Robotics and automation _ power sources and sensors

Unit 2 – Power Sources and
Sensors

Syllabus
• Robotic Drives
– Hydraulic
– Pneumatic
– Electric
• Actuators
– Hydraulic
– Pneumatic
– Electric
• Determination of HP of motor and gearing ratio
• Variable speed arangements
• Path determination
• Micro machines in robotics
• Machine vision
• Sensors in robotics

Robotic Drives
• A robot will require a drive system for moving
their arm, wrist, and body.
• The joints are moved by actuators powered by
a particular form of drive system.
• A drive system can also be used to determine
the capacity of a robot.
• there are three different types of drive systems
available such as:
– Hydraulic drive system,
– Pneumatic drive system, and
– Electric drive system,

Hydraulic Drive Systems:
• A hydraulic drive system is a quasi-
hydrostatic drive or transmission system that
uses pressurized hydraulic fluid to
power hydraulic machinery
• A hydraulic drive system consists of three
parts:
– The generator (e.g. a hydraulic pump), driven by
an electric motor;
– valves, filters, piping etc. (to guide and control the
system);and
– The actuator (e.g. a hydraulic motor or hydraulic
cylinder) to drive the machinery.

Examples of Hydraulic Drive Systems

Pneumatic Drive System
• Pneumatic systems use air as the medium
which is abundantly available and can be
exhausted into the atmosphere after
completion of the assigned task
• The pneumatic drive systems are especially
used for the small type robots, which have
less than five degrees of freedom.

Components of Pneumatic Drive
Systems

Components of Pneumatic Drive
Systems
• Air filters: These are used to filter out the contaminants from the air.
• Compressor: Compressed air is generated by using air compressors. Air
compressors are either diesel or electrically operated. Based on the
requirement of compressed air, suitable capacity compressors may be
used.
• Air cooler: During compression operation, air temperature increases.
Therefore coolers are used to reduce the temperature of the compressed
air.
• Dryer: The water vapor or moisture in the air is separated from the air by
using a dryer.
• Control Valves: Control valves are used to regulate, control and monitor
for control of direction flow, pressure etc.
• Air Actuator: Air cylinders and motors are used to obtain the required
movements of mechanical elements of pneumatic system.
• Electric Motor: Transforms electrical energy into mechanical energy. It is
used to drive the compressor.
• Receiver tank: The compressed air coming from the compressor is stored
in the air receiver.

Electric Drive Systems
• The electric drive systems are capable of
moving robots with high power or speed.
• The actuation of this type of robot can be
done by either DC servo motors or DC
stepping motors.

Actuators
• Actuators can be categorized by the energy
source they require to generate motion. For
example:
– Hydraulic actuators use liquid to generate
motion.
– Pneumatic actuators use compressed air to
generate motion.
– Electric actuators use an external power
source, such as a battery, to generate motion.

Advantages
• Hydraulic actuators are rugged and suited for high-force
applications. They can produce forces 25 times greater
than pneumatic cylinders of equal size. They also operate
in pressures of up to 4,000 psi.
• Hydraulic motors have high horsepower-to-weight ratio by
1 to 2 hp/lb greater than a pneumatic motor.
• A hydraulic actuator can hold force and torque constant
without the pump supplying more fluid or pressure due to
the incompressibility of fluids
• Hydraulic actuators can have their pumps and motors
located a considerable distance away with minimal loss of
power.

Disadvantages
• Hydraulics will leak fluid. Like pneumatic
actuators, loss of fluid leads to less efficiency.
However, hydraulic fluid leaks lead to cleanliness
problems and potential damage to surrounding
components and areas.
• Hydraulic actuators require many companion
parts, including a fluid reservoir, motors, pumps,
release valves, and heat exchangers, along with
noise-reduction equipment. This makes for linear
motions systems that are large and difficult to
accommodate.

Pneumatic Actuator
• Pneumatic actuators are the devices used
for converting pressure energy of
compressed air into the mechanical energy
to perform useful work.

Types Of Pneumatic Actuators
• There are three types of pneumatic actuator:
they are
– Linear Actuator or Pneumatic cylinders
– Rotary Actuator or Air motors
– Limited angle Actuators

Advantages
• The benefits of pneumatic actuators come from their
simplicity.
• Pneumatic actuators generate precise linear motion
by providing accuracy, for example, within 0.1 inches
and repeatability within .001 inches.
• Pneumatic actuators typical applications involve
areas of extreme temperatures.
• In terms of safety and inspection, by using air,
pneumatic actuators avoid using hazardous
materials. They meet explosion protection and
machine safety requirements because they create no
magnetic interference due to their lack of motors.

Disadvantages
• Pressure losses and air’s compressibility make
pneumatics less efficient than other linear-motion
methods. Compressor and air delivery limitations mean
that operations at lower pressures will have lower forces
and slower speeds. A compressor must run continually
operating pressure even if nothing is moving.
• To be truly efficient, pneumatic actuators must be sized
for a specific job. Hence, they cannot be used for other
applications. Accurate control and efficiency requires
proportional regulators and valves, but this raises the
costs and complexity.
• Even though the air is easily available, it can be
contaminated by oil or lubrication, leading to downtime
and maintenance.

Electric Actuators
• Electric Actuators are devices powered by
motor that converts electrical energy to
mechanical torque
Types Of Electric Actuators
• There are three types of pneumatic actuator:
they are
– DC Motors- is an electric motor that runs on direct
current (DC) electricity.
– AC Motors - is an electric motor driven by an
alternating current.
– Stepper Motors- (or step motor) is a brushless DC
electric motor that divides a full rotation intoa
number of equal steps.

