Shaoze Yan

Effects of damping, friction, gravity, and flexibility on the dynamic performance of a deployable mechanism with clearance

Space deployable mechanisms have been widely employed in modern spacecraft, and the dynamic performance of such mechanisms has become increasingly important in the aerospace industry. This article focuses on the dynamic performance of a deployment mechanism with clearance considering damping, friction, gravity, and flexibility. The modeling methods of revolute joint with clearance, close cable loop, and lock mechanism of a typical deployable mechanism are provided in this article. Based on these proposed methods, the dynamics model of a space deployable mechanism with clearance is established using the multi-body program ADAMS. The effects of clearance, damping, friction, gravity, and flexibility on the dynamic performance of a deployable mechanism in the deploying and locking processes are studied using simulations. The results reveal that the deployable mechanism exhibits evidently nonlinear dynamic characteristics, thus validating the significance of clearance, damping, friction, gravity, and flexibility in system dynamic performance.

A 3-DOFs mobile robot driven by a piezoelectric actuator

In this paper, a novel miniature-step mobile robot with three degrees of freedom (DOFs) is developed based on the inchworm principle. This device, driven by a piezo stack actuator, utilizes a rhombic flexure hinge mechanism and four electromagnetic legs to achieve large stroke translation and rotation with high resolution on a platform. The design process of the rhombic flexible frame and the electromagnetic legs is described. The electric circuits for generating appropriate voltage signals are designed to control the legs to clamp to and release from the platform. In order to investigate the motion characteristics of the device, a series of experiments was carried out. The experimental results confirm that the device is capable of performing a 3-DOFs motion with a high resolution on a platform. Furthermore, the platform loading capacity allows some additional devices like a gripper or any other device for a particular application to be mounted on board. This enables the devices potential in a wide variety of applications.

Kinematic accuracy analysis of flexible mechanisms with uncertain link lengths and joint clearances

A general method of kinematic accuracy analysis is presented for the flexible planar mechanisms with stochastic parameters such as uncertain link lengths and joint clearances. The impact-pair model is employed to describe the separation and impact phenomena between the two components in the clearance joint. The dynamic equations of the flexible mechanism with stochastic parameters are established by finite element method and solved by the Newmark method. The Monte Carlo method is introduced to analyse the kinematic accuracy of the flexible mechanisms. A numerical example shows the effects of link flexibility and joint clearances on the kinematic accuracy of the planar mechanism with stochastic parameters using the proposed approach.

Effects of erectable glossal hairs on a honeybee's nectar-drinking strategy

With the use of a scanning electron microscope, we observe specific microstructures of the mouthpart of the Italian bee (Apis mellifera ligustica), especially the distribution and dimensions of hairs on its glossa. Considering the erection of glossal hairs for trapping nectar modifies the viscous dipping model in analyzing the drinking strategy of a honeybee. Theoretical estimations of volume intake rates with respect to sucrose solutions of different concentrations agree with experimental data, which indicates that erectable hairs can significantly increase the ability of a bee to acquire nectar efficiently. The comparison with experimental results also indicates that a honeybee may continuously augment its pumping power, rather than keep it constant, to drink nectar with sharply increasing viscosity. Under the modified assumption of increasing working power, we introduce the rate at which working power increases with viscosity and discuss the nature-preferred nectar concentration of 35% by theoretically...

