Actuators

INDIAN INSTITUTE OF ROBOTICS
www.indianinstituteofrobotics.com , info@iir.co.in
1. ACTUATORS
1.1 INTRODUCTION
Actuators Drive motions in mechanical systems. Most often this is by converting electrical
energy into some form of mechanical motion.
1.2 SOLENOIDS
Solenoids are the most common actuator components. The basic principle of operation is there is
a moving ferrous core (a piston) that will move inside wire coil as shown in Figure 1. Normally
the piston is held outside the coil by a spring. When a voltage is applied to the coil and current
flows, the coil builds up a magnetic field that attracts the piston and pulls it into the center of the
coil. The piston can be used to supply a linear force. Well known applications of these include
pneumatic values and car door openers.
Topics:
Objectives:
• Be aware of various actuators available.
• Solenoids, valves and cylinders
• Hydraulics and pneumatics
FIGURE 1: A SOLENOID
As mentioned before, inductive devices can create voltage spikes and may need snubbers,
although most industrial applications have low enough voltage and current ratings they can be
connected directly to the PLC outputs. Most industrial solenoids will be powered by 24Vdc and
draw a few hundred mA.
1.3 VALVES
The flow of fluids and air can be controlled with solenoid controlled valves. An example of a
solenoid controlled valve is shown in Figure 2. The solenoid is mounted on the side. When
actuated it will drive the central spool left. The top of the valve body has two ports that will be
connected to a device such as a hydraulic cylinder. The bottom of the valve body has a single
pressure line in the center with two exhausts to the side. In the top drawing the power flows in
Current Off
Current On

through the center to the right hand cylinder port. The left hand cylinder port is allowed to exit
through an exhaust port. In the bottom drawing the solenoid is in a new position and the pressure
is now applied to the left hand port on the top, and the right hand port can exhaust. The symbols
to the left of the figure show the schematic equivalent of the actual valve positions. Valves are
also available that allow the valves to be blocked when unused.
Figure 2: A Solenoid Controlled 5 Ported, 4 Way 2 Position Valve
Valve types are listed below. In the standard terminology, the ’n-way’ designates the number of
connections for inlets and outlets. In some cases there are redundant ports for exhausts. The
normally open/closed designation indicates the valve condition when power is off. All of the
valves listed are two position valve, but three position valves are also available.
2-way normally closed - these have one inlet, and one outlet. When unenergized, the valve is
closed. When energized, the valve will open, allowing flow. These are used to permit flows.
2-way normally open - these have one inlet, and one outlet. When unenergized, the valve is
open, allowing flow. When energized, the valve will close. These are used to stop flows. When
system power is off, flow will be allowed.
3-way normally closed - these have inlet, outlet, and exhaust ports. When unenergized, the
outlet port is connected to the exhaust port. When energized, the inlet is connected to the outlet
port. These are used for single acting cylinders.
3-way normally open - these have inlet, outlet and exhaust ports. When unenergized, the inlet is
connected to the outlet. Energizing the valve connects the outlet to the exhaust. These are used
for single acting cylinders
3-way universal - these have three ports. One of the ports acts as an inlet or outlet, and is
connected to one of the other two, when energized/unenergized. These can be used to divert
flows, or select alternating sources.
The solenoid has two positions and
when actuated will change the
direction that fluid flows to the device.
The symbols shown here are
commonly used to represent this type
of valve.