Advantages
• Electrical actuators offer the highest precision-control
positioning.
• Their setups are scalable for any purpose or force
requirement, and are quiet, smooth, and repeatable.
• Electric actuators can be networked and reprogrammed
quickly. They offer immediate feedback for diagnostics
and maintenance.
• They provide complete control of motion profiles and
can include encoders to control velocity, position, torque,
and applied force.
• In terms of noise, they are quieter than pneumatic and
hydraulic actuators
• Because there are no fluids leaks, environmental hazards
are eliminated.

Disadvantages
• The initial unit cost of an electrical actuator is
higher than that of pneumatic and hydraulic
actuators.
• Electrical actuators are not suited for all
environments, unlike pneumatic actuators,
which are safe in hazardous and flammable
areas
• A continuously running motor will overheat,
increasing wear and tear on the reduction gear.
• The motor can also be large and create
installation problems.

Horsepower
• Horsepower (hp) is a unit of
measurement of power (the rate at
which work is done). There are many different
standards and types of horsepower. Two
common definitions being used today are
the mechanical horsepower (or imperial
horsepower), which is about 745.7 watts, and
the metric horsepower, which is
approximately 735.5 watts.

Calculation of 5252
• constant tangential force of 100 pounds was applied
to the 12" handle rotating at 2000 RPM,
POWER = FORCE x DISTANCE ÷ TIME
DISTANCE per revolution = 2 x π x radius
DISTANCE per revolution. = 2 x 3.1416 x 1 ft = 6.283 ft.
Now we know how far the crank moves in one revolution. How far does the
crank move in one minute?
DISTANCE per min. = 6.283 ft .per rev. x 2000 rev. per min. = 12,566 feet per
minute
Power = 100 pounds x distance per minute
Power = 100 lb x 12,566 ft. per minute = 1,256,600 ft-lb per minute

HORSEPOWER is defined as 33000 foot-pounds of work per minute.
HP = POWER (ft-lb per min) ÷ 33,000.
HP = (1,256,600 ÷ 33,000) = 38.1 HP.
TORQUE = FORCE x RADIUS.
If we divide both sides of that equation by RADIUS, we get:
(a) FORCE = TORQUE ÷ RADIUS
Now, if DISTANCE per revolution = RADIUS x 2 x π, then
(b) DISTANCE per minute = RADIUS x 2 x π x RPM
We already know
(c) POWER = FORCE x DISTANCE per minute
So if we plug the equivalent for FORCE from equation (a) and distance per minute from
equation (b) into equation (c), we get:
POWER = (TORQUE ÷ RADIUS) x (RPM x RADIUS x 2 x π)
Dividing both sides by 33,000 to find HP,
HP = TORQUE ÷ RADIUS x RPM x RADIUS x 2 x π ÷ 33,000
By reducing, we get
HP = TORQUE x RPM x 6.28 ÷ 33,000
Since
33,000 ÷ 6.2832 = 5252
Therefore
HP = TORQUE x RPM ÷ 5252

Variable Speed Arrangements
• In most of the practical systems it is required to
operate the motor at different speed as per the
requirements
This is achieved by the implementation of Gears

Gears
• A gear or cogwheel is
a rotating machine part having cut teeth, or
in the case of a cogwheel, inserted teeth
(called cogs), which mesh with another
toothed part to transmit torque

Path determination
• Path planning for industrial robots is an
essential aspect of the overall performance of
automation systems.

• Essentially, path planning algorithms
determine how an industrial robot arm
should approach a part, how it should
process a part, and how it should orient
itself for optimal productivity and to avoid
collisions.

The Role of Proper Robot Path
Planning in Production
• Robot Accuracy: a robot’s path needs to be
meticulously planned in order for it to productively
process a part with little or no error.
• Task Repeatability: once a robot’s path is well-
defined it can repeat the same task thousands of
times without variation to help accelerate
throughput.
• Product Quality: when products are created with a
high degree of accuracy and repeatability, there are
fewer mistakes and higher consistency, leading to
higher overall quality products.

Different types of Motion
• limited sequence,
• point-to-point (PTP),
• continuous path and
• intelligent.

Limited Sequence control
• Characteristics: Each link can only stop at a
few limited positions, controlled by sensors,
mechanical stops.

point-to-point (PTP),
• Each axis or joint has many stoppable positions.
However, trajectory is not controllable at will,
although it may be roughly deterministic
– One joint at a time
• Joints can not move simultaneously. Rather, one moves after
another, in some sequence.
– Slew motion
• All joints that require motion start simultaneously at default joint
speeds
– (linear) Joint interpolation
• All joints that require movement start simultaneously and stop
simultaneously.

Continuous path Control
• Several joints can move simultaneously in
some user-specified trajectory. The most useful
ones are linear and circular interpolations.
– Linear interpolation
• Regardless of robot configuration, the robot attempts to
achieve a linear line while maintaining the tool
orientation.
– Circular interpolation
• In circular interpolation, robot will achieve a circular
motion while maintain the tool orientation.

Intelligent control
• Motions are flexible based on sensors and
intelligent to cope with various situations

Sensors
• Uses of sensors:
– Safety monitoring
– Interlocks and work cell control
– Part inspection for quality control
– Determining position and related information
about objects in robot cell

Review Questions
• Working of fiber optic sensor
• Methods of path determining
• Gearing ratio
• Types of drives and sensors
• Element of robotic vision
• Tactile sensor working
• Proximity and Range sensor working

Robotics and automation _ power sources and sensors

Recommended

More Related Content

What's hot (20)

Similar to Robotics and automation _ power sources and sensors (20)

More from JAIGANESH SEKAR (20)

Recently uploaded (20)

Robotics and automation _ power sources and sensors