Characterizing the Coefficient of Friction Between a Capsule Robot and the Colon

Gastroenterology Medicine Bioengineering Biophysics Life Sciences
coefficient of friction contact pressure hoop strain sliding velocity capsule robot traction force locomotion resistance

Characterizing the Coefficient of Friction between a Capsule Robot and the Colon

Background

Traditional colonoscopy, while effective for assessing colon health, is highly invasive, causing discomfort and potential complications. To address this issue, researchers have developed capsule robots (CR) with active movement mechanisms to achieve colon inspection with lower invasiveness. However, to realize effective movement and control of CR, accurately predicting the traction force and movement resistance, primarily contributed by friction, is critical. Currently, detailed research on the coefficient of friction (CoF) within the colon is lacking in the literature. Therefore, this paper aims to determine the quantitative relationships between the friction coefficient and contact pressure, circumferential strain, and sliding speed through experimental measurements and data analysis.

Paper Source and Author Information

The paper titled “Characterizing the coefficient of friction between a capsule robot and the colon” has been accepted by the “IEEE Transactions on Biomedical Engineering”. The authors of the paper include Jinyang Gao, Peng Huang, Qiulin Tan (North University of China), Jinshan Zhou (China University of Mining and Technology), Ruiqin Li (Shanxi Key Laboratory of Advanced Manufacturing Technology), Guozheng Yan (Shanghai Jiao Tong University), and Li Zhang (The Chinese University of Hong Kong). The research was supported by the National Natural Science Foundation of China and the Shanxi Provincial Science Foundation.

Research Process

In this study, the authors designed a series of experiments and data analysis processes to determine the friction coefficient within the colon. The main processes are as follows:

1. Experimental Design

The research utilized a classic traction experimental setup to study the friction coefficients of three commonly used materials for CR (PDMS, white ABS plastic, and transparent ABS plastic) under different conditions. The experiment involved the following steps:

  • Colon Inversion and Fixation: The pig colon was inverted to expose the inner surface and fixed on a support board, while thin tubes were adjusted to change the circumferential strain.
  • Friction Sample Preparation: PDMS strips (with triangular patterns), white ABS plates, and transparent ABS plates were used as friction samples.
  • Loading and Dragging: Using a force gauge and a linear rail module, the samples were dragged to measure the traction force under different contact pressures, circumferential strains, and sliding speeds.

2. Data Measurement and Analysis

During the experiments, 144 different friction scenarios were set up by adjusting contact pressure (500 Pa to 6250 Pa), circumferential strain (0%-60%), and sliding speed (1 mm/s to 10 mm/s). The primary observations were:

  • Effect of Contact Pressure on CoF: Results indicated that as contact pressure increased, the friction coefficient generally decreased. This is attributed to increased contact pressure squeezing more mucus out, reducing the lubrication effect.
  • Effect of Circumferential Strain on CoF: As circumferential strain increased, mucus release was enhanced, significantly lowering the CoF.
  • Effect of Sliding Speed on CoF: With an increase in sliding speed, the friction coefficient increased. This is because high sliding speeds reduce stress relaxation in the colon tissue, increasing environmental resistance and viscous friction.

3. Data Models and Fitting

To quantitatively describe the relationship between the friction coefficient (CoF) and contact pressure, circumferential strain, and sliding speed, the authors conducted the following steps:

  • Fitting the Combined Effect of Contact Pressure and Circumferential Strain: By measuring and fitting curves, a power function was derived to describe the relationship between CoF and contact pressure and circumferential strain.
  • Fitting the Effect of Sliding Speed: By comparing experimental data across different sliding speeds, a function describing the impact of sliding speed on CoF was derived.

Ultimately, a general formula describing the friction coefficients of the three materials was established, containing eight fitting constants. The fitting effectiveness was high, with correlation coefficients reaching 0.9822, 0.9286, and 0.9696, respectively.

Main Results

The derived friction coefficient formula was applied to predict the traction force and movement resistance of CR in the colon and was subjected to actual measurements:

  • Prediction of Traction Force and Movement Resistance: Using the determined friction coefficient formula, calculations were conducted and validated in practical experiments within pig colons. The results showed a high consistency between calculated and actual measurements, indicating the accuracy of the friction coefficient formula.

Conclusion and Significance

This research systematically reveals the multi-factor influences on the friction coefficient within the colon and establishes a quantitative formula for the friction coefficient based on these influences. The study shows that the formula can accurately predict the traction force and movement resistance of CR, laying a foundation for better mechanics and movement control. This result is significant not only for the application of capsule robots in colon inspection but also provides scientific evidence for other interventional medical devices, such as magnetically controlled capsule robots and vibrating impact capsule robots. By precisely predicting frictional forces, the safety and effectiveness of operations can be improved.

Research Highlights

  • Comprehensive Measurement of Friction Coefficient: Systematic measurement and analysis of the friction coefficients of three commonly used materials under different contact pressures, circumferential strains, and sliding speed conditions, filling a gap in the literature.
  • Revealing Multi-Factor Influence Laws: Systematically reveals the interdependence of contact pressure and circumferential strain, as well as the independent impact of sliding speed on the friction coefficient.
  • Fitting of the Friction Coefficient Formula: Proposed a precise quantitative formula for the friction coefficient through experimental data and fitting, providing a scientific foundation for the design and interaction mechanics control of future capsule robots.

This research not only provides vital data support and theoretical basis for the development of capsule robots but also enhances the feasibility and precision of operating medical devices within the complex environment of the colon.