objectives are development and analyze the movement of humanoid robotic arms before implementation to show the system response and get the least errors. Humanoid robot arms are mechanically controlled devices designed for emulated the movement of a human arm. The mathematical equations of servo DC motor are simulated and connected to PID controller using the MATLAB program. The PID controller is a closed loop feedback mechanism system. It calculates an error value from the difference measured process variable and desired value, and give pulse-width modulation (PWM) signal to send it to motor by microcontroller. As a result, the system response is getting without error and less overshoot. And besides, the disturbance is added to process (angle) and found that the system is returning stable after the disturbance is removed. With practical experience, the system achieved the same response and efficiency. Under this control, every joint of the arm could be moved by adjusting the angles of the motor. The different activities could be applied using the humanoid robot arm safely, because it’s stable system.
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5th IUGRC International Undergraduate Research Conference,
Military Technical College, Cairo, Egypt, Aug 9th Aug 12st, 2021.
Implementation of Position Control Servo DC Motor
with PID Controller to Humanoid Robot Arm
Nada Mohamed Zakaria.
October 6 University, Egypt,nm035186@gmail.com
Supervisor: Abdelrady Okasha Elnady, Associate Professor
Head of Mechatronics Department Faculty of Engineering,October 6th University, Egypt, rady_nady@yahoo.com
AbstractIn this paper implementation of position control servo DC
motor with PID controller to humanoid robot arm is discussed. The
objectives are development and analyze the movement of humanoid
robotic arms before implementation to show the system response
and get the least errors. Humanoid robot arms are mechanically
controlled devices designed for emulated the movement of a human
arm. The mathematical equations of servo DC motor are simulated
and connected to PID controller using the MATLAB program. The
PID controller is a closed loop feedback mechanism system. It
calculates an error value from the difference measured process
variable and desired value, and give pulse-width modulation
(PWM) signal to send it to motor by microcontroller. As a result,
the system response is getting without error and less overshoot. And
besides, the disturbance is added to process (angle) and found that
the system is returning stable after the disturbance is removed. With
practical experience, the system achieved the same response and
efficiency. Under this control, every joint of the arm could be
moved by adjusting the angles of the motor. The different activities
could be applied using the humanoid robot arm safely, because its
stable system.
Keywords: Humanoid robot arm, Servo DC Motor, PID
controller, MATLABSimulink.
I. INTRODUCTION
Humanoid robots are being used in the inspection,
maintenance and disaster response at power plants to relieve
human workers of laborious and dangerous tasks. They are
being developed to perform human tasks like personal
assistance, through which they should be able to assist the sick
and elderly. Simply speaking, the control electronics adjust
shaft position by controlling the DCservo motor.The position
data to the control should be sent in the form of PWM signal
through the Signal pin of servo motor. A Servo DC motor
alongside servomechanism (closed-loop control system) goes
about as a servo motor which is essentially utilized as a
mechanical transducer in the computerization business. A
servo framework is a shut circle framework where the
criticism signal (position, speed, and so on) drives the motor.
The motors are coupled to a yield shaft (load) through a stuff
train for power coordinating.
The main aim of this paper is to analyze the servo motor and
show cases hypothesis of dynamic DC motor about the
boundaries for (, , , , ) [1].Then speaks to
mathematical equations (close loop) for dynamic DC motor
without and with PID controller.
In this paper Position control of a 3rd ordered plant (Servo
motor) using Conventional PID [2],[3]. Simulation for
recreation and results for some cases, examines utilizing
MTLAB program. And besides, adding the disturbance to
process (angle) and finding that the system is returning stable
after the disturbance is removed. [4].
Practical experience, by connecting a real control system to a
PID controller with adjusting the angles of the motor, every
joint of the arm could be moved. It could be taught the
humanoid robot arm to perform those tasks by imitation and
learning it once [5].
II. METHODOLOGY
The control of adaptive robotic mechanical systems can
be approached using the general proposed formulation. This
methodology is based on the use of the basic principles of
control concepts. To build real control system: The
methodology can be divided into five main steps.
Step 1: Determine the system requirements. Position control of
DC servo motor to imitate the human arm by adjusting the
selected angle.
Step 2: Understanding servo motor control. The position data
to the control should be sent in the form of PWM signal
through the Signal pin of servo motor.
Step 3: Choose benefit of control and tune it.
Step 4: Controller simulation. PID controller is used to
improve the dynamic performance and also reduce the
steady state error of the systems.
Step 5: Controller implementation. Apply it to the DC-servo
motor to optimize and test if it is practically stable.
III. SYSTEM MODELLING
In this DC servo motor can be considered as a linear SISO
system having a 3rd order transfer function. Armature control
is a closed loop system, while field control is an open loop
system. Closed loop systems are often the preferred choice for
operators and business leaders who are looking for stability
and the convenience of a 108 automated process. Armature
5th IUGRC International Undergraduate Research Conference,
Military Technical College, Cairo, Egypt, Aug 9th Aug 12st, 2021 2
controlled motors offer nearly unmatched accuracy and
control, along with a wide speed variation range.
Advantages of armature-controlled DC motors include:
• Constant field current and torque: With the armature control
method, the field current and torque levels remain constant
throughout the application. Regardless of the speed of the
motor, you can rely on these factors.
• Fast and simple speed variation: Armature controlled DC
motors are known for their exceptional speed control, which
allows operators to vary the speed as necessary in both
directions.
The relation between shaft position and armature voltage is
derived from the physical laws [1]. Schematic graph of DC-
servo motor is shown in Fig.1.
Fig.1: Schematic of DC-servo motor.
The air gap flux is given by:
 (1)
Torque is proportional to product of Flux and Armature
current
    (2)
   (3)
The motor torque when the constant flux established in the
field coil is given by:
   (4)
Back EMF of the motor is given by:
(5)
So, differential equation for armature circuit servo motor
controlled by armature voltage:

