FUNDAMENTALS OF ROBOTICS��Module 3���- Dr. Adithya Hegde�Assistant Professor�Department of Robotics and AI, MITE, Moodabidre

About the course – Module 3

Module 3 – Robot End Effector & Sensors (9 Hrs.)

• Types of End effectors
• Mechanical Grippers, Types of Grippers Mechanisms, Other types of grippers
• Tools and End effectors
• The Robot/End effector interface: Gripper selection and design
• Transducers and sensors in robotics: tactile, proximity and range sensors, uses of sensors in robotics

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ROBOT DRIVE SYSTEMS AND END EFFECTORS

• Pneumatic Drives-Hydraulic Drives-Mechanical Drives-Electrical Drives-D.C. Servo Motors, Stepper Motors, A.C. Servo Motors-Salient Features, Applications and Comparison of all these Drives, End Effectors-Grippers-Mechanical Grippers, Pneumatic and Hydraulic- Grippers, Magnetic Grippers, Vacuum Grippers; Two Fingered and Three Fingered Grippers; Internal Grippers and External Grippers; Selection and Design Considerations. �

End Effectors

• Robot end effector is a device attached to the wrist of a manipulator for the purpose of holding materials, parts, tools to perform a specific task.

Examples

• Grippers
• Tools
• End of arm tooling
• Welding equipment

Classification of End of arm tooling

• According to method used to hold part in the gripper
• According to special purpose process tools incorporated in final gripper design
• According to multiple function capability of gripper

According to method used to hold part in the gripper

• Mechanical pressure gripper- Friction (or) physical configuration of the gripper retains the object
• Vacuum Gripper- This gripper are used for flat object
• Magnetic devices- These devices are used for ferrous object

According to special purpose process tools incorporated in final gripper design

• Drills
• Grinders
• Polisher
• Paint sprayers
• Welding guns and torches

According to multiple function capability of gripper

Special purpose grippers

• These grippers may be specialized device like remote centre compliance (RCC) to insert an external mating component into internal member, viz inserting a plug into hole.

Gripper

• Grippers are the end effectors used for grasping the object during work cycle. A gripper is a device which enables the holding of an object to be manipulated. Gripper just like a hand. It enables holding, tightening, handling, releasing of an object.

Examples

• Vacuum grippers
• Magnetized gripper
• Adhesive grippers

Requirements of an effective gripper

• Parts (or) items must be grasped and held without damage
• Parts must be positioned firmly (or) rigidly while being operated on
• Hands (or) grippers must accommodate parts of differing sizes (or) even of varying sizes
• Self aligning jaws are required to ensure that the load stays centred in the jaws
• Gripping (or) end effectors must not damage the part being handed
• Jaws (or) Grippers must make contact at a minimum of two pints to ensure that the part does not rotate while being positioned

Application of grippers

• Material handling
• Palletizing and depalletizing
• Arranging parts on to pallets
• Machine loading and unloading
• Picking and placing of parts on conveyor

Mechanical Grippers

• Mechanical gripper is used as an end effector in a robot for grasping the objects with its mechanically operated fingers. In industries two fingers are enough for holding purpose. Mechanical grippers act as a robot hand. A basic robot hand will have only two (or) three fingers.

Features of Mechanical Grippers

• Simple to use
• Grip using pivoting, linear (or) translation movement
• Pneumatic control is cost effective and simple to maintain
• Servo controls can be used where precise controlled gripper movement is required

Advantages of Mechanical Grippers

• Palletizing
• Rotating objects
• Moving small objects
• Moving non uniformly shaped objects
• No need for compressed air (or) other supplementary materials

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Gripper Jaw

Two (or) Dual jaw gripper

• Two jaw gripper consists of two gripping jaws that apply pressure externally (or) internally of the object. It depending on the jaw defines.

Examples

• Angular gripper
• Parallel gripper
• Toggle gripper

Three jaw Gripper

The three jaw gripper consists with three gripping jaw and apply pressure like two jaw grippers.

Flexible Grippers

Flexible grippers consist with several linkage on each finger and two (or) several fingers

Multiple jaw Grippers

If more than three jaws are used to hold the object, which is called as multiple jaw grippers

Three jaw Gripper

Finger Grippers

• As like as a jaw the fingers are used to hold (or) grasping the object is called finger grippers.

Single finger gripper

• Only one gripping fingers is mounted on the wrist for holding the objects is called single finger gripper.

