Actuator Selection and Power Converters

Actuator Selection

• Actuators convert power into motion
• Power/energy conversion methods include electrical motors (DC, AC, stepper), combustion engines, pressure/flow (hydraulic, pneumatic), and smart materials.
• Transmission components handle power transfer, such as gears, belt drives, and power screws.
• Support components include bearings.
• Structural support components involve frames, shafts, and axles.
• Tools for actuator selection include stress analysis, failure theories, dynamics, statics, and actuator sizing.

Power/Energy Converters (Rotary)

• Electrical input converts to mechanical rotary motion/torque via DC motors, AC motors, stepper motors, and smart materials.
• Combustion (e.g., gasoline engines) generates rotary motion/torque.
• Pressure/flow (e.g., hydraulic and pneumatic actuators) create rotary motion/torque.

Power/Energy Converters (Linear)

• Electrical input yields mechanical linear motion/torque, accomplished using lead screw linear actuators, linear motors, solenoids, and smart materials (SMA, Piezoelectric).
• Pressure/flow inputs lead to mechanical linear motion/torque by utilizing hydraulic actuators (cylinders) and pneumatic actuators (cylinders).

Actuators Power-to-Weight Ratio

• A graph displays power-to-weight ratios for different actuator types, indicating relative performance.
  • Hydraulic actuators are high in power/weight ratio
  • Pneumatic motors are middling
  • Piezoelectric actuators are low

Operational Efficiency

• Actuator types have varying operational efficiencies.
  • Electric motors generally have high efficiency.
  • Servo-hydraulic systems show middling efficiency.
  • Hydraulic motors have lower efficiency.

Operational Efficiency and Energy Conversion (Hydraulic System)

• A hydraulic system diagram tracks power flow from electrical input to hydraulic power to useful output power, noting losses at each stage (VFD, motor, pump, hydraulic system).
• Losses include current, copper, and iron losses in the motor; volumetric and mechanical losses in the pump; and throttling and mechanical losses in the hydraulic system

Operational Efficiency and Energy Conversion (Electrical Motor Actuation System)

• A diagram illustrates the power conversion in an electrical motor system, involving power supply, drive, gearmotor, and load.
• Watts in and out are measured with respect to load
• Electrical power (IV) is converted to mechanical power (Fv or T*w).

Motion Control Capabilities

• A matrix depicts the capabilities of different actuators for various control variables (position, velocity, acceleration/deceleration, and force).
• Electric motors are strong in all areas
• Hydraulic/Servo-Hydraulic systems are best in force application
• Electric motors are strong contenders in Position, Velocity, and Accel/Decel

Power Transmission Comparison Table

• A table comparing pneumatic, hydraulic, and electric power transmission systems across various characteristics (complexity, peak power, size, control, position accuracy, speed, purchase cost, operating cost, maintenance cost, utilities, efficiency, reliability, maintenance).

Electric Motors

• DC motors: efficient for controlling speed & direction via voltage; torque control is easy via current; low voltage; linear torque-speed relationships; quick response.
• AC motors: smaller, more reliable, and cheaper than DC motors; speed is fixed; low starting torque.

Analysis of Electric Motors

• Electric motors transform electrical power into mechanical power.
• I, and V determine Electrical Power
• F and v or T and w determine mechanical Power.

Losses in Electric Motors

• The formulas for electrical and mechanical power losses are shown.

Data Sheet and Operating Ranges

• Various parameters for motors are provided, including voltage, speed, current, torque, and efficiency.

PM DC Motor Constants

• Induced voltage is proportional to motor speed
• Speed constant is the inverse of the induced voltage and motor speed.
• Generator constant is the inverse of motor speed constant

Motor Model

• Motor as an electrical circuit with applied motor voltage U, resistance R, and inductance L.
• Induced voltage Uind, and motor speed (n) are related in a linear equation.

Speed-Torque Curve

• The graph shows the relationship between speed and torque.
• A no-load speed (n0) and torque (M0), rated torque (Mn), and rated speed (nN) are included on the graph
• Relevant formulas for speed, torque and current are displayed

Winding

• Winding series at a constant voltage (U).
• Relationship between winding characteristics, speeds, torque, and current

Nominal Voltages

• Values at nominal voltage, with no-load operating points, rated working points, and motor at stall, which are all used for measuring current, speed, and torque.

Friction and no-Load

• Motor friction torques contain two components (MVA) - constant factor, and (C5) - speed-dependent factor)
• No-load current corresponds with friction torque - good enough in most circumstances.

Data Sheet and Operating Ranges (Page 21)

• Data for voltage, speed, current, torque, and efficiency are presented.

Operating Ranges

• Graph showing motor limits and various operation ranges based on winding temperature limits.
• There are different operating ranges based on ambient temperature and acceptable heat dissipation

Short-term Operation at Overload

• Graph depicting permissible short-term overload operation based on thermal time constant and overload amount.

Influence of Temperature

• Temperature coefficients and their impacts to resistance and magnetic properties are included.

Efficiency

• Graph illustrating maximum efficiency points and formulas based on torque (M) and current (I).

Thermal Motor Data

• Heating and cooling factors, including considerations for mounting conditions, thermal resistance values, time constants, and temperature limits.

Mechanical Motor Data

• Details of maximum permissible speed, bearing considerations (for EC and DC motors), and axial and radial play.

Torque-Speed Curve – Other Motors

• Graph showing torque-speed curves for various motor types (DC, AC, gasoline engine).

Load Lines

• Load lines (working load vs speed) indicate where the motor's operation line and load curve intersect.

Operating Torque Example

• Calculating motor speed and current under no-load, stall conditions, and lifting loads using provided equations.

Operating Torque Example – Solution (Part a, b, c)

• Solutions for specific problems related to operating torque and specific loads are provided with formulas and graphs showing speed vs torque at different current levels.

Operating Modes (Four Quadrant)

• Diagram showing four operating modes of a motor; forward motoring, forward braking, reverse motoring, reverse braking.

Motor Drive Schematic

• Illustrates the components of a typical motor drive system (controller, power converter, motor, load), indicating input values and output parameters.

Control of Electric Machines

• Diagram depicting the control loops for an electric machine (position control loop, velocity control loop).

Questions

• Questions are presented for further clarification.