Collaborative Robot Low Drive Ratio Transmissions
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Solution Overview
Problem
Current collaborative robots are limited by high collision forces and reduced productivity due to the need for safety barriers and sensors, which slow them down and increase costs, making it difficult to operate safely and efficiently near humans.
Innovation Solution
A robot design with low drive ratio transmissions and dynamic feedforward control, allowing for reduced reflected inertia and motor torques, enabling safe operation at higher speeds while complying with ISO TS 15066 regulations by limiting feedback error torques and employing a dynamic model for real-time motor torque calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If traditional high drive ratio transmissions are used, then the robot has high torque capability, but the reflected inertia is high causing high collision forces
Solution Approach 1:
The patent changes the drive ratio parameter from traditional high ratios (e.g., 100:1) to low ratios (e.g., 10:1 or direct drive 1:1). This parameter change reduces the reflected inertia significantly while maintaining adequate torque capability through optimized motor selection and control strategies, thereby reducing collision forces to safe levels.
Solution Approach 2:
The patent replaces traditional mechanical reduction gears with direct drive motors or low ratio transmissions. This substitution eliminates the mechanical complexity of high ratio gear trains and their associated reflected inertia, using instead electronically controlled motor systems that provide torque control without mechanical multiplication of inertia.
2Productivity
If the robot operates at high speed, then productivity is improved, but collision forces increase making it unsafe for collaborative operation
Solution Approach 1:
The patent changes the kinetic energy parameter by reducing the robot's effective mass through low drive ratio transmissions. By reducing reflected inertia, the robot can operate at higher speeds while keeping kinetic energy (and thus collision forces) within safe limits defined by ISO 15066 standards.
Solution Approach 2:
The patent implements real-time feedback control systems that monitor robot motion and adjust motor torques dynamically. This feedback control ensures that even at high speeds, any collision will result in forces within safe limits by rapidly modulating the actuator outputs based on actual motion deviations.
3Reliability
If sensors are added to detect humans and slow down the robot, then safety is improved, but cycle time increases reducing productivity
Solution Approach 1:
The patent converts the potential harm of high-speed collisions into a benefit by designing the robot with inherently low collision forces through direct drive. This allows the robot to maintain high operating speeds without requiring safety sensors to slow it down, as the robot's physical design ensures collisions are safe by default.
Solution Approach 2:
The patent extracts and removes the need for safety sensors and speed reduction mechanisms by fundamentally changing the robot's drive system. Instead of using sensors to manage safety, the low drive ratio design inherently provides safe operation, eliminating the time losses associated with sensor-based safety systems.
4Reliability
If touch sensors are added to enable collision detection, then safety response is improved, but the robot must operate slower to allow adequate reaction time
Solution Approach 1:
The patent takes preliminary action by designing the drive system with low reflected inertia from the start, before any collision occurs. This preliminary design choice ensures that even at high operating speeds, the robot's kinetic energy remains low, eliminating the need to slow down for safety reasons while maintaining the ability to detect and respond to collisions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly increases the safe operating speed of collaborative robots, reducing collision forces and maintaining compliance with safety standards, thus enhancing productivity and justifying their use in closer proximity to humans.
Implementation Method 1
allowing for reduced reflected inertia and motor torques
Implementation Method 2
employing a dynamic model for real-time motor torque calculation
Data Source
AI summary
A collaborative robot employs low ratio drives for three or more axes of movement, such as three primary axes. An arm assembly may be mounted to a support for movement along a vertical linear axis, and the arm assembly may include first and second arm links that are each rotatable about vertical axes, e.g., such that the arm links move in a horizontal plane. Low ratio drives may be used for movement along the vertical linear axis and the rotary axes for the first and second arm links. Feedforward and feedback control may be employed to control the movement of the arm assembly and arm links, and feedback torque components may be limited to 25% or less of the maximum drive torque.