Two (or) dual finger gripper

• Two fingers are mounted on the wrist for holding the objects are called two finger (or) dual fingers

Types of two finger gripper

• Parallel gripper
• Angular gripper
• Toggle gripper

Single finger gripper

Two (or) dual finger gripper�

1. Parallel gripper

2. Angular gripper�

3. Toggle gripper�

Three finger gripper�

• If three fingers are attached on wrist for holding the object is called three finger gripper.

Multiple finger gripper

• If two (or) three fingers are not enough for holding work, more than three finger grippers are designed for reliable and precise palletizing (or) depalletizing and positioning of work pieces in assembly and production process.

Based on Hold the object

Internal gripper

• In internal gripper, the finger pads are mounted on the inside of the fingers. This mounting allows the pads to fit into the inside diameter of the part it must lift. The pads are pressed against the inside wall of the part

Internal gripper

External Gripper

• An external gripper is designed so that the finger pads press against the outside of the component. Grips the exterior surface of the object with closed finger.

External Gripper

Single mechanical device

• 1.Hook Grippers 2. Scoop Grippers

• 1.Hook Grippers 2. Scoop Grippers

Mechanical gripper based on contact

1. Unilateral gripper

Only one point (or) surface is touching (or) contact the object to be handled is called unilateral gripper.

Example

i) Vacuum pad gripper

ii) Electro magnetic gripper

2. Multilateral Gripper

More than two points (or) surfaces touching (or) contact the components to be handled is called as multilateral gripper

Multilateral Gripper

Vacuum Grippers

• Vacuum grippers are used in the robots for grasping the non ferrous objects. It uses vacuum cups as the gripping device. Vacuum gripper is also commonly known as suction cups.
• Vacuum grippers are those which are suction cups for handling certain types of objects. This type of grippers will provide good handling if the objects are smooth flat and clean. It has only one surface for gripping the object.

Vacuum gripper specification

1. Size of suction cups

2. Supporting requirements

3. pressures requires

4. Gripping force

Suction Cups

Different devices are used in the suction cups for creating the vacuum.

1. Venturi 2. Vacuum Pump

1. Universal suction cups

• The universal suction cups are used for flat (or) slightly arched surfaces

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2. Flat suction cups

• With bars are suitable for flat (or) flexible items that need assistance when lifted.

3. Suction cups with bellows

• Suction cups with bellows are usually used for curved surfaces.
• It is used for example when separation is needed (or) when a smaller item is being gripped and needs a shorter movement.

4. Depth suction cups

• The depth suction cup can be used for surfaces that are very irregular and curved (or) when an item needs to be lifted over an edge.

Working of Vacuum Gripper (or) Suction Gripper

Vacuum Cup

Venturi type Vacuum gripper

• Venturi principles are used in the suction cups for creating vacuum
• It consist of 1. Nozzle 2. Venture jet 3. Compressor

Magnetic Gripper

• Making use of the principle of magnetism these grippers are used for holding ferrous work part. A gripper in which work piece is held by magnetic force. Magnetic has developed a magnetic gripper (or) robot end of arm tooling. A magnetic gripper is one which uses a permanent magnet for handling ferrous materials.

Magnetic Gripper

Electro magnetic Grippers

• In electro magnetic grippers require any sort of external power for handling the material. Gripper using electro magnets are generally powered by dc power for handling materials.

Electro magnetic Grippers

Permanent magnetic Grippers

• In permanent magnetic grippers do not require any sort of external powered by DC power for handling the materials. The holding grippers permanently possess high magnetic properties. They do not lose their magnetic force.

Permanent magnetic Grippers

Adhesive Gripper

• Grippers in which an adhesive substance performs the grasping action for handling fabrics and other light weight materials are called adhesive gripper.

Hydraulic gripper

• A gripper in which the work piece is hold by hydraulic force. A hydraulic gripper is used as end effector in a robot for grasping the object with its hydraulically actuated fingers.

Elements of the hydraulic gripper

• 1. Reservoir
• 2.pump
• 3. Prime mover
• 4. Actuator
• 5. hydraulic piping Force = pressure x surface
• 6. Valves

Hydraulic gripper

Hydraulic gripper

Pneumatic Gripper

• A gripper in which the work piece is hold by pneumatic force. A pneumatic gripper is used as end effector in a robot for grasping the object with its pneumatically operated fingers.