A Gripper Actuated by a Pair of Differential SMA Springs

This article presents a gripper actuated by a pair of differential shape memory alloy (SMA) springs. The mechanical structure of the gripper includes a pair of fingers, a coupler, a tension rod, a slider, and a frame. An experimental setup of the SMA gripper is established. The SMA actuator is heated by the electric current and cooled by fans. Thermal resistance sensors are used to measure the temperature of the SMA springs and a slide rheostat is used to sense the output displacement of the actuator. In order to evaluate the potential of the SMA actuator for application to the proposed gripper, three types of tests are performed as follows: influence of the cooling methods, heating current, and action frequency on the characteristics of the SMA actuator and the gripper. The experimental results show that the output displacement amplitude can increase by increasing the heating current and decreasing the action frequency. A good cooling method can increase the cyclic output displacement amplitude and the bandwidth of the SMA actuator. A proportional-integral (PI) controller is presented to control the output position of the gripper, and a two-phase control method is developed to reduce the overshooting of the system. Position control experiments for the SMA gripper are performed, and the experimental results demonstrate that a good position control performance of the gripper is obtained by using the proposed controller.This article presents a gripper actuated by a pair of differential shape memory alloy (SMA) springs. The mechanical structure of the gripper includes a pair of fingers, a coupler, a tension rod, a slider, and a frame. An experimental setup of the SMA gripper is established. The SMA actuator is heated by the electric current and cooled by fans. Thermal resistance sensors are used to measure the temperature of the SMA springs and a slide rheostat is used to sense the output displacement of the actuator. In order to evaluate the potential of the SMA actuator for application to the proposed gripper, three types of tests are performed as follows: influence of the cooling methods, heating current, and action frequency on the characteristics of the SMA actuator and the gripper. The experimental results show that the output displacement amplitude can increase by increasing the heating current and decreasing the action frequency. A good cooling method can increase the cyclic output displacement amplitude and the b...

Dynamic modeling and motion precision analysis of spacecraft manipulator with harmonic drive considering the alternate thermal field in orbit

Nowadays, the harmonic drive is widely used as the reducer in the spacecraft manipulator, which may influence the dynamical properties of flexible spacecraft manipulator. The alternative thermal environment makes the spacecraft manipulator to experience periodic heating and cooling in the sunlight and shadow region of the Earth. The analysis of dynamic modeling and motion precision of flexible spacecraft manipulator with harmonic drive, considering the alternate thermal field in orbit is of significant importance for spacecraft manipulator designers in the early stage of design. The thermal load influences the motion precision, which reflects whether the mechanism is performed normally or not. In order to evaluate the loss of motion precision, this paper establishes the dynamical model of spacecraft manipulator with harmonic drive considering the alternate thermal field in orbit. A thermal analysis model of flexible spacecraft manipulator with harmonic drive is developed to characterize the thermal response of the whole spacecraft manipulator system subjected to space heat flux. Two different altitudes including low Earth orbit and geosynchronous Earth orbit are considered. Moreover, the transient temperature fields in different orbits of spacecraft manipulator and the effects of the thermal environment factors on the spacecraft manipulator are investigated. Simulation results reveal the evolution process of the transient temperature field of the spacecraft manipulator system. According to the results, the maximum temperature difference for space manipulator can lead to more severe precision loss compared with the minimum temperature difference. In addition, the vibration frequency of angular velocity error is determined by the maximum thermal heat flux. The proposed method is useful for forecasting the temperature distribution of the spacecraft manipulator system, and will provide meaningful information for performance enhancement of the aerospace facilities.

An approach to system reliability prediction for mechanical equipment using fuzzy reasoning Petri net

Reliability prediction is a critical process of conceptual design for one evolutionary system when it has not been physically built. Due to the limitation of operation data, during the early stage of design, the reliability of a new product is difficult to predict, especially for complex mechanical systems. This article introduces a new method to predict reliability in the early stage of design phase, which uses fuzzy reasoning Petri net to generate the three values, representing complexity, importance and quality of subsystems for the product count reliability prediction. This approach solves the problems of data deficiency and high complexity in the existing methods. The effectiveness and advantages of the proposed method are validated by a case study of a real mechanical system of the spacecraft solar array. The analysis results show that this new method is able to reach an accurate predicted failure rate compared with the reported lifetime of the solar arrays.