4-way - These valves have four ports, two inlets and two outlets. Energizing the valve causes
connection between the inlets and outlets to be reversed. These are used for double acting
cylinders.
Some of the ISO symbols for valves are shown in Figure 3. When using the symbols in drawings
the connections are shown for the un-energized state. The arrows show the flow paths in
different positions. The small triangles indicate an exhaust port.
Figure 3: ISO Valve Symbols
When selecting valves there are a number of details that should be considered, as listed below.
pipe size - inlets and outlets are typically threaded to accept NPT (national pipe thread).
flow rate - the maximum flow rate is often provided to hydraulic valves.
operating pressure - a maximum operating pressure will be indicated. Some valves will also
require a minimum pressure to operate.
electrical - the solenoid coil will have a fixed supply voltage (AC or DC) and current.
response time - this is the time for the valve to fully open/close. Typical times for valves range
from 5ms to 150ms.
enclosure - the housing for the valve will be rated as,
type 1 or 2 - for indoor use, requires protection against splashes
type 3 - for outdoor use, will resists some dirt and weathering
type 3R or 3S or 4 - water and dirt tight
type 4X - water and dirt tight, corrosion resistant
Two Way Two Position
Three Way Two Position
Four Way Two Position

1.4 CYLINDERS
A cylinder uses pressurized fluid or air to create a linear force/motion as shown in Figure 4. In
the figure a fluid is pumped into one side of the cylinder under pressure, causing that side of the
cylinder to expand, and advancing the piston. The fluid on the other side of the piston must be
allowed to escape freely - if the incompressible fluid was trapped the cylinder could not advance.
The force the cylinder can exert is proportional to the cross sectional area of the cylinder.
For Force:
where,
P = the pressure of the hydraulic fluid
A = the area of the piston
F = the force available from the piston rod
Figure 4: A Cross Section of a Hydraulic Cylinder
Single acting cylinders apply force when extending and typically use a spring to retract the
cylinder. Double acting cylinders apply force in both direction.

Figure 5: Schematic Symbols for Cylinders
Magnetic cylinders are often used that have a magnet on the piston head. When it moves to the
limits of motion, reed switches will detect it.
1.5 HYDRAULICS
Hydraulics use incompressible fluids to supply very large forces at slower speeds and limited
ranges of motion. If the fluid flow rate is kept low enough, many of the effects predicted by
Bernoulli’s equation can be avoided. The system uses hydraulic fluid (normally an oil)
pressurized by a pump and passed through hoses and valves to drive cylinders. At the heart of the
system is a pump that will give pressures up to hundreds or thousands of psi. These are delivered
to a cylinder that converts it to a linear force and displacement.
Hydraulic systems normally contain the following components;
1. Hydraulic Fluid
2. An Oil Reservoir
3. A Pump to Move Oil, and Apply Pressure
4. Pressure Lines
5. Control Valves - to regulate fluid flow
6. Piston and Cylinder - to actuate external mechanisms
The hydraulic fluid is often a non corrosive oil chosen so that it lubricates the components. This s
normally stored in a reservoir as shown in Figure 6. Fluid is drawn from the reservoir to a pump
where it is pressurized. This is normally a geared pump so that it may deliver fluid at a high
pressure at a constant flow rate. A flow regulator is normally placed at the high pressure outlet
from the pump. If fluid is not flowing in other parts of the system this will allow fluid to
recirculate back to the reservoir to reduce wear on the pump. The high pressure fluid is delivered
single acting spring return
cylinder
double acting cylinder

to solenoid controlled vales that can switch fluid flow on or off. From the vales fluid will be
delivered to the hydraulics at high pressure, or exhausted back to the reservoir.
Figure 6: A Hydraulic Fluid Reservoir
Hydraulic systems can be very effective for high power applications, but the use of fluids, and
high pressures can make this method awkward, messy, and noisy for other applications.
1.6 PNEUMATICS
Pneumatic systems are very common, and have much in common with hydraulic systems with a
few key differences. The reservoir is eliminated as there is no need to collect and store the air
between uses in the system. Also because air is a gas it is compressible and regulators are not
needed to recirculate flow. But, the compressibility also means that the systems are not as stiff or
strong. Pneumatic systems respond very quickly, and are commonly used for low force
applications in many locations on the factory floor.
Some basic characteristics of pneumatic systems are,
- stroke from a few millimeters to meters in length (longer strokes have more springiness
- the actuators will give a bit - they are springy
- pressures are typically up to 85psi above normal atmosphere
- the weight of cylinders can be quite low

