Due to the increasing influence of human engineering activities, it is important to monitor the transient disturbance during the evolution process of landslide. For this purpose, a high-performance piezoelectric sensor is presented in this paper. To adapt the high static and dynamic stress environment in slope engineering, two key techniques, namely, the self-structure pressure distribution method (SSPDM) and the capacitive circuit voltage distribution method (CCVDM) are employed in the design of the sensor. The SSPDM can greatly improve the compressive capacity and the CCVDM can quantitatively decrease the high direct response voltage. Then, the calibration experiments are conducted via the independently invented static and transient mechanism since the conventional testing machines cannot match the calibration requirements. The sensitivity coefficient is obtained and the results reveal that the sensor has the characteristics of high compressive capacity, stable sensitivities under different static preload levels and wide-range dynamic measuring linearity. Finally, to reduce the measuring error caused by charge leakage of the piezoelectric element, a low-frequency correction method is proposed and experimental verified. Therefore, with the satisfactory static and dynamic properties and the improving low-frequency measuring reliability, the sensor can complement dynamic monitoring capability of the existing landslide monitoring and forecasting system.

This article presents a quasi–zero-stiffness isolator with a cam-based negative-stiffness mechanism, where the cam has a user-defined noncircular profile to generate negative stiffness to counterbalance the positive stiffness of the vertical spring and yield the quasi–zero-stiffness characteristic around the equilibrium position. Unlike previous studies, the proposed quasi–zero-stiffness isolator has the preferable feature that the desired cubic restoring force can be directly obtained through the well-designed profile of the cam in the negative-stiffness mechanism with the friction considered during the model design, rather than through the Taylor expansion and friction-ignoring assumption, which can avoid the approximation error between the theoretical design and the specific realization. The pure-cubic nonlinear differential equation of motion of the quasi–zero-stiffness isolator is derived and solved with the harmonic balance method, followed by the discussion of the relevant dynamic characteristics. Experimental studies are carried out based on the physical prototype of the quasi–zero-stiffness isolator. The results show that the quasi–zero-stiffness isolator can greatly extend the isolation frequency bandwidth and has a much lower resonance peak. In the low-frequency band, the quasi–zero-stiffness isolator greatly outperforms the corresponding linear system but is equivalent or even inferior in the high-frequency range with the increase of excitation force.

Due to the quasi-zero-stiffness and overload protection characteristics, constant-force mechanisms can be widely used in nonlinear vibration control, high-efficiency shock isolation, and other engineering fields. As a preparatory work for the further applications, this paper presents a cam-based constant-force compression mechanism and validates the quasi-static characteristics experimentally. By employing the friction considered profile identification method to design the cam and through the interaction between the cam and spring-sliders, the constant-force compression mechanism can passively output the desired constant force over a sufficiently large displacement. The design theory is firstly introduced in detail. Through establishing and solving the differential relationship between the lateral elastic force and vertical constant force, the constant-force compression mechanism under various frictional conditions can be designed. Then, constant-force compression mechanism prototypes corresponding to sliding and rolling friction are designed, fabricated and tested respectively. The results show that both the prototypes have the satisfactory characteristics as with the design requirements. Moreover, the relative generality and stronger engineering applicability of the proposed friction considered profile identification method are proved since it can not only cover the frictionless (micro-friction) cases, but keep the constant-force behavior of the constant-force compression mechanism under the nonignorable friction conditions. Therefore, compared with the existing cam-roller constant-force mechanisms that must ensure the ignoring micro-friction demand, the presented constant-force compression mechanism taking friction into consideration has important engineering significance since it can reduce this machining requirement.

No abstract

This paper presents the design and experimental validation of two force regulation mechanisms (FRMs) containing a translational cam and a rotational cam, respectively. With the friction-considered profile identification method (FCPIM) to define the cam and through the squeezing between the cam and the spring-supported slider, the FRMs can passively output the desired force over the designed displacement. Under the premise of that the friction coefficient can be accurately obtained, the friction-considered design principle will be significant for the realization of FRMs in actual applications since it is no longer necessary to achieve high accuracy by pursuing the frictionless condition. Hence, the conventional materials and mechanical parts can be directly used to assemble the FRMs without sacrificing the force regulating accuracy. We are highly interested in the actual experimental behavior of the proposed FRMs under the friction-considered condition. Then, prototypes of the two FRMs capable of outputting multiple types of forces including in zero-stiffness, positive and negative stiffness are specially designed, fabricated, and tested quasi-statically. The experimental results verify the correctness of FCPIM since they agree with the design objective well. Meanwhile, the effectiveness of the FCPIM is proved as the errors of the experimental results considering friction is much lower than those ignoring friction. The experiments also show that the noise phenomenon in the testing curves that may affect the judgment of test accuracy can be highly degraded by using more stable and controllable loading tools, which is helpful for future research.