ISO/TS 15066

ISO/TS 15066 defines four distinct safety-rated modes that enable collaboration:

• Safety-rated monitored stop: The robot stops when a human enters the collaborative workspace and only restarts after the human leaves.
• Hand guiding: An operator physically grasps and directs the robot arm, with the robot providing compliant motion support.
• Speed and separation monitoring: The robot's speed is dynamically controlled based on the calculated separation distance from a human, ensuring it can stop before contact occurs.
• Power and force limiting (PFL): The robot's inherent design limits its power and force to biomechanically safe levels, allowing for intentional or incidental contact. PFL is the only mode designed for sustained or transient contact and is the primary focus of the specification's biomechanical limits.

The specification provides pain threshold data for transient (brief, non-clamping) contact across 29 body regions. These limits are the maximum permissible forces and pressures a robot can exert without causing injury. Key principles include:

• Limits vary significantly by body part (e.g., forehead vs. fingertip).
• Data is based on psychophysical studies where human subjects reported pain onset.
• Values are presented as curves correlating force (N) with pressure (N/cm²).
• Engineers must use the more restrictive value from the force/pressure curve for their risk assessment. This data is fundamental for designing and validating Power and Force Limiting (PFL) systems.

For quasi-static contact—where body part can be clamped or trapped against a rigid structure—ISO/TS 15066 defines even stricter force limits. Critical considerations:

• These limits prevent pain, minor injuries (bruising, pinching), and potential bone fracture.
• They account for the increased risk from sustained pressure and limited blood flow.
• The specification provides a simplified table of maximum permissible forces for various body regions under clamping conditions. System designers must ensure robots cannot exert forces exceeding these thresholds, often requiring sensitive torque sensors in each joint and fast-acting safety controllers.

ISO/TS 15066 mandates a rigorous, documented process. It is not a stand-alone standard but supplements ISO 10218-1 and ISO 10218-2.

• Hazard Identification: Systematic identification of all potential hazards in the collaborative application.
• Force/Pressure Calculation: Estimation of expected contact forces based on robot mass, velocity, geometry, and workspace layout.
• Comparison to Limits: Validating that calculated forces/pressures are below the biomechanical thresholds for the relevant body regions.
• Protective Measures: Implementation of technical safeguards (e.g., padded surfaces, rounded edges, force/torque sensing).
• Validation Testing: Physical testing, often using a pressure-sensitive film or force sensor, to verify safety under worst-case conditions.

The specification provides concrete engineering guidance to minimize injury risk during contact:

• Radii of Curvature: Recommends minimum radii for robot surfaces (typically ≥3mm) to distribute contact force and increase surface area, thereby reducing pressure.
• Surface Properties: Advises the use of compliant, smooth, and non-abrasive materials to reduce friction and shear forces.
• Geometry Avoidance: Prohibits shapes that can hook, snag, or clamp body parts or clothing.
• Dynamic Considerations: Requires analysis of robot stopping performance and braking distances within the collaborative workspace. These principles move safety from a purely control-system problem to a holistic mechanical design challenge.

ISO/TS 15066 cannot be applied in isolation. Its full context is within the broader robot safety ecosystem:

• ISO 10218-1: The 'Requirements for the robot manufacturer.' Defines inherent safe design requirements for the robot itself.
• ISO 10218-2: The 'Requirements for the robot system integration.' Guides the safe integration of the robot into a complete workcell.
• ISO/TS 15066: Provides the collaboration-specific data and methods needed to fulfill the requirements of Parts 1 and 2 for collaborative applications. Compliance requires adhering to all three documents, with ISO/TS 15066 providing the critical biomechanical justification for contact scenarios.

Power and Force Limiting (PFL) is one of the four defined collaborative operation modes in ISO/TS 15066. It is a safety function where the robot's inherent design or active control limits the power and force it can exert. The specification provides biomechanical limits for transient and quasi-static contact based on body region sensitivity (e.g., face, hand, abdomen).

• Transient contact: Short-duration impact (e.g., robot arm bumping a person). Limits are defined by maximum pressure and force.
• Quasi-static contact: Prolonged clamping or trapping (e.g., a person's body part is pinned). Limits are defined by maximum pressure.

PFL is the mode that enables true physical collaboration without separation.

A Safety-Rated Monitored Stop is a collaborative operation mode defined in ISO/TS 15066. When a human enters a predefined collaborative workspace, the robot performs a controlled, safety-rated stop. All motion ceases, but the robot remains powered and ready. Motion automatically resumes only after the human has left the monitored zone. This mode is used for tasks where the robot and human work in sequence, not simultaneously, within the same space. It requires presence-sensing devices (e.g., light curtains, laser scanners, vision systems) with a Safety Integrity Level (SIL) or Performance Level (PL) suitable for risk reduction.

Hand Guiding is a collaborative operation mode where a human operator physically grasps a robot's end-effector or a dedicated handle and manually moves the robot arm to perform a task or teach a path. During this mode:

• The robot's actuators enter a compliant state, often using torque sensing to follow the human's lead with minimal resistance.
• A enabling device (a dead-man switch) must be continuously activated by the operator for motion to occur.
• Speeds are limited for safety.

This mode is central to kinesthetic teaching and is explicitly addressed in ISO/TS 15066, which requires safeguards against unintended movement or excessive force during guidance.

Speed and Separation Monitoring (SSM) is a collaborative operation mode defined by ISO/TS 15066. It uses safety-rated sensors to continuously monitor the distance between a human and the robot. The robot's speed is dynamically controlled based on this separation distance:

• Larger separation: The robot may operate at full speed.
• Decreasing separation: The robot's speed is reduced.
• Minimum separation distance breached: The robot performs a protective stop before contact can occur.

The system maintains a protective separation distance that accounts for robot stopping time, human intrusion speed, and sensor/system response time. This allows for concurrent work in close proximity.

Physical Human-Robot Interaction (pHRI) is the subfield of robotics focused on scenarios involving direct physical contact and force exchange between a human and a robot. This contrasts with social HRI, which focuses on communication. pHRI is the primary domain governed by ISO/TS 15066.

Key research and engineering challenges in pHRI include:

• Compliant control algorithms (e.g., impedance/admittance control)
• Contact detection and reaction strategies
• Intuitive physical collaboration for tasks like co-carrying
• Hardware design for safe mechanics and force sensing

ISO/TS 15066 provides the safety framework that makes applied pHRI possible in industrial settings.