Actuators Flashcards
What are the three main sources of energy for actuators?
- Hydraulic (Pressurized Liquid)
- Pneumatic (Compressed Gas)
- Electrical
What is the term we can use to group Hydraulic and Pneumatic actuators?
Fluid Power Systems
What are the two types of Actuators motion?
- Linear - Generating a Translation or Applying a Force
- Rotary - Inducing a Rotation or Applying a Torque
What are the main characteristics we need to consider when characterising fluid power actuators?
- Bore - Cylinder Diameter
- Stroke - How far they can move
What is a common pressure operation range for hydraulic power?
Why is this?
0-6 bar because you will begin to experience leakages at higher pressures
What are the advantages and disadvantages of a hydraulic system?
Advantages:
* We can operate at high pressures (200 bar)
* Hydraulic actuators are stiff due to the fluids incompressibility
* Easy to control in position and speed
Disadvantages:
* Noisy
* High Friction
* Thermal effect (non-linear)
* “Messy” - Leakages of oil and fluids can occur at high pressure, which is why it’s uncommon for useage in the food industry
What are the two main differences between a hydraulic actuator and a pneumatic actuator?
- The fluid for a pneumatic is compressible because we are using gases compared to water
- In the industrial context, we don’t need to have a specific location where we reject the gases used since they are already cleanly in the atmosphere
What are the advantages and disadvantages of a pneumatic system?
Advantages:
* Quick (Fast answer)
* Excellent power to weight ratio
* No return lines needed
* Simple design and control (cheap)
* Fireproof
* Shock absorbant
Disadvantages
* Low working pressure: 5-10 bar
* Difficult to control in position or speed (due to the compressibility of the gas)
* Variation of the pressure due to temperature (PV=nRT)
* Delay (Dependent on the length of the tubing)
What is a pump used for and what type of system is it involved in?
Pumps are used to generate a flow of fluid
They are featured within a hydraulic system
What is a compressor used for and what type of system is it involved in?
Compressors are used to pressurize a gas
They are featured within a pneumatic system
What colours are the arrows for Pneumatic and Hydraulic Systems in a Fluid Power Diagram?
White arrows are used for Pneumatic systems
Black arrows are used for Hydraulic systems
What does a filter do?
Remove debris from the system
What does a lubricator do?
Reduce the friction in the system using a liquid, which is why they aren’t often used in a pneumatic system
What does an air dryer do?
Remove moisture from the air
What does a pressure regulator do?
They maintain a constant pressure in the system. They can do this before or after the system
What is a FRL Unit?
Filter Regulator Lubricator Unit
How do we collect multiple components into one in a fluid power diagram?
We draw a dotted line around the system to collapse it into a subsystem
What are valves used for?
- Change flow direction
- Change flow rate
- Change fluid pressure
What are the types of Spool Valve Actuators?
- Button
- Lever
- Solenoid
What are the 4 things DCV (Directional Control Valves) symbols show?
- The number of ports and the number of switching positions (Inlets and outlets ports are shown by lines)
- The flow path and arrows in the direction of flow
- The shutoff positions indicated by lines drawn at right angles (T)
- The actuation and return actuation method
What is the neutral resting positions of x/2 and x/3 DCV’s when x can be any number?
x/2 = Right
x/3 = Middle
What electrical component is similar to the functionality of a check valve?
Diode
How does a check valve work?
There is a ball that can be pushed to allow flow, but only in one direction. In one way, the ball will be pushed over the valve so no flow can pass, whereas in the other direction, the ball will be pushed out of the way, which will allow flow to pass
What type of logic gate is a shuttle valve similar to?
OR
What type of logic gate is a two pressure valve similar to?
AND
Why do we implement flow control valves?
So we can restrict the flow rate and reduce / prevent damage on the parts
How does a flow control one way valve work?
There is a flow control valve and a check valve. In one direction, the check valve prevents flow, which forces flow into the flow control valve. In the other direction, the check valve allows flow to pass, which means that the flow is relatively normal, since less flow passes through the flow control valve
(Think like electricity with high and low resistances with current splitting)
How does a single acting cylinder work?
There is a valve into the system, where the piston is pushed when the pressure is high. Once the pressure is then dropped, there is a spring that will return the piston to it’s original position
How does a double acting cylinder work?
There is two valves, one infront of the piston head, and one behind. The piston moves depending on the relative pressures on both sides of the head
How does a pressure multiplier work?
There is an inlet valve which pushes a piston. This converts the pressure of the gas into a force that applies to an area. On the other side of the piston, there is a much smaller head. Since the force is a constant, then the pressure will increase with the smaller area, which will mean there’s a greater pressure at the outlet valve
How does a pneumatic motor work?
They use fluid with a flow to generate a rotation on the motor shaft
What is the opposite of a pneumatic motor?
A compressor
What is a solenoid?
Actuators that use an electromagnetic field to move a mechanical part
What is a relay?
A mechanical switch activated by an electromagnetic field
What is the equation of the force applied by an electromagnet?
F = (B^2 * A) / (2 * Magnetic Permiability)
Why can’t a solenoid be used continuously?
Due to thermal effects
What is the formula for duty cycle?
Duty Cycle = Time on / Total time * 100%
What are the three main components of a DC motor?
- A permanent or electromagnet as a stator
- A rotor with an armature (core and windings) with a commutator
- Brushes to connect the rotor to the power supply
Because of Lorentz Force, what assumption can we make about the torque of a motor?
The torque is proportional to the current flowing through the motor
The proportionality is equal to the torque constant
What is the formula that relates the Electrical Input Power and the Developed Mechanical Power?
Voltage in * Current =(Resistance * Current^2) + (Torque * Angular Velocity)
When can we neglect the resistor for a motor?
When we use a motor with a high power (1kW)
What is a H-Bridge?
An electrical circuit used to control change the direction of rotation of a motor
What is the angular velocity of a Synchronous AC Motor?
Angular Velocity = (2 * pi * Frequency) / Pairs of poles
What is the power of a DC motor?
Power = Torque * Angular Velocity
What is the power of a 3-phase motor?
3^0.5 * V * I * Cos(Phase Shift Angle)
What is a soft starter?
A device that progressively increases the current delivered to an AC Motor to prevent a current surge at start
What is a Variable Frequency Drive?
A device that allows varying the frequency of the AC signal to change the speed of AC motors
What happens to a stepper motor when two phases are switched on simultaneously?
The rotor will go to the middle between these two phases
What is Microstepping?
Making steps between phases by triggering multiple phases at multiple strengths. It reduces the torque and strength of the motor slightly, but we can make smaller steps
What are some mechanisms to convert a rotation to a translation?
- Screw
- Rack and pinion
- Pulley and belt
