Industrial Robots: Components, Operation, and Programming

Posted on Dec 12, 2024 in Technology

Industrial Robots

An industrial robot is defined as an automatically reprogrammable, multifunctional material handler with three or more axes. It can be positioned and used to orient material, parts, tools, or special devices to perform work in various stages of industrial production, either in a fixed position or while moving. (IFR, ISO / TR 83,737, 1988)

Degrees of Freedom (DOF)

Each of the independent movements that each joint can make with respect to the previous one.

  • 3 DOF – is the minimum (as defined by ‘robot’)
  • 6 DOF – is the maximum (for positioning and orienting)
  • 7+ DOF – redundancy

Redundancy

Increase Redundancy: No DOF for greater maneuverability and increased scope.

Actuators

Actuators generate the movement of the robot’s elements according to the orders given by the control unit. The actuators used in robotics can use pneumatic, hydraulic, or electric power.

Reducers

Increase torque: Tout = n Tin · win / wout. Greater accuracy in measuring the rotation of the shaft without introducing rides

Types of Reducers

  • Planetary
    • +: Low cost, wide range, high torque transmission
    • -: High inertia, great weight, large gaps
  • Cyclo
    • +: Medium inertia, small weight, medium gaps
    • -: Average cost, low-torque transmission
  • Harmonic Drive (HD)
    • +: Low inertia, small weight, small gaps
    • -: High cost, not overly high torque transmission

Cyclo Gearbox

A cyclo gearbox is based on the cycloidal motion of a disk driven by an eccentric curve that is integral with the input shaft. For every revolution of the eccentric, the disk moves a projection curve on the rollers of the rolling field. This development, in turn, drags the output shaft bolts. The reduction ratio is determined by the number of projections.

Harmonic Drive Reducer

A harmonic drive reducer is based on a rigid outer crown with internal teeth (circular spline) and a flexible glass (flexspline) that meshes with external teeth on the circular spline. Inside the vessel rotates an ellipsoidal bearing (wave generator) that deforms the glass, connecting the outer crown glass area corresponding to the maximum diameter of the ellipse. Having a difference of teeth Z = Nc-Nf, after a turn of the wave generator, the flexible spline teeth only move Z. Value for Z / Nf.

Charge Transfer Systems

Charge transfer systems channel the transfer of the motors to move the moving parts of the robot. They consist of two parts: the reducing system and the transmission system. Reducers decrease the fast rotation of the engine’s axes to increase torque.

Problem: To transmit the motions from the actuators to the joints to reduce the inertia.

Objective: To reduce the static torque and moments of inertia (especially at the end).

Method: Move as much weight as possible near the base of the robot.

Additional function: Convert circular motion into linear or vice versa.

Specifications: Reduced size and weight, small gaps and clearances, high performance, low friction, low wear, “maintenance-free”, able to withstand continuous operation at high torque.

Sensors

  • Presence: Detects the presence of an object with or without contact within a radius of action. Inductive sensors determine the presence or count the number of metal objects without contact. Similarly, capacitive sensors are used; however, they are larger. Finally, Hall effect sensors are used to detect ferromagnetic objects, while optical sensors are used for the reflection of a light beam reflected from an object.

Inductive, Capacitive, Hall Effect, Reed Cell, Optical, Ultrasound, Contact

  • Position: To control angular position, encoders and resolvers are used. Potentiometers are available as benefits but are not used except on rare occasions (educational robots, minor axis).

Encoders: Consist of a transparent disc with a series of opaque markings placed radially and equidistant from each other, a lighting system (LED emitter), and a photo-receiving element. The axis whose position is to be measured is coupled to the transparent disk. They provide digital information.

Analog: Potentiometer, Resolve, Synchro, Inductosyn, LVDT

Digital: Absolute encoder, optical incremental encoder, ruler

  • Speed: Relates the translational speed or voltage through.

Tacogenerator

DH Parameters

  • Number the links from 0 to N. Link 0 will be the fixed base of the robot.
  • Number the joints from 1 to N.
  • Determine the axes of each joint, rotation, or translation.
  • From 0 to N-1, put the zi axis on the axis of joint i +1.
  • Place the origin of S0 (Base System) anywhere on the z0 axis. Choose x0 and y0 with the right-hand rule.
  • From 1 to N-1, put the system at the intersection of zi with the common normal line zi-1 and zi.
  • Place xi on the common normal line zi-1 and zi.
  • Put yi to complete the right-handed system with xi and zi.
  • Place the Sn system at the end of the robot, with zn parallel to zn-1 and xn normal to zn and zn-1.
  • Get the θi turn around zi-1 so that xi and xi-1 are parallel.
  • Get the movement along di and zi-1 so that xi and xi-1 are aligned.
  • Get the movement along ai and xi to match the origin of Si-1 and Si.
  • Obtain the αi turn around xi for systems to match Si and Si-1.

Singular Configurations

Definition of physical activity: A robot’s singular configurations are those for which extreme speeds cannot be performed by finite velocity joints, or when some degree of freedom in movement is lost.

Mathematical Definition: The robot is in a singular configuration when the rank of the Jacobian matrix [mxn] is less than m. In the case that n = m, a singularity exists when the determinant of the Jacobian matrix is null (det J (q) = 0).

In practical terms: When the robot is within the limits of its workspace because it loses opportunities, they are aligned movement, or when two or more axes of joints are in the same type (rotation or translation).

Trajectory Types

  • Point to Point: The path of the end of the robot does not matter. Only matters that it reaches the indicated endpoint.

Types:

  • Movement axis to axis: Only one axis moves at a time (increased cycle time) (Only in very simple robots or those with a limited control unit).
  • Simultaneous movement of axes: The axes begin at once. Each one ends when it can (high, useless demands).
  • Coordinated movement: Start and end at the same time.
  • Coordinated and Isochrones: The path of the end of the robot does not matter, but the axes are moved simultaneously, slowing down the faster joints so that all axes are completed in time. Total time = minimum. Avoiding unnecessary requirements of speed and acceleration.
  • Continuous: The intention is that the end of the robot describes a specific and known trajectory. The path is important since during it, part of the robot performs its task (welding, laser cutting, etc.). Typical trajectories include straight lines, arcs, and others.

Methods of Programming Robots

  • Programming by Guidance: The robot is taken along the path that it will later repeat in automatic mode.
  • Passive: The programmer provides the energy to move.
  • Direct: Moves the end of the robot directly.
  • Dummy: Instead of the real robot, a dummy with the same kinematics but much lighter and easier to move is used.
  • Active: Uses the proper operation of the robot system, controlled from a keypad or joystick.
  • Textual Programming: Based on the existence of a formal programming language to indicate the commands to the robot. PROGRAM: A sequence of commands edited and written by the user and then executed by the robot.
  • Ways in which a program processes:
  • Interpreted: Facilitates debugging and tuning.
  • Compiled: Necessary in languages with complex syntax; increases execution speed.

Criteria for Implementation

  • Lay-out: Schema deployment of equipment, machinery, and other plant elements.
  • Control Architecture: Both hardware and software.
  • Choice of Equipment: In particular, the ROBOT.
  • Security: Specially treated as machines with automatic operation appear.
  • Economic Rationale for Implementation

Resolution

The minimum increase that the control unit accepts. Limited by electronic sensors, converters, etc.

Accuracy

The distance between the planned value and the average value of the points actually achieved. Calibration errors, distortion, modeling, etc.

Repeatability

The radius of the area that covers the points made by the robot after many moves. Because of the mechanical system: friction, hysteresis, dead zones, etc.