Parts of a Robot

Robots come in many shapes and sizes. Robots consist of a number of components, that work together: the controller, the manipulator, an end effector, a power supply, and a means for programming.

Controller

The controller is the part of a robot that coordinates all movements of the mechanical system. It also receives input from the immediate environment through various sensors. The heart of the robot’s controller is generally a microprocessor linked to input/output and monitoring devices.

The commands issued by the controller activate the motion control mechanism, consisting of various controllers, amplifiers, and actuators. An actuator is a motor or valve that converts power into robot movement. This movement is initiated by a series of instructions, called a program, stored in the controller’s memory.

The controller has three levels of hierarchical control. Hierarchical control assign s levels of organization to the controllers within a robotic system. Each level sends control signals to the level below and feedback signals to the level above. The levels become more elemental as they progress toward the actuator.

Each level is dependent on the level above it for instructions.

The three levels are:

• Level I—Actuator Control. The most elementary level at which separate movements of the robot along various planes, such as the X, Y, and Z axes, are controlled.

• Level II—Path Control. The path control (intermediate) level coordinates the separate movements along the planes determined in Level I into the desired trajectory or path.

• Level III—Main Control. The primary function of this highest control level is to interpret the written instructions from the human programmer regarding the tasks required. The instructions are then combined with various environmental signals and translated by the controller into the more elementary instructions that Level II can understand.

Manipulator

The manipulator consists of segments that may be jointed and that move about, allowing the robot to do work. The manipulatoris the arm of the robot which must move materials, parts, tools, or special devices through various motions to provide useful work.

A manipulator can be identifi ed by method of control, power source, actuation of the joint s, and other factors. These factors help identify the best type of robot for the task at hand. For example, you would not use an electric robot in an environment where combustible fumes exist and a spark could cause an explosion.

The manipulator is made up of a series of segments and joints much like those found in the human arm. Joints connect two segments together and allow them to move relative to one another. The joints provide either linear (straight line) or rotary (circular) movement.

The muscles of the human body supply the driving force that moves the various body joints. Similarly, a robot uses actuators to move its arm along programmed paths and then to hold its joints rigid once the correct position is reached. There are two basic types of motion provided by actuators: linear and rotary. Linear actuators provide motion along a straight line; they extend or retract their attached loads. Rotary actuators provide rotation, moving their loads in an arc or circle. Rotary motion can be converted into linear motion using a lead screw or other mechanical means of conversion.

These types of actuators are also used outside the robot to move workpieces and provide other kinds of motion within the work envelope.

A tachometer is a device used to measure the speed of an object. In the case of robotic systems, a tachometer is used to monitor acceleration and deceleration of the manipulator’s movements.

End Effector

The end effector is the robot’s hand, or the end-of-arm tooling on the robot. It is a device attached to the wrist of the manipulator for the purpose of grasping, lifting, transporting, maneuvering, or performing operations of a robot system. The robot’s performance is a direct result of how well the end effector meet s the task requirements. The area within reach of the robot’s end effector is called its work envelope.

Power Supply

The power supply provides the energy to drive the controller and actuators. It may convert ac voltage to the dc voltage required by the robot’s internal circuits, or it may be a pump or compressor providing hydraulic or pneumatic power. The three basic types of power supplies are electrical, hydraulic, and pneumatic.

The most common energy source available, where industrial robots are used, is electricity. The second most common is compressed air, and the least common is hydraulic power. These primary sources of energy must be converted into the form and amount required by the type of robot being used. The electronic part of the control unit, and any electric drive actuator, requires electrical power. A robot containing hydraulic actuators requires the conversion of electrical power into hydraulic energy through the use of an electric, motor-driven, hydraulic pump. A robot with pneumatic actuators requires compressed air, which is usually supplied by a compressor driven by an electric motor.

What are the main components of any robot? 2. What part of robot’s controller is its heart? 3. What is stored in controller’s memory? 4. How many levels of control does any robot controller have and what is each level of control used for? 5. Why are the manipulator and the human arm similar? 6. How is the best type of robot for the task at hand identified? 7. What kind of motion do linear actuators and rotary actuators provide? 8. What are the functions of a tachometer in the case of robotic systems? 9. How is the area within reach of the robot’s end effector called? 10.What are sources of energy to drive the controller and actuators?

Means for Programming

The means for programming is used to record movements into the robot’s memory. A robot may be programmed using any of several different methods. The teach pendant, also called a teach box or handheld programmer teaches a robot the movements required to perform a useful task. The operator uses a teach pendant to move the robot through the series of points that describe its desired path. The points are recorded by the controller for later use.