Medical Robotic System Force Feedback via Joint Current
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Solution Overview
Problem
Current minimally invasive surgical technologies face challenges such as limited movement freedom, difficulty in accurately controlling instruments, and inability to effectively transmit force feedback to surgeons, leading to increased complexity and error in procedures.
Innovation Solution
A medical robotic system with a contact detection unit, current measurement unit, position/velocity measurement unit, and external force calculation unit that measures and calculates the contact force between surgical instruments and tissue, allowing for precise force reflection to the surgeon's hand, while improving time delay characteristics and maintaining positioning accuracy without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force sensors are directly connected to actuators to measure torques, then force measurement capability is improved, but additional position errors are induced due to the measurement means
Solution Approach 1:
The patent introduces an intermediary calculation method that uses easily measurable quantities (joint currents, positions, velocities) combined with a motor model to derive contact forces, rather than directly measuring forces with sensors that would interfere with position accuracy. The motor model acts as a mediator to convert electrical measurements into force information.
Solution Approach 2:
The patent replaces the mechanical force measurement system (physical force sensors) with an electrical measurement system combined with computational modeling. By measuring joint currents and using a motor model to calculate the relationship between current and torque, the system substitutes direct mechanical force measurement with an electrical-analogous approach that avoids position errors.
2Measurement precision
If torque sensors are attached to actuators to remove friction and rotor inertia effects, then force measurement accuracy is improved, but additional position errors and system complexity are introduced
Solution Approach 1:
The patent makes the motor itself serve dual purposes: both actuation and force measurement. By utilizing the motor's inherent electrical characteristics (current-torque relationship) and incorporating friction and inertia compensation within the control algorithm, the system eliminates the need for separate force sensors. The motor model includes parameters for friction and rotor inertia that are used to compensate for these effects in the force calculation.
3Measurement precision
If force/torque sensors are attached at end effectors to remove friction and rotor inertia effects, then force measurement is improved, but additional expenses, sterilization requirements, and EMI problems are generated
Solution Approach 1:
The patent extracts the force measurement function from the end effector and relocates it to the actuator level through electrical measurements. By measuring joint currents and using the motor model to calculate contact forces, the system removes the need for physical force sensors at the end effector, thereby eliminating sterilization requirements and EMI vulnerabilities in that critical location.
4Measurement precision
If macro-micro system is used to reduce inertia and friction of micro system, then force measurement capability is improved, but time delay problems occur
Solution Approach 1:
The patent merges the force measurement and actuation functions into a unified system at the actuator level. By using the same motor and control system for both purposes, the patent eliminates the time delay inherent in separate macro-micro systems with multiple sensors and communication interfaces. The force information is obtained directly from motor current measurements with minimal processing delay.
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
Enables precise force measurement and intuitive surgery by accurately transmitting contact forces to the surgeon, improving time delay characteristics and preventing positioning accuracy deterioration without additional expenses or EMI issues.
Implementation Method 1
the contact detection unit is configured to detect a contact of the surgical instrument with tissue of a patient
Implementation Method 2
the contact detection unit is configured to detect a contact of the surgical instrument with tissue of a patient
Implementation Method 3
a current measurement unit configured to measure a joint current in the robotic arm assembly
Implementation Method 4
a position/velocity measurement unit configured to measure a joint position and a joint velocity in the robotic arm assembly
Implementation Method 5
The force-reflecting control technique utilizes a Lorentz force actuator where an input current is output as a torque of a joint
Implementation Method 6
it is necessary for this technique to compensate components associated with friction, rotor inertia and structural vibration in a real motor
Implementation Method 7
it is necessary for this technique to compensate components associated with friction, rotor inertia and structural vibration in a real motor
Data Source
AI summary
A medical robotic system and method for controlling the system are provided to precisely measure contact force during the minimally invasive surgery. In one embodiment, a medical robotic system includes an input device, a robotic arm assembly, a surgical instrument operably coupled to the robotic arm assembly, the surgical instrument including a contact detection unit configured to detect a contact of the surgical instrument with tissue of a patient, a current measurement unit configured to measure a joint current in the robotic arm assembly, a position/velocity measurement unit configured to measure a joint position and a joint velocity in the robotic arm assembly, an external force calculation unit configured to calculate size and direction of a contact force caused by the contact of the surgical instrument to the tissue based on the joint currents, positions and velocities measured when the contact is occurred and measured when the contact is not occurred.