Elements of the pneumatic system

• 1. Air filter
• 2. compressor
• 3. Air cooler
• 4. Drier
• 5. Control Valve
• 6. Air Actuator
• 7. Electric motor
• 8. Receiver tank

Pneumatic Gripper

Gripper Mechanism�

• Gripper mechanism consists of finger (or) hand plates, membrane, roller suction, Vacuum, magnetism, adhesive, scoops and hooks, linkages, screws, cam, spring, string, hydraulics , rope and pulley

Linkage actuation gripper mechanism

• Linkage actuation gripper mechanism is no cam, screw and gear. There is movement only because of links attached to input and output.
• There must be perfect design of mechanism such that input actuator motion is transformed into the gripping action at the output.

CAM actuated gripper mechanism

• A cam actuated gripper with spring loaded follower can be used to provide open and close actions of fingers.
• The spring function is to force the gripper to close if the cam is moved in open direction, while the movement of cam on the other direction causes the gripper to open

Screw driven (or) actuated gripper mechanism

• The screw type actuated gripper consists of a screw connected with a threaded block. Screw driven grippers operated by turning screw. In turn giving motion to connecting links output.

Rope and Pulley driven gripper mechanism

• Rope and pulley gripper mechanism consists of a rope connected with pulley. If the pulley is rotated on revolving motion, the rope is transfer along with the direction the motion

Gear and Rack actuation system

• It consist of gear, rack and guide rail. Gear and rack mechanisms are used to convert rotation motion into linear motion.

Gripper with a rotary actuator

Translation Gripper Mechanisms

• Translational mechanisms are widely used in grippers of industrial robots. The finger motion corresponds to the piston movement without any connecting mechanisms between them.

Types of tools

• 1. Machine tool
• 2. Measuring instrument
• 3. Welding torches
• 4. Spray painting gun
• 5. Assembly tool

Wrist interface

• Wrist interface refers to those connections of one system that are matched to another system that is distinctly different because of the basic nature of each system

Wrist Assembly

• A wrist consisting of two (or) three compact joints attached to the wrist is a gripper to grasp a work part (or) a tool to perform process

Gripper force analysis�

• Gripping force is the maximum effort applicable by the end effector.

Design of Gripper

When designing a gripper there are a number of factors that may need consideration.

• Gripping Force
• Weight
• Supply of service
• Environmental capabilities
• Sensor capabilities
• Others

Selection of gripper

Robot and Robot sensor

Robot

A robot is a machine-especially one programmable by a computer-capable of carrying out a complex series of actions automatically

Robotic Sensor:

A device that can detect physical signal and convert into electrical signal. Robotic sensors are used to estimate a robot's condition and environment. These signals are passed to a controller to enable appropriate behavior.

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Types of robotic sensor

• Light sensors.
• Sound Sensor.
• Temperature Sensor.
• Contact Sensor.
• Proximity Sensor.
• Distance Sensor.

• Pressure Sensors. ...
• Tilt Sensors.
• Voltage sensor
• Current sensor
• IMU Sensor
• Acceleration sensor.

Light sensors

A Light sensor is used to detect light and create a voltage difference. The two main light sensors generally used in robots are photo resistor and Photovoltaic cells.

TYPES OF LIGHT SENSOR

• VEX light sensor
• LEGO light sensor
• Light Sensor 1000 lux
• SCI-BOX Light Detector
• TAOS TSL235R Light to Frequency Converter
• Parallax QTI Sensor
• DFRobot Ambient Light Sensor
• Arduino LilyPad light sensor
• DFRobot BH1750 light sensor
•  CdS photoconductive cell

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 VEX light sensor:

The light sensor from VEX is one of the simplest light sensors which can be used in robotics to allow a robot to detect the light

LEGO light sensor:

The LEGO light sensor is designed to fit perfectly into a LEGO robot. It can be used to improve the robot vision and is perfect for light detection, light intensity and to distinguish between a light or dark environment

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 Light Sensor 1000 lux:

The light sensor from Phidgets can measure the visible light spectrum of the human eye between 1 to 1000 lux. Output signal is analog, has a current consumption of 2 mA and an error of 5%

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SCI-BOX Light Detector:

SCI-BOX light detector is used to detect ambient light density. SCI-BOX has two different voltage outputs and works with a photoresistor.

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TAOS TSL235R Light to Frequency Converter:

The TSL235R from TAOS is a sensor that measures light intensity and its output is frequency. It can communicate with a microcontroller or other logic circuitry.

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 Parallax QTI Sensor:

 The output signal can be both analog and digital. This sensor can be successfully used in robots to follow a line or for navigation.