- additional equipment is required for a pressurized air supply- linear and rotatory
actuators are available.
- dampers can be used to cushion impact at ends of cylinder travel.
When designing pneumatic systems care must be taken to verify the operating location. In
particular the elevation above sea level will result in a dramatically different air pressure. For
example, at sea level the air pressure is about 14.7 psi, but at a height of 7,800 ft (Mexico City)
the air pressure is 11.1 psi. Other operating environments, such as in submersibles, the air
pressure might be higher than at sea level.
Some symbols for pneumatic systems are shown in Figure 7. The flow control valve is used to
restrict the flow, typically to slow motions. The shuttle valve allows flow in one direction, but
blocks it in the other. The receiver tank allows pressurized air to be accumulated. The dryer and
filter help remove dust and moisture from the air, prolonging the life of the valves and cylinders.
Figure 7: Pneumatics Components
Flow control valve
Shuttle Valve
Receiver Tank
Pump
Filter
Dryer
Pressure Regulator

1.7 MOTORS
Motors are common actuators, but for logical control applications their properties are not that
important. Typically logical control of motors consists of switching low current motors directly
with a PLC, or for more powerful motors using a relay or motor starter.
1.8 COMPUTERS
- More complex devices contain computers and digital logic.
- to interface to these we use TTL logic, 0V=false, 5V=true
- TTL outputs cards supply power and don’t need a separate power supply
- Sensitive to electrical noise.
1.9 OTHERS
There are many other types of actuators including those on the brief list below.
Heaters - The are often controlled with a relay and turned on and off to maintain a temperature
within a range.
Lights - Lights are used on almost all machines to indicate the machine state and provide
feedback to the operator. most lights are low current and are connected directly to the PLC.
Sirens/Horns - Sirens or horns can be useful for unattended or dangerous machines to make
conditions well known. These can often be connected directly to the PLC.
1.10 SUMMARY
• Solenoids can be used to convert an electric current to a limited linear motion.
• Hydraulics and pneumatics use cylinders to convert fluid and gas flows to limited
linear motions.
• Solenoid valves can be used to redirect fluid and gas flows.
• Pneumatics provides smaller forces at higher speeds, but is not stiff. Hydraulics
provides large forces and is rigid, but at lower speeds.
• Many other types of actuators can be used.
1.11 PRACTICE PROBLEMS
1. A piston is to be designed to exert an actuation force of 120 lbs on its extension stroke. The
inside diameter of the cylinder is 2.0” and the ram diameter is 0.375”. What shop air pressure
will be required to provide this actuation force? Use a safety factor of 1.3.
2. Draw a simple hydraulic system that will advance and retract a cylinder using PLC outputs.
Sketches should include details from the PLC output card to the hydraulic cylinder.
3. Develop an electrical ladder diagram and pneumatic diagram for a PLC controlled system. The
system includes the components listed below. The system should include all required safety and
wiring considerations.
a 3 phase 50 HP motor
1 NPN sensor
1 NO push button
1 NC limit switch
1 indicator light
a doubly acting pneumatic cylinder

