For example,

• Assembly line of an automobile.
• An automated sugar factory.
• Printing of newspaper.

NEED OF AUTOMATION

Although the basic reason for automation is quality of product, higher production rates and an economical product but the reasons for automation vary from the manufacturing industry to industry.
Some of the reasons to justify automation are:

• Increase labour productivity.
• Reduce labour cost.
• Mitigate the effects of labour shortages.
• Reduce or eliminate routine manual and clerical tasks.
• Improve worker safety.
• Improve product quality.
• Reduce manufacturing lead time.
• Accomplish processes that cannot be done manually.
• Reduce unit cost.

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Industrial robots come in a variety of shapes and sizes and different joint motions. Depending on the joints, a robot can possess number of motions, but the basic arm and body configuration is limited by the degree of freedom. As only three degree of freedom is associated with the arm and body, the basic robot configuration in industrial robots commonly available as

• Polar configuration
• Cylindrical
• Cartesian co-ordinate
• Joint arm
• SCARA

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SCARA is an acronym for Selective Compliance Assembly Robot arm. One Scara configuration is shown in Fig. 1. In Scara, the robot arm has following movements:

1. Linear movement that allows the arm to extend and retract because of one orthogonal joint.
2. Rotary movement at the top of the column about the shoulder joint (along vertical axis) because of one revolving joint.
3. Rotary movement at the output arm about the elbow joint (along vertical axis) because of one rotational joint.

Fig. 1: SCARA configuration

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The jointed arm robot configuration resembles to a human arm. The jointed arm and body configuration is shown in Fig. 1. In this configuration, the robot arm has following movements:

1. Rotary movement (vertical column that swivels about the base) that occurs around an axis (horizontal) parallel to the base because of one twisting joint.
2. Rotary movement at the top of the column about the shoulder joint (along horizontal axis) because of one rotational joint.
3. Rotary movement at the output arm about the elbow joint (along horizontal axis) because of one rotational joint. It gets three rotary joints and three wrist axes, which form into six degrees of freedom. As a result, it has the capability ty to be controlled at any adjustments in the work space.

Fig. 1: Jointed Arm Body Configuration

Advantages of Jointed Arm Robot Configuration

The jointed arm configuration has following advantages:

• It has a huge work volume.
• It has higher flexibility and so is quick in operation.
• Two rotational joints allows for higher reach from the base.
• It provides reaching the congested small openings without restrictions.

Limitations of Jointed Arm Robot Configuration

The jointed arm configuration has following limitations:

• It has a difficult operating procedure.
• It has plenty of components.

Applications of Jointed Arm Robot Configuration

• The jointed arm configuration finds applications in spray painting, spot welding, arc welding etc.
• This configuration robot is also called an articulated robot.

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The Cartesian coordinate robot is also referred to as rectilinear robot or X-Y-Z robot of the spherical configuration because it is equipped with three sliding joints for assembling XYZ axes. The Cartesian coordinate robot arm and body configuration is shown in Fig. 1. The arm movement of a robot using the Cartesian configuration can be described by three intersecting perpendicular straight lines, referred to as the X, Y and Z axes. In the Cartesian coordinate configuration, the robot arm has following movements:

• Linear movement that allows vertical lift to the arm because of one linear joint.
• Two sliding movements those are perpendicular to each other because of two orthogonal joint.

This configuration robot will process in a rectangular workspace by means of this three joints movement. Because movement of the arm can start and stop simultaneously along all three axes, motion of the tool tip is smoother. This allows the robot to move directly to its designated point, instead of following trajectories parallel to each axis.

Fig. 1: Cartesian Robot

Advantages of Cartesian Robot Configuration

The Cartesian Robot Configuration has following advantages:

• It has high load carrying capability.
• It provides a rigid structure and also a high degree of mechanical rigidity and accuracy.
• It can produce high repeatability with least error and at a good speed.

Limitations of Cartesian Robot Configuration

The Cartesian Robot Configuration has following limitations:

• It has a small and rectangular work envelope.
• It has a reduced flexibility.

Applications of Cartesian Robot Configuration

The Cartesian co-ordinate configuration finds applications in inspection, assembly, machining operations, welding, finishing operations etc. This configuration also get a name of Gantry Robot as it is capable of carrying high loads with the help of its rigid structure and this weight lifting capacity does not vary at different locations within the work envelope.

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The cylindrical robot configuration allows the robot to reach the work space in a rotary movement like a cylinder. The cylindrical arm and body configuration is shown in Fig. 1. In the cylindrical configuration, the robot arm has following movements:

• Rotational movement of the column about its axis because of one twisting joint.
• Linear movement of the assembly along the column because of one linear joint.
• Linear movement in and out, relative to the column axis because of one orthogonal joint.

Fig. 1: Cylindrical Body Configuration

Advantages of Cylindrical Robot Configuration

The cylindrical configuration has following advantages:

• It has higher load carrying capacity.
• It provides high rigidity to the manipulator.
• It is generally suitable for pick and place applications.