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DFRobot Ambient Light Sensor:

Ambient light sensor from DFRobot has an analog output value between 0 to 5 Vdc directly proportional to light intensity

Arduino LilyPad light sensor:

Arduino LilyPad is a sensor specifically designed for use with Arduino Lilypad mainboard and can be emulated perfectly on any project in robotics.

DFRobot BH1750 light sensor:

BH1750 is one of the best performing light sensors with a high resolution of 1 to 65535 lux. Works equally well in low light and in sunlight.

CdS photoconductive cell:

The photoconductive cellis a basic electronic component, both small and simple, that can be integrated into a variety of applications

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SOUND SENSOR

This sensor (generally a microphone) detects sound and returns a voltage proportional to the sound level. A simple robot can be designed to navigate based on the sound it receives. Imagine a robot which turns right for one clap and turns left for two claps. Complex robots can use the same microphone for speech and voice recognition.

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Temperature Sensor

What if your robot has to work in a desert and transmit ambient temperature?  Simple solution is to use a temperature sensor. Tiny temperature sensor ICs provide voltage difference for a change in temperature. Few generally used temperature sensor IC’s are LM34, LM35, TMP35, TMP36, and TMP37.

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Contact sensor

Contact sensors are those which require physical contact against other objects to trigger. A push button switch, limit switch or tactile bumper switch are all examples of contact sensors

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Pressure Sensors�

Pressure sensor measures pressure. Tactile pressure sensors are useful in robotics as they are sensitive to touch, force and pressure. If you design a robot hand and need to measure the amount of grip and pressure required to hold an object, then this is what you would want to use.

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Tilt Sensor�

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Tilt sensors measure tilt of an object. In a typical analog tilt sensor, a small amount of mercury is suspended in a glass bulb. When mercury flows towards one end, it closes a switch which suggests a tilt

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Distance Sensor

Most proximity sensors can also be used as distance sensors.

Type of distance sensor:

• Ultrasonic Distance Sensors
• Infrared Distance sensor
• Laser range Sensor
• Encoders
• Stereo Camera

Voltage Sensors�

Voltage sensors typically convert lower voltages to higher voltages, or vice versa. One example is a general Operational-Amplifier (Op-Amp) which accepts a low voltage, amplifies it, and generates a higher voltage output. Few voltage sensors are used to find the potential difference between two ends .Even a simple LED can act as a voltage sensor which can detect a voltage difference and light up. (not considering current requirements here)

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Current Sensors�

Current sensors are electronic circuits which monitor the current flow in a circuit and output either a proportional voltage or a current. Most current sensors output an analog voltage between 0V to 5V which can be processed further using a microcontroller.

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IMU�

Inertial Measurement Units combine properties of two or more sensors such as Accelerometer, Gyro, Magnetometer, etc, to measure orientation, velocity and gravitational forces.

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Acceleration Sensor�

An accelerometer is a device which measures acceleration and tilt. There are two kinds of forces which can affect an accelerometer: Static force and Dynamic Force

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Types of Acceleration Sensor

Static Force: Static force is the frictional force between any two objects. For example earth’s gravitational force is static which pulls an object towards it. Measuring this gravitational force can tell you how much your robot is tilting

Dynamic force: Dynamic force is the amount of acceleration required to move an object. Measuring this dynamic force using an accelerometer tells you the velocity/speed at which your robot is moving

Difference Between Digital and analogue sensor

Digital sensor

A digital sensor can only have two values: 1 or 0, all or nothing. An example of a digital sensor is a button, which can either have the value of 1 when pressed or 0 when not pressed. On a ZUM board or a similar one, the digital sensors will be connected on the digital pins D0-D13.

Analogue sensor

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An analogue sensor can have multiple states and is able to transform the quantity of light, temperature or other physical elements into a value between 0 and 1023.

Basic Transducer

Transducer�

A device which converts one form of energy to another.

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• Sensor = input to a system
• Actuator = output from a system

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What is the use of sensors?

Sensors are used to measure physical quantities such as temperature, light, pressure, sound, and humidity. They send signals to the processor. For example: A security alarm system may have an infrared sensor which sends a signal when the beam is broken.

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7 Types of Industrial Robot Sensors�

• 2D Vision
• 3D Vision
• Force Torque Sensor
• Collision Detection Sensor
• Safety Sensors
• Part Detection Sensors
• Others

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End of Module 3

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