Dynamic Physical Constraint for Haptic Hard Surface Emulation

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Solution Overview

Problem

Conventional haptic systems fail to accurately emulate hard surfaces due to issues like springiness, instability, and high friction, which are essential for precision tasks like surgical procedures, and require force sensors and bulky architectures.

Innovation Solution

A haptic method using a dynamic physical constraint that adjusts its position based on the user's location to prevent surface penetration, allowing for realistic hard surface emulation with minimal friction and no stickiness, applicable in various applications including surgery.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If impedance or admittance-generating algorithms are used to emulate hard surfaces, then the system can provide force feedback guidance, but the system experiences response lag, joint backlash, structural flex, and sensor noise causing instability and imprecision

Engineering Contradiction:

Improvestability and precisionVSAvoidresponse lag time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces traditional impedance/admittance control algorithms with a dynamic physical constraint mechanism that uses real-time geometric computation and direct force application. Instead of relying on feedback loops with inherent delays, the system computes the constraint force based on current position and applies it immediately, eliminating response lag and improving stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If a region of increasing robot stiffness is introduced at the boundary (Region II), then the transition between free motion and restricted regions becomes smoother, but springiness at the boundary and vibrating motion occur

Engineering Contradiction:

Improvesmooth transitionVSAvoidboundary stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The patent implements a dynamic physical constraint that adjusts its position and stiffness characteristics in real-time based on the user's location relative to the virtual surface. The constraint is soft when distant and becomes progressively stiffer as the user approaches the boundary, providing smooth transition without the springiness and vibration associated with fixed stiffness regions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system dynamically changes the stiffness parameter of the physical constraint based on the distance to the virtual surface. This continuous parameter adjustment allows for smooth transitions while maintaining boundary stability, avoiding the fixed stiffness problems that cause vibration and springiness.

Inventive Principle:

Principle #35Parameter changes

3Force

If force transducers and high-impedance motors are used to provide sufficient impedance, then hard surface emulation is achieved, but the robot becomes bulky with large parts and significant friction

Engineering Contradiction:

Improveimpedance forceVSAvoidrobot size and mass

Core Design Contradiction:

ForceVSWeight of moving object

Solution Approach 1:

The patent introduces a virtual surface as an intermediary between the user and the physical robot system. The hard surface emulation is achieved through computational geometry and virtual constraints rather than physical high-impedance components. This allows force feedback to be generated through software-based geometric computation and lightweight actuation, eliminating the need for bulky force transducers and high-impedance motors.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Adaptability or versatility

If continuously variable transmission (CVT) concept is used with continuous wheel steering, then transmission ratios are continuously adjustable, but hesitation occurs when user rapidly pushes the device and surface penetration occurs at high angles

Engineering Contradiction:

Improvecontinuous transmission ratio adjustmentVSAvoidresponse accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent pre-computes the virtual constraint surface and determines the appropriate constraint forces before the user interacts with the boundary. By having the constraint ready and pre-positioned based on the current state, the system responds immediately to user inputs without hesitation and prevents surface penetration even at high approach angles.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9037295B2Dynamic physical constraint for hard surface emulation

Publication Date: 2015.05.19 OMNI LIFE SCIENCE INC

AI summary

A method and apparatus for haptic hard surface emulation using a dynamic physical constraint are provided. The movement and position of the dynamic physical constraint is actively controlled in order to emulate a hard surface. The dynamic physical constraint may be controlled by a computer. In another aspect of the invention, the dynamic physical constraint limits the motion of a manipulator joint in space. The position at any time of the dynamic physical constraint is dependent on the position in space of the manipulator's end effector.