robots 1

• Robots


  • Come in all different shapes and sizes
  • Frequently classed by their degrees of freedom
• Degrees of freedom


  1. Each direction of movement on the robot is considered an axis of movement

  2. Single movement axis is equal to one degree of freedom
• Robot


  • Rotates at the waist
  • Bends forward and back at the shoulder
  • Moves vertically at the elbow
• Degrees of freedom


  This particular robot is equal to six degrees of freedom
• Degrees of freedom


  1. Moves along one axis for each of the waist, shoulder and elbow joints

  2. Moves along three axes at the wrist using pitch, roll and yaw
• Position axes


  Help to locate the tool in the work area
• Most robots have at least three position axes to help position the tool in the work area
• If the robot were to slide along a track it would have a fourth position axis of linear movement and another degree of freedom
• Orientation axes


  Help orient the tool in relation to the workpiece
• Types of movement along orientation axes

  • Pitch
  • Roll
  • Yaw
• Orientation axes movement


  • Pitch moves the tool vertically
  • Roll rotates the tool about its center axis
  • Yaw turns the tool left and right
• The position axes movement at the waist, shoulder and elbow along with the orientation axes movement of pitch, roll and yaw allow the robot to accomplish its tasks within the work envelope
• Today's webinar is on hazard analysis and risk assessments of collaborative robots
• The webinar will show the analysis of various hazards and ways to mitigate risk relevant to ISO 15066, which is a supplement and support to ISO 10218 for industrial robot safety standards, and is more geared towards collaborative robots
• The webinar will provide an overview of the HAZOP (Hazard and Operability) analysis and how it helps organize and identify risks associated with collaborative robot systems
• Hazard


  A potential source of physical injury or damage to health, property, or the environment
• Hazardous event


  An event that may result in harm
• Risk


  The likelihood and consequence of an event
• Types of robot-related hazards in ISO 15066

  • Robot-related hazards
  • Robot system-related hazards
  • Application-related hazards
• Robot-related hazards


  • Robot characteristics (speed, force, momentum, torque, power)
  • Geometry and surface of the robot
• Robot system-related hazards


  • End effector design
  • Operator motion and location with respect to parts
  • Fixture design
  • Manually controlled robot guiding devices
  • Surrounding environment
• Application-related hazards


  • Process-specific hazards
  • Limits caused by personal protective equipment
  • Ergonomic design
• Task identification


  1. Identify additional hazards from specific tasks performed by the operator

  2. Consider fluency and duration of robot-operator collaboration

  3. Frequency and duration of contact

  4. Transitions between non-collaborative and collaborative operation

  5. Automatic or manual restart

  6. Tasks involving more than one operator

  7. Human error
• Quasi-static contact


  Operator body part pushed against a fixed surface by the robot, where the operator cannot move away for more than 0.5 seconds
• Transient contact


  Robot arm hitting the operator in free space, where the operator can immediately get away from the hazard
• Quasi-static contact has a lower tolerable pain threshold compared to transient contact
• Power and force limiting

  1. Limit power and force through control or design, considering intended contact, incidental contact, and failure modes leading to contact

  2. Use force limiting, automatic shutoff after contact, and enhanced operator training to mitigate risks

  3. Implement mechanical integrity programs and review controller code to avoid failure modes leading to contact
• Ant damage


  • Can have automatic shutoff after contact
  • A lot of robots are going to be designed so that it'll immediately detect when it hits a body part or just another object and the robots going to immediately shut down
• Operator training procedures


  • Can enhance to hopefully avoid human error as much as possible
• Failure modes leading to contact situations

  Mechanical or controller error resulting in contact with the operator
• Avoiding failure modes leading to contact

  1. Mechanical integrity program

  2. Review controller code

  3. Procedures to keep operator in area only during dedicated collaborative work phase
• Potential contact events


  • Eliminate possibility for operator being struck in head or face area
  • Consider biomechanical limits and tolerance of different body parts
  • Origin of contact events
  • Probability or frequency of occurrence
  • Quasi-static or transient contact
  • Contact area, speeds, forces, pressures, momentum
• Steps to achieving robot risk reduction

  1. Identify conditions in which contact could occur

  2. Evaluate risk potential for such contact events

  3. Design robot and collaborative workspace so contact is infrequent and avoidable

  4. Apply risk reduction measures to keep contact situations below threshold limits
• Passive risk reduction


  Addresses mechanical design of robot system
• Passive risk reduction measures

  • Increase contact surface area with routed edges, smooth surfaces, compliant surfaces
  • Absorb energy, extend energy transfer time, reduce impact forces
  • Formal components and compliant joints/links
  • Limit moving masses
• Active risk reduction


  Addresses controller design of robot system
• Active risk reduction measures

  • Force limiting
  • Velocity limiting
  • Eliminate momentum, mechanical power, energy
  • Sensing to anticipate and detect contact
  • Safety rated soft axis and space limiting function
  • Safety monitored stop function
• Biomechanical limits criteria


  Based on pain sensitivity of each body part, with different tolerances for quasi-static and transient contact
• Biomechanical limits are based on conservative estimates and scientific research of pain sensation
• Excelencia PHA tool


  Used to perform hazard analysis and risk assessments, creating an organized list of hazards, likelihoods, consequences, safeguards, and recommendations