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Smart feedback systems in modern robotics
Aljaž Ogrin
Product manager for absolute encoders
RLS & Renishaw
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Aljaž Ogrin
From company RLS (Rotary and Linear Sensors), Slovenia
Specialized in magnetic encoder technologies
Associate company of Renishaw – global leader of metrology products
Electronics engineer
Working in Encoder division for 16 years
Working closely with the robotic market for past 5 years
About the presenter
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RLS and Renishaw supply feedback systems to the worldwide market. Working closely with robotic market for many years gives us an interesting view of global markets and gives a broad overlook of current market status and hints about trends and future developments in robotic market.
Today’s Focus:
• Detecting future trends in which direction(s) robotic builders and end-customers are researching.
• Analyzing the importance and influence of feedback systems to overall application performance.
• Industrial and Collaborative Robot market
• Interesting case studies: Autonomous vehicles, unmanned flying and deep-sea systems
Abstract & Learning objectives
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• Industrial (classic) robots for heavy duty factory automatization
• Smaller task automatization; more versatile
• Consumer robots; home assistance;
intelligent toys
• Highly specialized applications
(military, medical)
Robotic market sectors
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Every robot movement requires a feedback
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• Industrial robots – medium to high performance; proprietary solutions
• Collaborative robots – safety functions, complex functions, compact
• Service robots (home assistance) – low performance, low price
• Mobile robots and Agriculture autonomous vehicles – robust, waterproof
• Medical / surgical robots – small, lightweight, reliable
• Student learning & research projects – new technologies
• Direct drive motors for automatization – universal, high performance
Robotic market sectors & requirements for feedback
Market status
Mature
Big growth
Slowly rising
Rising
Rising
Rising
Slowly rising
Robotic system design
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Robot
(motors & feedback)
Bulky cable
(multi-conductor)
Control cabinet
(logic, power, drives)
Production supervision
(computer)
Robotic arm system development
Smart Robot
(integrated drives & logic)
Power cable / batteries
(without cabinet)
Wireless network / fibre optic
Integrated robot
(integrated drives)
Small cable
(power & bus)
Control cabinet
(logic, control panel)
Mesh network
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Typical robotic joint
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• Current / commutation loop
• Velocity loop
• Position loop
Closed loop drive systems 1
INC
INC ABS
3xHALL
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Current / commutation loop
+
Velocity loop
+
Position loop
Running from a
single encoder
Closed loop drive systems 2
ABS (high res)
ABS + multiturn
OR
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Encoder error types
Source: Poor installation (eccentric mounting of rotor injects 1st order error)
Effect: Low frequency error
Result: Vibration, incorrect positioning
Smooth movement & encoder error
Source: Sub divisional error (low performance encoder); Noise (wrong installation - air gap)
Effect: High frequency error
Result: Noise in system, energy loss
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LATENCY
Total system accuracy
=
Mechanical accuracy (eccentricity)
+
Encoder target (scale) accuracy
+
Electrical accuracy (SDE, noise)
+
Processing delay (latency)
Forgotten technical detail
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• Mounting must be intuitive (reduce design time, short time to market)
• Wide installation tolerances (cheaper manufacturing, reduce assembly time)
• Plug’n’play
• Monitoring of parameters (runtime diagnostics)
• Data logging in production line allows full traceability
Design considerations (requirements for the encoder)
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• Two encoders per axis (fully redundant) – no need for safety
• One encoder per axis – redundancy via sensorless motor commutation feedback
• Lots of safety features and safety checkpoints is recommended and welcome
Good result of safety assessment
• SIL (Safety Integrity Level) standards are not required (yet); done on system level
Safety and reliability
Industrial robots
vs.
Collaborative robots
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Classic robotic arms
Industrial robots (classic)
Motors on the outside
On-axis encoders on the motors
Lightweigth & collaborative
Smaller, cheaper
Motors, encoders inline inside the joint
Hollow shaft encoders
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Industrial
Collaborative
Drive train of a classic robotic arm
Servo motor with encoder
Incremental encoder
Absolute encoder
Gear box End point
Gear box End point DDR motor
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Typical configuration:
• Incremental encoder on a motor shaft (velocity feedback)
• Absolute encoder at the output shaft (position feedback)
• No influence by gearbox error, precise control
• Redundant feedback due to 2 encoders
• True absolute – knows the position after power-up
• Through hole, no slip rings for cables
• Compact size, easy integration
• A lot of safety features
• Fast communication interface
Requirements for a feedback system for a collaborative robot
Applications
Case studies
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Robotic market sectors & requirements for feedback
COLLABORATIVE
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Robotic market sectors & requirements for feedback
GIMBALS
• Flying
• Handheld
• Underwater
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Robotic market sectors & requirements for feedback
OFF-ROAD VEHICLES
Water transport, agriculture,...
ON-ROAD VEHICLES
Automotive standards, (ASIL)
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• .
Robotic market sectors & requirements for feedback
SURGERY,
MEDICAL
FDA approval on complete system, not encoders
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Robotic market sectors & requirements for feedback
RESEARCH &
EDUCATION
