Characteristics, Specifications & Load Calculation of servomotors

1. ICE 3015: CONTROL SYSTEM
COMPONENTS
Class 4: Characteristics, Specifications
& Load Calculation
Dr. S. Meenatchisundaram
Email: meenasundar@gmail.com
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

2. Torque-Speed Characteristics:
• Separately excited dc servo-motor characteristics is shown
below.
• Their armature is deliberately designed to have large resistance
so that torque speed characteristics are linear and have large
negative slope as shown in figure.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

3. Other Characteristics:
• The instantaneous polarity of control voltage governs the
direction of torque developed by servomotors.
• The variation in torque-speed characteristics due to variation in
temperature is shown in graph.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

4. Torque-Speed Characteristics:
• The curves showed in below figure shows typical speed torque
characteristics of ac servomotor for several values of rotor
resistances.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

5. Torque-Speed Characteristics:
• It can be seen that for higher values of rotor resistance the torque
speed characteristics is linear.
• If the rotor resistance is either R4 or R5, the motor is referred to
as two phase servo motor.
• For servo application the motor characteristics should be linear
with negative slope (With positive damping).
• It can be proved that for stable operation positive damping is
essential.
• Therefore ordinary two phase induction motor with low rotor
resistance is not suitable for servo applications.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

6. Performance Specifications:
To properly size a motor, these specifications must be matched
according to the load requirements of the application.
Shaft speed (RPM) defines the speed at which the shaft
rotates, expressed in rotations per minute (RPM).
Typically, the speed provided by the manufacturer is the no-load
speed of the output shaft, or the speed at which the motor's
output torque is zero.
Terminal voltage refers to the design voltage of the DC
motor.
Essentially the voltage determines the speed of a DC motor, and
speed is controlled by raising or lowering the voltage supplied to
the motor.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

7. Performance Specifications:
• Torque is the rotational force generated by the motor shaft. The
torque required for the motor is determined by the speed-
torque characteristics of the various loads experienced in the
target application.
Starting torque - The torque required when starting the motor,
which is typically higher than the continuous torque.
Continuous torque - The output torque capability of the motor
under constant running conditions.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

8. Typical Specifications:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
items unit Specification
Basic
Specifica
tions
Rated Output * W 50 100 200 400 750 1000 1500 2000 3000 5000
Rated Torque * Nm 0.16 0.32 0.64 1.27 2.39 3.18 4.77 6.37 9.55 15.9
Instantaneous
Peak Torque *
Nm 0.48 0.96 1.91 3.82 7.16 9.55 14.3 19.1 28.6 47.7
Rated Speed * min-1 3000
Max Speed * min-1 5000
Moment of Inertia *
kg-
m2×10-4 0.014 0.023 0.12 0.22 0.62 1.25 1.72 2.06 5.36 8.52
Load Inertia
kg-
m2×10-4 Up to 30 times Motor Inertia Up to 5 times Motor Inertia
Rated Power Rate
*
kW/sec 18.1 44.0 33.8 73.3 92.1 80.9 132 197 170 297
Speed
Positioni
ng
Detector
Standard — 17bit/rev incremental encoder (Serial Output)
Optional — 17bit/rev absolutel encoder (Serial Output)
Time Rating Continuous
Ambient Temperature 0 to +40°C
Ambient Humidity 20 to 90%RH (without dewing)
Vibration 15 um or below
Protection IP55 (excluding the part passed through by the shaft and the connector)
Durability of vibration 24.5m/s2(2.5G), XYZ direction each for 2Hr, from 10Hz to 120Hz
Mounting Flange Mounting

9. Typical Specifications:
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018
Features
• Holding Torque: 70KG-cm
• 400W AC servo performance with FOC AC drive
RMCS-1110
Motor Specifications
• Step Angle : 1.8 Degree, 50 pole
• Configuration: 4 wire bipolar stepper motor, 2-phase
AC
• Rated Voltage: 3.2V
• Phase current: 4.2Amp
• Resistance/phase: 0.44ohm
• Inductance/Phase: 4.4mH
• Rotor inertia: 2700gcm2
• Encoder Resolution(CPR) = 1000
• Insulation Class: Class B
• Length (L): 165mm
• Shaft Dia : 14mm
• Shaft Length : 40mm
• Shipping Weight: 3300grams

10. Load Calculation:
• A 450 g mass is tied with a string which needs to be accelerated
upwards at least 3 m/s². The spindle that pulls up has a radius of 5
cm. Calculate the torque and power requirements.
• Gravity: F=ma
=0.450kg∗9.8m/s2
=4.41N
• Torque for acceleration: (0.450 kg)(3 m/s²) = 1.35 N
• In addition to the 4.4 N just to balance gravity means you need 5.8 N
upwards force.
• T=Fr =5.8N∗0.05 =0.29Nm
• At 0.05 m radius, that comes out to a torque of 0.29 Nm. There will
be some friction and you want some margin, so in this example a 0.5
Nm motor would do it.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018

11. Load Calculation:
Power is another important one. For that you have to decide what's the
fastest speed you want to be able to pull the mass upwards at. Let's
say 2 m/s for sake of example. From above, we know the highest
upwards force is 5.8 N.
(5.8 N)(2 m/s) = 11.6 Nm/s = 11.6 W
After accounting for some losses due to friction and leaving a little
margin, the motor should be rated for about 15 W minimum.
Control System Components (ICE 3015)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2018