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Solenoids, DC Motors
And the fine art of Snubbing
CMPE 118 MECHATRONICS
Solenoids
CMPE 118 MECHATRONICS
Most Common Solenoid Types
Pull
Push
CMPE 118 MECHATRONICS
Open-Frame
Rotary
Solenoid Characteristics
CMPE 118 MECHATRONICS
Design Affects Stroke vs. Force Characteristic
CMPE 118 MECHATRONICS
Typical Solenoid Specifications
CMPE 118 MECHATRONICS
DC Motors provide Rotary Motion
Where do you find them?
CMPE 118 MECHATRONICS
CMPE 118 MECHATRONICS
The Permanent Magnet DC Motor
CMPE 118 MECHATRONICS
Commutation
CMPE 118 MECHATRONICS
Electrical Model of a DC Motor
CMPE 118 MECHATRONICS
Deriving some useful relationships
CMPE 118 MECHATRONICS
More Room for Derivations
CMPE 118 MECHATRONICS
Torque vs. Speed
CMPE 118 MECHATRONICS
Power vs. Torque
How Does P change with V at Constant T?
CMPE 118 MECHATRONICS
Where is PMAX and What is its Value?
CMPE 118 MECHATRONICS
Torque vs. Everything
CMPE 118 MECHATRONICS
DC Motor Specifications
CMPE 118 MECHATRONICS
Operating Ranges
CMPE 118 MECHATRONICS
Defining ‘Short Term Operation’
CMPE 118 MECHATRONICS
CMPE-118 DC Motor Lecture Problem
You have been assigned to follow up on the design of a former employee who had
not taken CMPE-118. Your supervisor suspects that they didn't know what they
were doing. The only documentation that you can find shows that the motor chosen
has Kt = 9.33 in.-oz./A and produces 2.8 in.-oz. at stall when driven at 12V. The
design requires that the motor deliver 0.4 in.-oz. at 1500 rpm. The motor was
supposed to be driven from a 12V supply and switched by a ULN2003. Your boss
has asked you:
a) How can I find out how much current the motor will draw at stall ?
b) Can the ULN2003 safely switch the required current?
c) How can I find the NL Speed ?
d) How can I find the coil resistance ?
e) How can I find the torque at a given speed ?
f) Will the design meet the requirements for torque & speed? If not, what changes
could you suggest?
g) To estimate the current required when running at the design point.
You may assume that there are no internal losses within the motor.
KT = 1.3524KE [oz-in/A ; V/krpm]
CMPE 118 MECHATRONICS
Motor Design Solution
Kt = 9.33 in.-oz./A
Tstall = 2.8 in.-oz.
Vstall = 12V.
Treq = 0.4 in.-oz.
wreq =1500 rpm.
KT = 1.3524KE [oz-in/A ; V/krpm]
CMPE 118 MECHATRONICS
Directional Control
With a Single Power Supply
The H-Bridge
CMPE 118 MECHATRONICS
Pulse Width Modulation
CMPE 118 MECHATRONICS
DC Motor Drive Simulation
12V
+V
1.2mH
11.4
0/0V
50
Ext
CMPE 118 MECHATRONICS
File
2N3055
Drive Waveform
5.2
4.3
3.4
Volts
2.5
1.6
700m
-200m
0
167u
333u
500u
Ref=Ground X=167uS/Div
CMPE 118 MECHATRONICS
667u
833u
1m
Transistor Current
1.06
877m
Current (A)
694m
510m
326m
143m
-40m0
167u
CMPE 118 MECHATRONICS
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m
Inductor Current
47.2m
-137m
-322m
-507m
-692m
-876m
-1.06
0
167u
333u
500u
Ref=Ground X=167uS/Div
CMPE 118 MECHATRONICS
667u
833u
1m
Collector Voltage
223
Volts
184
146
107
68.1
29.4
0
0
CMPE 118 MECHATRONICS
167u
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m
Diode Snubber
12V
+V
1.2mH
11.4
0/0V
50
Ext
CMPE 118 MECHATRONICS
File
2N3055
DIODE
Collector Voltage w/ Diode Snubber
13.3
11
Volts
8.74
6.43
4.13
1.82
-479m0
167u
333u
500u
Ref=Ground X=167uS/Div
CMPE 118 MECHATRONICS
667u
833u
1m
Inductor Current w/ Diode Snubber
40.8m
Current(A)
-143m
-326m
-510m
-694m
-877m
-1.06 0
CMPE 118 MECHATRONICS
167u
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m
How would we add diodes
to protect the H-Bridge?
CMPE 118 MECHATRONICS
12V
+V
1.2mH
Diode + Zener Diode Snubber
DIODE
ZENER
11.4
0/0V
50
Ext
CMPE 118 MECHATRONICS
File
2N3055
Collector Voltage with Diode + Zener Snubber
39.9
Voltage
33
26.1
19.2
12.3
5.4
-1.5 0
167u
CMPE 118 MECHATRONICS
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m
Inductor Current with Diode + Zener Snubber
42.5m
Current
-141m
-325m
-509m
-693m
-877m
-1.06 0
167u
CMPE 118 MECHATRONICS
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m
+V
1.2mH
Zener Only Snubber
11.4
0/0V
50
2N3055
1N4749
Ext
CMPE 118 MECHATRONICS
File
Collector Voltage with Zener Only Snubber
36
Voltage
29.7
23.5
17.3
11.1
4.87
-1.35 0
167u
CMPE 118 MECHATRONICS
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m
Inductor Current Decay Comparison
47.6m
Diode Only
-137m
Resistor + Diode
Zener Only
Current
-321m
Diode + Zener
No Snubber
-506m
-690m
-875m
-1.06
303u
372u
CMPE 118 MECHATRONICS
442u
511u
580u
Ref=Ground X=69.2uS/Div 241%
649u
718u
How would we add Zener diodes
to protect the H-Bridge?
CMPE 118 MECHATRONICS
The Brushless DC Motor
CMPE 118 MECHATRONICS
Commutating a Brushless DC Motor
CMPE 118 MECHATRONICS
Hall Sensor Based Commutation
CMPE 118 MECHATRONICS
Brushed vs. Brushless DC Motors
Mechanical Structure
Commutation Method
Brushed Motor
Brushless Motor
Field Magnets on stator
Windings on Rotor
Field Magnets on Rotor
Windings on stator
Mechanical contact between
brushes and commutator
added friction, brush debris,
RFI
Electronic switching using transistors
low frequency harmonics due to ripple
Rotor Position Detection Automatically detected by
Reversing Method
Distinctive Features
CMPE 118 MECHATRONICS
brushes
Hall Element, optical encoder, Back
EMF
Reverse terminal voltage
Rearrange logic sequencer
Quick response
Excellent controllability
Current limited by
brush/commutator interface
Speed limited by brush bounce
Long Lasting
Easy or no maintenance
Current limited by winding resistance
only
No fundamental high frequency
(speed) limit
Usually more efficient than brushed
Inductor Current with Zener Only Snubber
41m
Current
-143m
-326m
-510m
-694m
-877m
-1.06 0
167u
CMPE 118 MECHATRONICS
333u
500u
Ref=Ground X=167uS/Div
667u
833u
1m