BY DIPEN,

JAKSHIL, NIRMAL.

Pick And Place Mechanism

A robotic arm is a type of mechanical arm, usually programmable, with similar functions to a human arm; the arm may be the sum total of the mechanism or may be part of a more complex robot.

The links of such a manipulator are connected by joints allowing either rotational motion (such as in an articulated robot) or translational (linear) displacement.

 The links of the manipulator can be considered to form a kinematic chain. The terminus of the kinematic chain of the manipulator is called the end effectors and it is analogous to the human hand.

About pick and place mechanism

A degree of freedom is a joint on the arm, a place where it can bend or rotate or translate. We can typically identify the number of degrees of freedom by the number of actuators on the robot arm(in case of serial arms). so for simplicity it is treated as separate subsystem in basic robot arm design.

Degrees of Freedom (DOF)

The robot workspace (sometimes known as reachable space) is a collection of points that the end effector (gripper) can reach. The workspace is dependent on the DOF angle/translation limitations, the arm link lengths, the angle at which something must be picked up at, etc. The workspace is highly dependent on the robot configuration. The figure given below describes the workspace for our serial arm.

Robot Workspace (Work Volume)

Cartesian Gantry Robot Arm

Cartesian Gantry Robot Arm

To estimate the torque required at each joint, we must choose the worst case scenario

As arm is rotated clockwise, L, the perpendicular distance decreases from L3 to L1 (L1=0). Therefore the greatest torque is at L3 (F does not change) and torque is zero at L1.

Motors are subjected to the highest torque when the arm is stretched out horizontally

Robot Arm Torque

If your arm has multiple points, you must determine the torque around each joint to select the appropriate motor

Robot Arm Torque

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1. Robotic arm (gripper) to hold and release object

2. Lead screw assembly to move the arm up and down

3. Electronic circuits for the controls

It is divided mainly in three parts

Grippers

• vacuum grippers• pneumatic grippers• hydraulic grippers • servo-electric grippers• Magnetic grippers

Types of grippers

The vacuum gripper has been the standard  in manufacturing because of its high level of flexibility. This type of robot gripper uses a rubber or polyurethane suction cup to pick up items. Some vacuum grippers use a closed-cell foam rubber layer, rather than suction cups, to complete the application.

vacuum grippers

The hydraulic gripper provides the most strength and is often used for applications that require significant amounts of force. These robotic grippers generate their strength from pumps that can provide up to 2000psi. Although they are strong, hydraulic grippers are messier than other grippers due to the oil used in the pumps. They also may need more maintenance due the gripper being damaged because of the force used during the application.

hydraulic grippers

The pneumatic gripper is popular due to its compact size and light weight. It can easily be incorporated into tight spaces, which can be helpful in the manufacturing industry. Pneumatic robot grippers can either be opened or closed, earning them the nickname “bang bang” actuators, because of the noise created when the metal-on-metal gripper operates.

pneumatic grippers

The servo-electric gripper appears more and more in industrial settings, due to the fact that it is easy to control. Electronic motors control the movement of the gripper jaws. These grippers are highly flexible and allow for different material tolerances when handling parts. Servo-electric grippers are also cost effective because they are clean and have no air lines.

servo-electric grppers

ElectromagnetsPermanent magnets

Magnetic grippers

Electromagnetic grippers include a controller unit and a DC power for handling the materials. This type of grippers is easy to control, and very effective in releasing the part at the end of the operation than the permanent magnets. If the work part gripped is to be released, the polarity level is minimized by the controller unit before the electromagnet is turned off. This process will certainly help in removing the magnetism on the work parts. As a result, a best way of releasing the materials is possible in this gripper.

Electromagnets

The permanent magnets do not require any sort of external power as like the electromagnets for handling the materials. After this gripper grasps a work part, an additional device called asstripper push – off pin will be required to separate the work part from the magnet. This device is incorporated at the sides of the gripper.

The advantage of this permanent magnet gripper is that it can be used in hazardous applications like explosion-proof apparatus because of no electrical circuit. Moreover, there is no possibility of spark production as well.

Permanent magnets

In constructing the arm, we made use of five servo motors (including gripper) since our structure allows movement in all three dimensions. There is a servo motor at the base, which allows for angular movement of the whole structure; other two at the shoulder and elbow to allow the upward and downward movement of the arm; one for the movement of the wrist while the last servo motor at the end effector allows for the gripping of objects.

The serial arm is a four degree of freedom system. Three DOF control the position of the arm in the Cartesian pace, one for wrist orientation and one additional servo for actuating gripper.