1.12 PRACTICE PROBLEM SOLUTIONS
1. A = pi*r^2 = 3.14159in^2, P=FS*(F/A)=1.3(120/3.14159)=49.7psi. Note, if the cylinder were
retracting we would need to subtract the rod area from the piston area. Note: this air pressure is
much higher than normally found in a shop, so it would not be practical, and a redesign would be
needed.
2.
1.13 ASSIGNMENT PROBLEMS
1. Draw a schematic symbol for a solenoid controlled pneumatic valve and explain how the valve
operates.
2. A PLC based system has 3 proximity sensors, a start button, and an E-stop as inputs. The
system controls a pneumatic system with a solenoid controlled valve. It also controls a robot with
a TTL output. Develop a complete wiring diagram including all safety elements.
3. A system contains a pneumatic cylinder with two inductive proximity sensors that will detect
when the cylinder is fully advanced or retracted. The cylinder is controlled by a solenoid
controlled valve. Draw electrical and pneumatic schematics for a system.
4. Draw an electrical ladder wiring diagram for a PLC controlled system that contains 2 PNP
sensors, a NO pushbutton, a NC limit switch, a contactor controlled AC motor and an indicator
light. Include all safety circuitry.
5. We are to connect a PLC to detect boxes moving down an assembly line and divert larger
boxes. The line is 12 inches wide and slanted so the boxes fall to one side as they travel by.
One sensor will be mounted on the lower side of the conveyor to detect when a box is present. A
second sensor will be mounted on the upper side of the conveyor to determine when a larger box
is present. If the box is present, an output to a pneumatic solenoid will be actuated to divert the
box. Your job is to select a specific PLC, sensors, and solenoid valve. Details (the absolute
minimum being model numbers) are expected with a ladder wiring diagram. (Note: take
advantage of manufacturers web sites.)

MOTORS
DC GEARED MOTORS
SPECIFICATIONS
• DC SUPPLY 4 to 12V
• RPM: 10 TO 600 OR MORE
• TOTAL LENGTH : 46 mm
• Motor Diameter : 36 mm
• Motor Length: 25 mm
• Brush Type : Plastic / Metal
• Gear Head Diameter : 37 mm
• Gear Head Length : 21mm
• Output Shaft : Centred
• Shaft diameter: 6mm
• Shaft Length : 22mm
• Gear Assembly : Spur
DC ENCODER MOTORS
1. These DC motors uses 2 phase (quadrature) incremental encoders to detect the speed of
the motor and the distance it has travelled.
2. These motors are designed to run at 6 to 24 volts DC and they draw less than 3 amps
w/locked rotor. (This is normally referred to as the stall current and is usually the
maximum current draw for the motor). Motors are rated at 12 VDC but can be kicked up
to 24 VDC for short periods to get a higher power level if the amplifier used to run the
motor can provide the needed power.
3. Controller and Amplifiers for these motors should be able to provide a continuous current
of 3 amps and extremely short bursts of 6 amps. Popular, amplifiers and controllers
based on the National Semiconductor LMD18200 series chips will do this.

HIGH TORQUE DC GEARED MOTOR
Features:
100RPM 12V DC motors with Metal Gearbox
25000 RPM base motor
6mm shaft diameter
Gearbox diameter 37 mm.
Motor Diameter 28.5 mm
Length 63 mm without shaft
Shaft length 15mm
300gm weight
35kgcm torque
No-load current = 800 mA(Max), Load current = upto 9.5 A(Max)
12V DC geared motors for robotics applications. It gives a massive torque of 35Kgcm.
The motor comes with metal gearbox and off-centered shaft. Shaft has a metal bushing
for wear resisinance.

GEAR MOTOR – 90 DEGREE SHAFT
Features:
Working voltage : 3V to 9V
Compatible wheel available as optional item
40gm weight
Same size motor available in various rpm
3 Kgf.cm torque
No-load current = 60 mA, Stall current = 700 mA
DC geared motor which gives good torque and rpm at lower voltages. This motor can run
at approximately 150 rpm when driven by a single Li-Ion cell.
DUAL SHAFT GEAR MOTOR
This is a low cost low voltage durable dual
shaft DC geared motor. It is most suitable
for light weight robot running on small
voltage. Out of its two shafts one shaft can
be connected to wheel, other can be
connected to the position encoder. Drive
shaft has clutch for non continuous
protection from overload. Motor runs
smoothly from 2V to 9V and gives wide
range of RPM, and torque.
Specifications
· Voltage: 2V to 9V
· Current: No load and stall currents are
function of voltage. Fore more data refer
below tables
· RPM: 20 to 200. RPM is a function of
voltage. For more data refer below tables
· Clutch for non continuous protection from
overload conditions
· Motor weight: 30gms

