Spring-Free Legged Robot Foot with Active Velocity Control
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Solution Overview
Problem
Legged robots face challenges in controlling impact forces during movement due to high reflected inertia and lack of mechanical compliance, leading to potential damage and instability, especially when performing general tasks that require precise foot placement and ground reaction force management.
Innovation Solution
A legged robot design featuring a multi-link elongated assembly with a light-touch foot assembly that minimizes initial impact forces by using a two-stage contact mechanism, where a foot actuator reduces the vertical velocity of the distal link to zero upon ground contact, eliminating the need for springs and allowing precise control of forces during stance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If mechanical compliance (springs) is used to reduce impact forces, then impact forces are reduced, but control difficulty increases
Solution Approach 1:
The foot assembly is divided into multiple segments (heel portion, toe portion, mid-portion) that contact the ground at different times. This segmentation allows the robot to control impact forces by managing ground contact in stages, with each segment serving a specific function in the touchdown sequence.
Solution Approach 2:
The foot actuator performs preliminary action by actively reducing the vertical velocity of the distal link before the main foot contact with the ground. This velocity reduction occurs during the transition phase, preparing the system for a controlled, low-impact touchdown and enabling precise force management from the outset of ground contact.
2Object-affected harmful factors
If foot velocity is reduced to near-zero before ground contact, then impact forces are minimized, but task performance capability is reduced
Solution Approach 1:
The system dynamically adjusts foot velocity based on the operational phase. During approach, velocity is actively reduced for controlled touchdown. During stance, velocity is maintained at appropriate levels for task performance. This dynamic control allows the robot to optimize for both impact reduction and task capability at different moments in the gait cycle.
Solution Approach 2:
Velocity reduction is performed as a preliminary action during the approach phase, not during ground contact. This timing allows the main foot contact to occur with minimized velocity (reducing impact) while still enabling subsequent task performance during the stance phase when velocity can be actively controlled for specific tasks.
3Ease of operation
If compliant materials are used on feet with force-sensing electronics, then ground reaction force control is enabled, but bandwidth limitations and oscillations occur
Solution Approach 1:
The patent replaces passive mechanical compliance (compliant materials and springs) with an active control system using foot actuators. Instead of relying on mechanical compliance to manage forces, the system uses sensors and actuators to actively control foot velocity and ground reaction forces, eliminating the bandwidth limitations and oscillations associated with passive mechanical compliance.
Solution Approach 2:
The system employs feedback control through force-sensing electronics and foot actuators that continuously monitor and adjust foot velocity and ground contact forces. This closed-loop feedback enables stable and responsive force control during both approach and stance phases, replacing the open-loop behavior of passive compliant materials.
4Measurement precision
If minimal mechanical compliance is used, then control precision is improved, but impact forces increase
Solution Approach 1:
The foot actuator performs preliminary velocity reduction as a proactive measure before ground contact occurs. This preliminary action allows the system to maintain minimal mechanical compliance (preserving control precision) while still achieving low impact forces through active velocity management during the approach phase.
Solution Approach 2:
The patent substitutes passive mechanical compliance with an active control system that uses sensors and actuators to manage impact forces. This substitution allows the system to maintain minimal mechanical compliance for control precision while using active control to reduce impact forces, resolving the contradiction between the two requirements.
Data Source
AI summary
A legged robot has legs that have multiple links, one of which is a distal link. A foot assembly for interacting with the terrain is disposed on a distal end of the distal link. As a robot takes a step, a portion of the foot assembly that has lower effective inertia than the rest of the foot assembly touches down first and acts to reduce the vertical velocity of the rest of the foot assembly before it reaches the terrain through the use of an actuator located on the distal or intermediate link.