Erection mechanism of glossal hairs during honeybee feeding

Many animals use their mouthparts or tongue to feed themselves rapidly and efficiently. Honeybees have evolved specialized tongues to collect nectar from flowers. Nectar-intake movements consist of rapid protraction and retraction of glossa from a tube formed by the maxillae and labial palps. We establish a physical model to reveal the driving mechanism of hair erection. Results indicate that the glossa of honeybees is similar to a compression spring. Experimental results show that hair erection is generated by the tension of hyaline rod and the elasticity of segmental sheath. The retractor muscle of hyaline rod is contracted at first, which compresses the sheath of pigmented rings and flattens the hairs. While the retractor muscle of hyaline rod relaxes, the elastic energy storage in the compressed glossal sheath will release to change the equivalent stiffness of glossal sheath and erect glossal hairs. These results explain the erection mechanism of glossal hairs during honeybee feeding.

In-Plane Free Vibrations of an Inclined Taut Cable

The investigation of the free vibrations of inclined taut cables has been a significant subject due to their wide applications in various engineering fields. For this subject, accurate analytical expression for the natural modes and the natural frequencies is of great importance. In this paper, the free vibration of an inclined taut cable is further investigated by accounting for the factor of the weight component parallel to the cable chord. Two coupled linear differential equations describing two-dimensional in-plane motion of the cable are derived based on Newton’s law. By variable substitution, the equation of the transverse motion becomes a Bessel equation of zero order when the equation of longitudinal motion is ignored. Solving the Bessel equation with the given boundary conditions, a set of explicit formulae is presented, which is more accurate for determining the natural frequencies and the modal shapes of an inclined taut cable. The accuracy of the proposed formulae is validated by numerical results obtained by the Galerkin method. The influences of two characteristic parameters and on the natural frequencies and modal shapes of an inclined taut cable are studied. The results are discussed and compared with those of other literatures. It appears that the present theory has an advantage over others in the aspect of accuracy, and may be used as a base for the correct analysis of linear and nonlinear dynamics of cable structures. DOI: 10.1115/1.4003397 Cables are promising structural elements in engineering applications because of their high flexibility, light weight, and high packaging efficiency. They are widely used in many mechanical systems and civil structures. A thorough and exact analysis of cable dynamics is of great importance for the design of cable structures, among which the derivation of accurate analytical expressions for the natural modes and the natural frequencies of taut cables is particularly important. The main advantage of having these expressions is that the influence of the cable principal parameters can be studied clearly. Other advantages include that the correct calculation of natural frequencies and modal shapes can be obtained, and the expressions can be used as the bases for nonlinear dynamics analysis. The linear theory on free vibrations of suspended taut cables supported at both ends has been developed for a long time. Through different methods, such as Newton’s laws, Hamilton’s principle, or the finite element method, various kinds of cable motion equations had been built and then linearized based on small amplitude assumption. These works could well demonstrate the vibration characteristics of a suspended small-sag cable with two supports located at the same level. However, for the case of an inclined cable, namely, one support is some distance below the other, most of the research tended to ignore the weight component parallel to the cable chord to simplify the analysis, which often led to inaccuracy in the definition of static profiles of suspended inclined taut cables and in the derivation process of governing differential equations.

Energy saving strategies of honeybees in dipping nectar.

The honeybee’s drinking process has generally been simplified because of its high speed and small scale. In this study, we clearly observed the drinking cycle of the Italian honeybee using a specially designed high-speed camera system. We analysed the pattern of glossal hair erection and the movement kinematics of the protracting tongue (glossa). Results showed that the honeybee used two special protraction strategies to save energy. First, the glossal hairs remain adpressed until the end of the protraction, which indicates that the hydraulic resistance is reduced to less than 1/3 of that in the case if the hairs remain erect. Second, the glossa protracts with a specific velocity profile and we quantitatively demonstrated that this moving strategy helps reduce the total energy needed for protraction compared with the typical form of protraction with constant acceleration and deceleration. These findings suggest effective methods to optimise the control policies employed by next-generation microfluidic pumps.