Abstract: Insufficient structural stiffness and positioning accuracy remain critical challenges for continuum robots with underactuated configurations.Inspired by spinal biomechanics,an antagonistic tension-coupled cam-spring mechanism was developed to regulate the stiffness of tendon-driven continuum robots.The mechanism integrates a phase-coordinated compact actuator with an elastic hollow cam,enabling stiffness modulation through simplified actuation input.Compared with conventional architectures that employ an independent motor for each tendon,the proposed design reduces the number of motors by 75%,leading to a more compact structure and lower control complexity.Experimental evaluation was conducted on both resin-based and stainless-steel continuum robots.Results show that the equivalent stiffness increased by 314% for the resin structure under a 30g load and by 76% for the stainless-steel structure under a 100g load.The additional end-effector displacement caused by loading remained within 0.209~0.554mm for the resin robot and 0.132~0.166mm for the stainless-steel robot.Despite the inherent flexibility of the structure,repeatability was significantly improved,and positioning error decreased by 56%~84%.The proposed mechanism provides an effective approach for stiffness enhancement and precision control of continuum robots,supporting their application in high-precision scenarios such as minimally invasive medical procedures.