Limitations of Cylindrical Robot Configuration

The cylindrical configuration has following limitations:

• It requires more floor space.
• It has a reduced mechanical rigidity because robots with a rotary axis must overcome the inertia of the object when rotating.

Applications of Cylindrical Robot Configuration

The cylindrical configuration finds applications in:

• Conveyor pallet transfers,
• Machine tool loading,
• Forging applications,
• Packing operation,
• Precision small assembly etc.

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The polar configuration is also referred to as the spherical configuration as this combination allows the robot to operate in a spherical work volume. The polar arm and body configuration is shown in Fig. 1. In the polar configuration, the robot arm has following movements:

• Linear movement that allows the arm to extend and retract because of one linear joint.
• Rotary movement that occurs around an axis (vertical) perpendicular to the base because of one twisting joint.
• Vertical lift of the arm about the pivot point because of one rotational joint.

Fig. 1: Polar Arm and Body Configuration

Advantages of Polar Robot Configuration

The polar configuration has following advantages:

• It allows long reach capability in the horizontal position.
• It provides good load lifting capabilities.
• It is suitable for applications where a small amount of vertical movement is adequate, such as loading and unloading of components.

Limitations of Polar Robot Configuration

The polar configuration has following limitations:

• It has a low vertical reach.
• It has a reduced mechanical rigidity.

Applications of Polar Configuration

The polar configuration finds applications in machine tool loading, movement of material, stacking of components, heat treatment operations forging etc.

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Fig. 1: General Structure of Robotic Mechanism

This is compared with the predefined task given to the controller. The errors between the prescribed and the actual task are then fed back into the controller, which then synthesizes the necessary corrective signals. These are in turn fed back to the actuators, which then drive the mechanical system through the required task. Thus, the given task is performed by the robot.

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Degrees of freedom (DOF) is ” a term that describes a robot’s freedom of motion in three dimensional space”. Degree of freedom for a robot is defined as “the number of independent movements performed by the robot wrist in three dimensional space, relative to the robot’s base”. It refers to the ability of the robot arm to move forward and backward, up and down and to the left and to the right. For each degree of freedom, a joint is required. A robot requires six degrees of freedom to be completely versatile. The number of degrees of freedom defines the robot’s configuration. Many robotic applications require movement in all the three directions; i.e. X, Y and Z. These tasks require three joints, or three degrees of freedom.

The three degrees of freedom in the robot arm are 1 rotational and 2 linear.

Rotational movement: The rotational movement is about a vertical axis. Because of this, the robot can swivel its amr about its base.

Radial movement: The linear movement in horizontal direction allows the extension and retraction of the arm relative to the base. This movement allows the robot arm to cover large area along radial direction.

Vertical movement: The linear movement about the vertical axis provides vertical lift to the robot arm.

These degree of freedom of robots arm are shown in Fig. 6.1 (a). For applications that require more freedom, additional degrees can be obtained from the wrist, which can be obtained from the end effector. These additional three degrees of freedom in the wrist provide rotary motion to the arm.

These degree of freedom are named as: pitch, yaw and roll as shown in the Fig. 6.1 (b).

Pitch: The pitch, or bend, is the up-and-down movement Of the wrist about the horizontal axis.

Yaw: The yaw is the side-to-side movement, or swivel about the vertical axis in horizontal plane.

Roll: The roll is the rotation or swivel about the arm axis (horizontal).

• Degrees of Freedom of Robot Arm
• Degrees of Freedom of Robot Wrist

Fig. 6.1

Thus, the first three degrees of freedom are for arm movement while the remaining are for wrist movement. A robot requires a total of degrees of freedom to locate and orient its hand at any point in its work envelope, Fig. 6.2.

Fig. 6.2; Six Degree of Freedom

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A mechanical device with joints and links, guided by sensors and driven by actuators, controlled by a program, that handle and manipulate parts, materials, tools and devices for performing different tasks in varous work conditions can be called as a robot.

ADVANTAGES OF ROBOT

Industrial robots provides the following advantages:

• Robots can carry out work at high repeatability.
• Productivity can be improved as robots being machine do not need allowances.
• They can work in unfavourable circumstances.
• The manufacturing speed can be increased and the cost be reduced when robots are used.
• Using robots may minimize the wasting of materials.
• Using robots can improve the quality of a product by its ability to assemble precise components.
• They can be used In assembly work with high precision and density.
• The program can be modified easily, so robots can increase the flexibility in manufacturing.

RESTRICTIONS OF ROBOT

• Despite the advantages in using robots, there are a ot of restrictions as well.
• The cost for setting up a robot for industrial use is very high.
• It may sometimes be difficult to identify material because of limitations in the senses of robots.
• Robots cannot do very precise or delicate task like grinding of small god jewelery, making pottery etc.
• The efficiency of robot also depends on the experience, knowledge and judgement of the programmer.
• The use of robot is not justified for production in small quantity.

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