Robot Hardware

From Industrial Robotics & Automation - Fanuc Teach Pendant Programming

Nearly all industrial robots are made up of the same basic components. Motors, bearings, controllers, and sensors may differ in size, interfaces, and ratings - and therefore not physically be interchangeable on any given robotic system, but for the most part they all function under the same basic principles.

FANUC Motors Selection

Motors

Motors are devices that convert electrical current into magnetic fields, and that magnetic field acts as force to turn a shaft, known as torque. This torque is balanced with rotational speed using gears, pulleys, or chains to move the robot.

Robot motors typically include encoders for tracking the robot's position and brakes to assist in maintaining position during long pauses and stopping during emergencies.

Motor Types

There are many types of motors available, but the specifics of how they work is beyond the scope of this course. The following is a list of common motors you may encounter while working in an industrial setting.


Our FANUC robot uses an AC motor with positional feedback, making it an AC servo motor. These are fairly common because they are reliable and powerful. The permanent magnets inside do add considerably to weight, but FANUC robots are designed to have their motors at a point that causes the least leverage forces on each axis. On some robots, the motor is placed at a point behind the arm driving it, allowing the motor's mass to "counterbalance" the weight of the load and further arm components.

Robots rarely work on their own, integrating into operational cells that include electromechanical systems such as conveyors powered by motors. These may be controlled directly by the robot controller as an additional axis, or external devices such as VFDs, PLCs, and relay logic.

Brakes

The brakes on the robot are mechanical and are active in the deenergized state (a spring applies force). To deactivate them, the robot controller sends a signal to apply 90V DC to an electromechanism. The robot's axis motors are powered to hold the arm in position before the brakes are disengaged, to automatically apply brakes in the event of power loss, and to apply the brakes when an emergency stop is triggered.

The motors themselves are also used as braking mechanisms. Force is applied in the opposite direction of any unintentional acceleration that is detected. Acceleration may be caused by the force of gravity, a load that shifts or sways, or motion of the tool. Some of these conditions can be modeled in software such as RoboGuide, allowing the robot to compensate preemptively, reducing wear, time, and energy consumption.

Pulse Coders

The pulse coders are not absolute - they track changes in position, but have no "reference" position built into them. A robot installer must define a location to be considered "zero". All positions are then calculated as being relative to whatever the operator set as zero.


The pulse coders send data to a microcontroller (a small, efficient computer) that tells it how much the joint moves in real time, and the microcontroller relays this to the robot's controller. The microcontroller is used so that if the robot moves at all while the controller is not powered, position can still be tracked. The microcontroller consumes so little power that it can run from batteries that are installed in the base of the robot.

It is easiest to think of this system in the same manner as we keep time in our households. During a power outage, your home appliances lose track of time. When power is restored, you can then recalibrate them, setting the correct time. Your cell phone, watch, or battery clocks are completely unaffected by a loss of household power, so you read the correct time from one of them, and set it on your microwave. The same process occurs automatically whenever a robot's controller is powered on.


Absolute Vs. Relative

You learned about absolute and relative measurements in your Pneumatics and Hydraulics course. Absolute pressure is a reading that starts at absolute zero, a perfect vacuum. Most gauges use relative pressure, which defines zero as the current atmospheric level, meaning it reads how much pressure is in the vessel or line relative to what is outside the line. Since the outside pressure is constantly changing due to weather and even the HVAC systems in the building, when reading a simple relative gauge it is common practice to define the "relative" zero pressure as equal to 14.7 PSI on the absolute scale.

Robots are designed to work at extreme precisions, and therefore cannot rely on an assumed figure or for the zero position. Without building expensive absolute position sensors into each of the robot's motors, they rely on continually tracking changes relative to the initial zero position.


When a robot is first put in service, it is calibrated with expensive measuring devices. They place the robot into a precise known position and configuration and then issue a command in the software to let it know "this is the zero position". If a robot loses power and the batteries die, the robot will need to be recalibrated in what is known as a Mastering Procedure. Mastering a robot's positional tracking is outside the scope of this course, but is well documented in the associated manuals and can be performed by someone who has completed this course.

Teach Pendant

Adhering to good practices will make programming the robots quicker, diagnostics easier, and allow others to understand your programs better.

The teach pendant is the main interface we use for writing programs. We use the FANUC iPendant with touchscreen color display. For information on use of the teach pendant and details on buttons and menus, see Teach Pendant.

The buttons on the teach pendant are a membrane keypad and are laid out uniformly across different FANUC robots. The ROBOGUIDE software includes a digital version of the teach pendant, with matching keys and display.

At the top of the membrane keypad are five F-keys known as "soft keys" which functions change depending on what is currently displayed on the screen. The rest of the keys are fixed functions that do not change.