    (6)
Armature current produced torque applied to the inertia and
friction:
    (7)
By apply Laplace transform:
     (8)
Where: Input voltage, Output .
So, transfer function
T.F = 
=
 (9)
TABLE I: PARAMETER VALUES [6]
Parameter
Label
Value
Armature Resistance
1 Ω
Armature inductance
0.5 H
J
Motor Moment of
Inertia
0.0093
kg/
B
Motor Viscosity
0.008 N.m. s

Motor EMF to speed
proportional constant
0.01
v/rad/sec.

Motor Torque to
current proportional
constant
0.01 N.m/amb
With neglect inductance:

=
 (10)

= 
. (11)
Fig.2: Equivalent block diagram. [1]
5th IUGRC International Undergraduate Research Conference,
Military Technical College, Cairo, Egypt, Aug 9th Aug 12st, 2021 3
Fig.3: MATLAB Simulink model of DC-servo motor
Fig.4: Plot of angle vs. motor voltage.
It is noted from the response of close loop servo motor without
PID controller that there is a positive relationship between the
motor voltage and the angle.
IV. PID CONTROLLER
It is to note that a developed model of human robot hand
consists of 19 joints. This is very complex, and a few
assumptions have been made to simplify the work. For
instance, friction and stickingare not taken into consideration
for modeling [7]. This allows the conventional PID control to
perform a simple grasping task. In brief, Position control of
servo systems is normally unstable when they are
implemented in closed loop configuration so PID controller is
used to improve the dynamic performance and also reduce the
steady state error of the systems. The block diagram of PID
control is shown below Fig.5
The output of The PID controller (U (t)) is given by: [8]
U(t) = () + +
 e (t). (12)
Where ,, are proportional, Integral and derivative
gains and e (t) =error=set point-output
The PID output in Frequency domain can be represented as

 = +
 + (13)
The closed loop Transfer Function is given by:

=
 H(s)=1 (14)
Y(s) =Output response(s) =input, G(s) =plant
And H(s) =controller.
TABLE II: PID-CONTROLLER GAINS.