SERVO MOTORS
• A "servo" is a generic term used for an automatic control system. It comes from
the Latin word "servus" - slave. In practical terms, that means a mechanism that
you can set and forget, and which adjusts itself during continued operation through
feedback. Disk drives, for example, contain a servo system insuring that they spin
at a desired constant speed by measuring their current rotation, and speeding up or
slowing down as necessary to keep that speed.
• The position-sensing mechanism tells the servo what position the shaft currently
has. The control circuitry notes the difference between the desired position and the
current position, and uses the motor to "make it so". If the difference in position is
large, the motor moves rapidly to the correct position; if the difference is small,
the adjustment is more subtle. As for the operator, all he knows is that he moved a
slider half-way up, and the rudder on his model plane moved to the center
position, and will stay there until he moves the slider again.
• The most commonly available servo motors on the market are the range from
Futaba. These include high tech digital servo motors. The regular servo motors
used in radio controlled cars is small and inexpensive. These servo motors are
usually made from plastic and have plastic gears.
• Usually rc servo motors come in standard sizes and have similar control schemes.
Unlike other servo motors rc servo motors are constrained from full rotation. RC
servo motors are restricted to a limited rotation of 180 degrees or less. Standard
servo motors such as the Futaba S148 can undergo mods which are designed to
make it rotate a full 360 degrees.

CONNECTIONS OF A SERVO MOTOR
• a high torque plastic gear servo motor measuring with dual ball bearings. It gives
6.4Kg/cm cm torque. This servo motor is ideal for making your own light weight
hexapod, walking insects, sensor / camera pod etc. Servo motors are used in radio control
models. They are very useful in robotics applications because of there small size and low
cost. Servomotor has built in motor, gearbox, position feedback mechanism and motor
controller. The servo motor can be controlled to move any position just by using simple
pulse controlling. This motor has three wire interfaces for control and power supply
• Specifications
• Dimension: 40.7mm x 20.5mm x39.5mm
• Torque: 6.4kg/cm
• Motor weight: 41gms
• Operating speed: 0.17sec/60 degree
• Operating voltage: 4.8V to 6V
• Temperature range: 0-55C .
HIGH TORQUE RC SERVO MOTOR WITH METAL
GEARS
Specifications :
· Dimension: 40.7mm x 20.5mm x39.5mm
· Torque: 15.5kg/cm at 4.8V, 17kg/cm at 6V
· Dual bearing with metal gear
· Motor weight: 60gms
· Operating speed: 0.15sec/60 degree
· Operating voltage: 4.8V to 6V
· Temperature range: 0-55C

It gives whooping 15.5Kg to 17kg cm torque. This servo motor is ideal for making your own
hexapod, walking insects, heavy duty sensor / camera pod. Servo motors are used in radio
control models. They are very useful in robotics applications because of there small size and low
cost.
Servomotor has built in motor, gearbox, position feedback mechanism and motor controller. The
servo motor can be controlled to move any position just by using simple pulse controlling.
HS 485B DELUX HEAVY DUTY SERVO WITH
KARBONITE GEARS
Specifications :
• Dimension: 39.8mm x 19.8mm x37.8mm
• Torque: 5.2kg/cm at 4.8V, 6.4kg/cm at 6V
• Motor weight: 45gms
• Operating speed: 0.20sec/60 degree
• Operating voltage: 4.8V to 6V
• Temperature range: 0-55C
This is high torque Karbonite gear servo motor measuring 39.8mm x 19.8mm x37.8mm. It gives
5.2Kg to 6.4kg cm torque. This servo motor is suitable for making your own light weight
hexapod, walking insects, heavy duty sensor / camera pod etc. Servo motors are used in radio
control models.
They are very useful in robotics applications because of there small size and low cost.
Servomotor has built in motor, gearbox, position feedback mechanism and motor controller.

Actuators

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (7)

Similaire à Actuators

Similaire à Actuators (20)

Dernier

Dernier (20)

Actuators