TSM 363 Fluid Power Systems

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TSM 363 Fluid Power Systems

• Electronic Controls in Hydraulics Systems

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Automated Functions A Technical Trend
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E/H Systems (Conventional Design)
M
Controller
M
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E/H Systems (Programmable Design)
M
Controller
M
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Basic Electrical Devices

• Seven devices commonly used in the control of
  electrohydraulic systems
• Push-button switches
• Limit switches
• Pressure switches
• Drivers (Servo or Solenoids)
• Relays
• Timers
• Temperature switches

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E/H Control Valves

• On/Off solenoid
• Proportional Solenoid
• Low cost
• PWM control of the solenoid
• Advanced controls
• Servo Valves
• Torque motors
• Costly, limited applications

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Option 1 Solenoid E/H Valve
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Commonly Used Proportional Solenoid Drivers
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Pulse-Width Modulation (PWM) Signal
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Characteristics of PWM Signals

• Amplifier acts as a variable resistance to power
  solenoid
• Voltage fully-on
• Amplifier has zero resistance, no heat build-up
• Maximum voltage to solenoid
• Voltage fully-off
• No power to amplifier, no heat buildup
• High pulse-rate signal of full-on/full-off
• Pulse rate is faster than the solenoid can react
• Solenoid sees these as an average voltage

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Option 2 Two Stage E/H Valve
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Option 3 Servo E/H Valve

• Servo mechanism
• Electric motor
• Position feedback potentiometer
• Reduction gear
• Actuator arm

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Open Loop Control Circuits

• Simple circuit with no measurement of the
  performance at various settings

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Closed-Loop Control

• Feedback enhances performance
• Dynamic response and stability

reference command
output
System dynamics

Controller
-
feedback
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Example of E/H Controls
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Properties of Valve Response Deadband
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Properties of Valve Response Saturation
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Properties of Valve Response Hysteresis
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Properties of Valve Response Stability
Response
Time
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Lecture Summary

• Discussed the basic principles of
  electro-mechanical drivers for E/H valves
• Solenoid driver
• Servo driver
• Introduced a few key parameters describing the
  performance of an E/H valve
• Deadband
• Saturation
• Hysteresis