The transfer function of closed circle DC-servo motor with
PID controller:
T.F=G(s)= 
 (15)
Fig.5: PID-controller block diagram.
Algorithm of Servo Motor:
1. Determined the input values.
2. Calculated the transfer function plant for Servo DC
motor without PID control of the Close Loop: from
the equation (9).
3. Calculated the transfer function for Servo DC motor
with PID control using step unit of the close Loop:
from the equation (15).
4. Drawing in MATLAB.
V. SIMULATION
The simulation is carried out in MATLAB Simulink. The
actual position and the output is the driven voltage to the
motor. Fig.7,8 shown simulation of servo with PID controller
add its response.
5th IUGRC International Undergraduate Research Conference,
Military Technical College, Cairo, Egypt, Aug 9th Aug 12st, 2021 4
Fig.7: MATLAB Simulink model of DC-servo motor with PID-controller.
Fig.8: Plot of DC-servo motor with PID-controller.
The characteristic for servo DC motor with PID controller for
close loop is stable without error and less over shoot.
Test motor stability: by adding disturbance for motor. This
experiment shows that the system is stable at Fig9, 10.
Fig.9: MATLAB Simulink model of DC-servo motor with PID-controller and
loading disturbance.
Fig.10: Response of DC-servo motor with PID-controller and loading
disturbance
It can be noted that the system under disturbance when step
time is 5 sec there is disturbance founded by (-0.2) detract
from the system response and back stable after removing the
disturbance.
VI. IMPLEMENTATION
A. Control System
The motor is simulated and calculated transfer
function with PID controller. The real control system consists
of actuator (DC-servo motors) and the process (angle).The
potentiometer is the system feedback and gives
microcontroller signal to interface with MATLAB. The
schematic for the system is shown in Fig11.
Fig.11: Schematic of control system for DC servo motor.
The system is stable and ready to connect with real control
system as shown in Fig.12.
Fig.12: Humanoid robot arm with Microcontroller and MATLAB.
The practical experiment [9], the actuator (DC-servo
motor) is connected to power supply and gave feedback to
microcontroller. Our microcontroller is Arduino-Mega
which makes an interface between input and output. The
5th IUGRC International Undergraduate Research Conference,
Military Technical College, Cairo, Egypt, Aug 9th Aug 12st, 2021 5
PID controller takes error signal from MATLAB and
calculates the PWM signal that motor received by
microcontroller.
Now, the different activities could be applied using the
humanoid robot arm safely as shown at Fig.13,14,15.
Fig.13: Free body diagram of humanoid robot arm.
Fig.14: Implementation position control of servo motor to humanoid robot
arm
Fig.15: Humanoid robot arm under control.
VII. CONCLUSIONS
In this paper, distinctive PID controlleris work for
controlling a servo DC motor framework and
implementation for humanoid arm robot.This dual feedback
control provides for a faster response time of the armature
throughout its total voltage range together with the feature
of a position for different voltages. The disturbance is
added to help in checking stability of the system. Analysis
of walking gait, optimal control of multiple motors or other
actuators, controlling the Degree of Freedom (DOF),
adaptability control and intelligence are also the challenging
tasks to make Humanoid robots behave like a human.
ACKNOWLEDGMENT
First and foremost, I would like to thank God Almighty for
giving me the strength, knowledge, ability and opportunity to
undertake this research study and to persevere and complete it
satisfactorily. Without his blessings, this achievement would
not have been possible. The success of this step required a lot
of guidance and assistance from Assoc. Prof. Abdelrady
Okasha Elnady, head of Mechatronics Department Faculty of
Engineering October 6th University and I would like to thank
him for giving me all support and guidance.
5th IUGRC International Undergraduate Research Conference,
Military Technical College, Cairo, Egypt, Aug 9th Aug 12st, 2021 6
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[3] Sailan, Khaled, and Klaus-Dieter Kuhnert. "DC motor
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[4] Global Water Crisis : the Facts,” pp. 13, 2017,
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[5] A. Intelligence, K. Cs, and A. Intelligence, Human Arm
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[6] A. Alim and T. Abubokar, Control of separately excited
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Dynamic and Closed-Loop Control
  • C W Rowley
  • B A Batten
C. W. Rowley and B. A. Batten, "Dynamic and Closed-Loop Control," Fundam. Appl. Mod. Flow Control, vol. 231, pp. 115-148, 2009, doi: 10.2514/5.9781563479892.0115.0148.