MECHANICAL DESIGN

ASSEMBLY DETAILS OF ARM

What are six axis robots? Industrial robots have

various axis configurations. The vast majority of articulated robots, however, feature six axes, also called six degrees of freedom. Six axis robots allow for greater flexibility and can perform a wider variety of applications than robots with fewer axes.

What are six axis robots?

ELECTRONICS AND CONTROL

Servos are a special type of DC motors with built in gearing and feedback control loop circuitry and they don’t require motor controllers. These motors are mainly developed for making robots, toys, etc. that are mainly used for education and not for industrial applications.

Servos are becoming extremely popular with robot, RC plane, and RC boat builders. Most servo motors can rotate about 90 to 180 degrees. Some rotate through a full 360 degrees or more. However, servos are unable to continually rotate, meaning they can't be used for driving wheels (unless modified), but their precision positioning makes them ideal for robot arms and legs, rack and pinion steering, and sensor scanners to name a few. Since servos are fully self contained, the velocity and angle control loops are very easy to implement. To use a servo, we connect the black wire to ground, the red to a 4.8-6V source, and the yellow/white wire to a signal source (such as from your microcontroller). Vary the square wave pulse width from 1-2ms and the servo is now position/velocity controlled.

Servo motor

Servo Wiring:All servos have three

wires:Black or Brown is for

ground.Red is for power

(~4.8-6V).Yellow, Orange, or

White is the signal wire (3-5V).

Servo Voltage (Red and Black/Brown wires):

Servos can operate under a range of voltages. Typical operation is from 4.8V to 6V. There are a

few micro sized servos that can operate at less, and now a few Hitec servos that operate at much

more.

While the black and red wires provide power to the motor, the signal wire is what we use to command the servo. The general concept is to simply send an ordinary logic square wave to your servo at a specific wave length (50Hz), and the servo goes to a particular angle. The wavelength directly maps to servo angle. In our case Arduino Mega takes input from the PC and generates

the corresponding square wave, which in turn controls the angular position of the servo motor.

The standard time vs. angle is represented in this chart:

Signal Wire (Yellow/Orange/White wire):

Overview An Arduino is a single-board microcontroller and a

software suite for programming. It is designed for an Atmel AVR processor and features on-board I/O support. The software consists of a standard programming language and the boot loader that runs on the board.

We are using Arduino Mega microcontroller board based on the ATmega1280.

It has 54 digital input/output pins (of which 14 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button.

It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started.

BASIC CONCEPT OF ARDUINO

•POWER: The Arduino Mega can be powered via the USB connection or with an external•power supply: The power source is selected automatically.

•The power pins are as follows:•VIN: The input voltage to the Arduino board when it's using an external power source.•5V: The regulated power supply used to power the microcontroller and other components on the board.•3V3: 3.3 volt supply generated by the on-board FTDI chip. Maximum current draw is 50 mA.•GND: Ground pins.•MEMORY: The ATMEGA 1280 has 128 KB of flash memory for storing code.•COMMUNICATION: The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the Arduino board. The RX and TX LEDs on the board will flash when data is being transmitted via the FTDI chip and USB connection to the computer (but not for serial communication on pins 0 and 1. It has a number of facilities for communication with a computer, another Arduino, or other microcontrollers.

Get an Arduino board and cableIn this tutorial, we assume you're using an Arduino Mega.

The Arduino is a simple board that contains everything you need to start working with electronics and microcontroller programming. This diagram illustrates the major components of an Arduino Mega.

You also need a standard USB cable (A plug to B plug): the kind you would connect to a USBprinter, for example.

5V power supply using 7805.7805 is a 5V fixed three terminal positive voltage regulator IC. The IC has features such as safe operating area protection, thermal shut down, internal current limiting which makes the IC very rugged. Output currents up to 1A can be drawn from the IC provided that there is a proper heat sink. A 9V transformer steps down the main voltage, 1A bridge rectifies it and capacitor C1 filters it and 7805 regulates it to produce a steady 5Volt DC. The circuit schematic is given below.

Circuit diagram with Parts list.

Connection servo motors with Arduino and external power supply

Servomotors are special position motors. They are often used in RC airplanes, RC cars and robots, where a precise position is required. You can easily find them in a RC specialized store.A typical servomotor consists in a DC motor connected with a control circuit and a gear box. The gear box converts the DC motor into torque. The control circuit has a potentiometer for feedback, so it can read the current position and adjust it automatically. A servomotor can't do a complete turn, they go up to 90 or 180 degress.A servomotor has 3 wires: red (V+), black (GND) and white or yellow (SIGNAL). The red and black are the power supply wires and the third is for control. To control a servomotor, power it with 5V and supply the control wire with a voltage from 0 to V+, the position will be proportional to the Signal voltage. To test it, connect it like this: