Actuators

In mechatronic systems, actuators perform the final stage of the system’s classified tasks.

Microprocessors decide how the system should behave according to sensor data.

Actuators implement that behavior.

A mechatronic system performs basic operations such as motion, energy transmission and energy conversion through actuators.

Electric motors are commonly used for linear movement and positioning.

Hydraulic actuators are used when heavy loads must be lifted precisely.

Electrical Actuators

Convert an electrical signal into mechanical motion.

Examples include stepper motors, solenoid valves, mechanical switches, diodes, thyristors, transistors and relays.

Solenoids

Convert an electrical signal or current into linear mechanical motion.

When the circuit is completed, the coil is energized and the resulting electromagnetic force moves the core axially.

Applications include automobile door locks, washing-machine door locks, latches, solenoid valves and directional-control valves.

Solenoid valves control hydraulic or pneumatic flow.

On-Off Systems for Electrical Devices

Mechanical switches contain one or more contacts that open and close an electrical circuit.

A switch can be operated manually or automatically by pressure, temperature, flow or liquid level.

Relays resemble solenoids in structure and operating principle and open or close an electrical circuit according to an input signal.

Electric Motors

Convert electrical energy into mechanical energy.

Form the basis of many drive systems.

Direct-Current Motors

The rotor is the rotating magnetic cylindrical component around which windings are placed.

The stator is the fixed component that produces the magnetic field acting on the rotor.

The commutator connects to the rotor windings and changes current direction.

Brushed DC motors receive energy from a DC source through carbon brushes.

Brushless DC motors instead use a permanent-magnet rotor and a wound stator.

Alternating-Current Motors

Generally operate without brushes.

Are more reliable and robust than many brushed DC motors.

Require little maintenance.

Can be single-phase or multiphase.

Types include induction, synchronous and asynchronous motors.

The behavior of AC synchronous motors can be controlled with variable frequency.

Stepper Motors

Convert electrical pulses into discrete rotor movements called steps.

Are a special form of permanent-magnet or variable-reluctance motor.

A motor with one degree per step requires 360 pulses for one revolution.

Typically operate at low speed and low torque.

Are suitable for precise motion control.

Can produce movement corresponding to complete revolutions or fractions of a revolution.

Hydraulic and Pneumatic Actuators

Use fluids stored under pressure and transmitted through pipes.

A liquid medium forms a hydraulic system; a gas medium forms a pneumatic system.

They are used widely in machine tools and robots.

They can be better than electrical actuators when handling fragile or soft objects.

Cylinders convert fluid power into linear mechanical motion.

Hydraulic motors convert hydraulic-fluid power into angular motion and torque.

Pneumatic systems are generally cleaner, easier to maintain and in some applications safer than hydraulic systems.

Compressed-air pressure is lower than typical hydraulic pressure, so pneumatic systems produce lower forces.

Hydraulic and Pneumatic System Elements

Energy input

Energy modulation

Energy output

Mechanical Actuators

Also known as power- and motion-transmission elements.

Can change the form and characteristics of motion.

Convert between linear and angular motion

Change rotational speed

Change torque

Change speed and acceleration

Gear Systems

Transmit rotary motion and torque from one shaft to another.

Contain at least a driving gear and a driven gear.

Tooth count, rotational speed and torque depend on the system and together determine the transmission ratio.

Spur gears have parallel shaft axes and teeth parallel to the axis.

Helical gears have parallel shaft axes but teeth wrapped helically around the gear.

Bevel gears are used where shaft axes intersect.

A worm-and-wheel mechanism combines a screw-like member with a gear.

Rack-and-Pinion Mechanisms

Convert between linear and rotary motion.

Consist of a gear and a toothed prismatic rack.

Travel can be calculated from tooth count, number of revolutions and pitch.

Ratchet Mechanisms

Permit rotation in one direction and prevent reverse rotation.

Friction-Wheel Systems

Contain two wheels in contact.

The wheels apply pressure at their contact surfaces, producing friction that transmits motion.

If the friction force is not greater than the transmitted tangential force, slipping occurs and motion cannot be transmitted.

Cam Mechanisms

Produce a desired linear movement from rotary motion.

Consist of a rotating cam and a follower that converts the motion to linear form.

Belt-and-Pulley Mechanisms

Transmit motion with a belt wrapped around driving and driven pulleys.

The belt requires suitable tension and friction against the pulleys.

The transmission ratio can vary.

Chain Mechanisms

Resemble belt-and-pulley systems.

Use sprockets instead of pulleys and a chain instead of a belt.

Can transmit motion between shafts separated by a long distance.

The transmission ratio is fixed.

Crank-and-Connecting-Rod Mechanisms

Convert the reciprocating motion of a piston in an internal-combustion engine into rotation of the crankshaft.

The motion of a shaping machine can also be produced with this mechanism.