Below the soft keys are the navigation keys. From left to right:

  • MENU - The Menu button opens an on screen menu allowing you to reach nearly all screens available on the teach pendant.
  • SELECT - The select button opens a list of existing programs. From this screen you can create a new program as well.
  • EDIT - Edit takes you to the last open program. Use this key whenever you need to get back to your program.
  • DATA - Data opens up the screen for viewing and editing data registers.
  • FUNCTION - Function is a menu of options relating to the teach pendant and controller states.
    • Abort All - This command tells the controller to end all programs, allowing you to begin another or analyze data from that time.



Controller

FANUC r30ib Controller

The controller is the box connected to each robot containing all the smart and power technology. Each robot has a list of compatible controllers, which can be referenced on FANUC's product pages. While custom controllers exist, the most common are A, B, and Mate variants. The bigger controllers can hold more equipment, from PLCs to extra motor amplifiers, communications equipment to relay boards.The smaller controllers can more easily be made mobile, or are good for integrating into robot cell cage walls.

The controller holds all the necessary technology to handle power, such as the following:

  • Circuit Breaker
    • The "RED" area of the circuit breaker switch is the ON condition.
    • The "GREEN" area of the circuit breaker switch is the OFF condition.
    • Turning the breaker switch counter clockwise past the OFF condition will open the panel.
    • A locking tab is available on the circuit breaker, allowing lock-out tag-out to be implemented during repair.
  • Emergency Stop Button
  • Power Supply
    • The robot takes in AC mains voltages (120, 240, 208, 480, etc) but the computer components require DC voltages. The power supply efficiently converts AC to DC at many voltages.
  • Servo Amplifier
    • The servo amplifier takes the signals from the processor and brings it up to a high voltage, low impedance level suitable for the motors.
      • You can think of the servo amplifier acting the same as an audio amplifier. Your cell phone's headphone port can't power massive speakers, but it can provide signal to a stereo amp that connects to massive speakers. In fact, the underlying design of the most common servo amplifiers are identical to the most common audio amplifier type, Class-D. You could theoretically drive some AC servos with a surround sound amplifier, although it would not last very long.
    • Depending on the robot company you elect to use, the servo amplifiers may be built into the arm itself, letting low voltage signal control each motor. Other designs place the amplifiers into the controller's box, allowing it to stay cool using the same fans as the rest of the electronics.
FANUC Modules within a controller.
  • Main Board
    • The main board contains the "computer" that handles all the software features. It communicates with the robot, the teach pendant, the amplifiers, and the external devices.
  • Standard Operator Panel (SOP)
    • The standard operator panel contains the most basic inputs and outputs for operational use. These are the buttons and lights that an unqualified technician may be tasked to interact with:
  • Programmable Logic Controllers
    • PLCs are often integrated into robot controllers, or connected externally to function as simple I/O, or to communicate information between the robot and other systems that may not be designed to communicate with robots.
      • Allen Bradley
      • Siemens
  • Communications Interfaces
    • Robots contain a selection of interfaces for data transfer. Much as your standard computer will have a variety of ports to connect to different peripherals, robots will have a variety of options available for connecting to other industrial systems.
      • Modbus
        • RTU - RTU is the old standard but is still very common. It is a communications standard that runs on RS-232 and RS-485.
        • TCP/IP - With the emergence of cheap gigabit ethernet devices, Modbus is commonly being run across IP networks, using the same protocols and standards as internet networks.
          • As a note, Modbus RTU to Modbus TCP/IP converters exist and are an option to keep using old, fully functional RTU equipment operating on the floor while being able to communicate with newly purchased equipment.
          • TCP/IP networks often include a server running concurrently for logging and efficiency analysis.
      • Ethernet TCP/IP
      • PROFINET
      • DeviceNet


Operator Panel

Operator Panel

The Standard Operator Panel on the FANUC robots is typically the front door to the robot controller. While specific units include different devices, the most common indicators, buttons, and switches are the following:

  • Outputs
    • Fault Indicator
    • Battery Alarm
    • Remote Indicator
  • Inputs
    • Breaker Switch
      • The breaker switch is usually the main power control for the robot.
        • The green position is the "safe" position in that the robot is unpowered.
        • The red position is the "caution" position when the robot is powered.
        • Turning past the green position will open the door.
        • As long as the robot is plugged in, dangerous voltages will be available at the breaker module. Always completely unplug the controller before working near or on the breaker module.
      • A lockout/tagout hole is available in the switch handle. Turn to a safe condition and pull out the metal tab, revealing the hole.
      • Mains voltage is still available at the breaker switch even when in the off condition. Take precautions when working around the breaker.
    • On & Off Buttons
      • On some units, the breaker will provide power but not directly start up the robot controller. Push the ON button to begin this process. The breaker may power internal PLCs, communication devices, or I/O devices separately from the ON/OFF buttons.
    • Mode Select (Auto/T1/T2 Key)
      • Auto mode is the controller's production operation.
      • T1/T2 are modes specifically configured for testing and programming, with different safety and configuration settings.
    • Cycle Start Button
      • When in local mode, with the mode select in the AUTO position, the Cycle Start Button will run the currently selected program.
        • In our lab, running in AUTO mode requires everyone to stand at a safe distance. Starting with the green Cycle Start button, ensure your program is designed in a way that will let you leave the safety sensor's range before beginning motion.A remote IO box is a valid method of doing so, with the program containing a WAIT statement tied to a box switch.
    • Emergency Stop
      • Push the E-Stop button in to enable a fault, pull out to return to a running state. Always be aware of the location of the emergency stop buttons for all nearby machines.
    • User 1 & User 2
    • Fault Reset
      • In our lab, we reset faults using the teach pendant, but on many units this can be accomplished with the Fault Reset button (blue).


FANUC robots support custom standard operator panels. These often include buttons for running macros, modifying data, or selecting program options.


HMI

HMI


An HMI is the Human-Machine-Interface commonly seen on industrial machines. This does not include the programming UI we use on the teach pendant, but the teach pendant is capable of serving as an HMI.

As robot programmers, we may be tasked with creating an HMI that allows operators and technicians to access certain programs and data without risking accidental changes that may affect the operation of a machine. This may include startup/shut down processes, calibration, product changes, cleaning, maintenance procedures, and even random quality testing.


Robot Types

If you asked a dozen random people on the street to draw a robot, you'd likely get a dozen completely different types. Our lab uses the LRMate 200id 4s which is a 6-axis Articulated robot arm. The human arm is also articulated and can be compared to a six axis robot. Six axis is especially useful, as an object can be picked up and placed into a new position at any orientation. In comparison, a common fused-filament 3D printer is a 3-axis robot, able to move X (forward-back), Y (left-right), and Z (up-down) directions, but has no ability to rotate the part or tool.

Other types include, but are not limited to:

  • Cartesian - A cartesian robot may not strike you as even being a robot at first because of its simplicity. Linear rails/actuators move a tool independently in each axis. 3 dimensions would be 3 linear motion devices. One axis is responsible for X motion, which may or may not be "riding on" another axis responsible for Y motion, and so forth. 3D printers are often Cartesian, as well as paper printers you may have at home.
    • Simple design - Linear motion is easy to understand, create, and control.
    • Powerful in low axis numbers
    • Easily upgraded, modified, fixed - An axis may be extended, its motor upgraded, or the drive system (belts, gears, pulleys) overhauled without affecting other axes. This is common for 3d printers, as the length of each axis limits the maximum size of the parts they may create. Doubling the size of an axis of a 3D printer may cost less than 10% of the printers original price and effectively double the size of parts that can be printed.
    • No orientation motion
  • SCARA - Two parallel joints offset by an arm. Very quick, accurate, and cost effective. These robots usually only handle 3 dimensions, and can be simplified at 2.5 (up/down) for applications such as laser engraving or contact testing.
    • Pick and place for electronics assembly.
    • Drilling for small products.
    • Sorting and packaging.
    • Limited reach - the robot's advantages work best only at short arm lengths. Product is typically brought into the robot's reach by conveyors or other robots.
  • Delta - Very lean robots with a gantry and 6 or more arms (or 3 rigid arms) that work based on the height of each arm. The name comes from the change in position of a triangular point.
    • Very fast - In other designs, an axis is often stacked on top of another, forcing the system to not only carry the weight of the part and tool but also the motors and joints above it. In a delta design, each motor is directly coupled to the gantry, a rigid plate that holds the tool. This allows for very high speeds and accelerations without the need for expensive light-weight motors and joints.
    • Low volume at the end of arm. Motors are in the base which is often mounted on a ceiling. Everything below the gantry is reachable and there is no risk of crashing into other joints.
    • Only capable of 3 axis motion. Adding yaw pitch or roll would be part of the tooling itself.
  • Polar - A spherical work area, polar robots work based on the angle from a central position. They may have a cartesian axis attached, allowing for motion towards or away from the central position.
    • Extremely simple - The rotation of the base accounts for the primary motion, allowing motors to be used without size or weight considerations.
    • Good for applications that don't care about rotation around the Z-axis - Pick up an object, turn your whole body around without moving your arm in any way, and set the object down. You've just moved the object, but it is now rotated as well. Polar robots are best used for tools that don't care about being rotated, such as lasers, drills, etching tools, routers, and rejection removal.
  • Cylindrical
  • Bowden


https://www.robots.com/faq/what-are-the-main-types-of-robots

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