Jizhan Liu

Effect of tomato internal structure on its mechanical properties and degree of mechanical damage

As different tomatoes have different locular cavities and a particular tomato material is inhomogeneous, the effect of tomato internal structure on its mechanical properties and degree of mechanical damage may be significant during the gripping process with robot fingers. This was studied using the loading-unloading experiment as well as the observation of shelf life. The results showed that the plastic strain energy, Ep, peak force, Fmax and degree of elasticity, rc, were not significantly affected by the internal structure of three-locular tomato before its failure, but loading slope, rk, was. The degree of elasticity, rc and loading slope, rk, were significantly affected by the internal structure of four-locular tomato before its failure, but the plastic strain energy, Ep, and peak force, Fmax, were not. The compressibility e was the most important explanatory variable in the model of the degree of mechanical damage to tomato. The internal structure of four-locular tomato had a significant effect on its degree of mechanical damage, but the internal structure of three-locular tomato does not. Excluding the covariates, at the same compressibility, the degree of mechanical damage was greatest under the condition of F*CW and lowest for F*L their difference was 21.3%. The discrepancy of the medium degree of mechanical damage was slight under the condition of T*CW and T*L, respectively.

Fruit biomechanics based on anatomy: a review

Abstract Fruit biomechanics is needed for quality determination, multiscale modelling and engineering design of fruit processes and equipments. However, these determined fruit biomechanics data often have obvious differences for the same fruit or tissue. In order to investigate it, the fruit biomechanics based on anatomy was reviewed in this paper. First, the anatomical characteristics of fruit biomaterials were described at the macroscopic ‘tissue’ level and microscopic ‘cellular’ level. Subsequently, the factors affecting fruit biomechanics based on anatomy and the relationships between fruit biomechanics, texture and mechanical damage were summarised according to the published literature. Fruit biomechanics is mainly affected by size, number and arrangement of cells, quantity and volume of intracellular spaces, structure, thickness, chemical composition and permeability of cell walls, and pectin degradation level and turgor pressure within cells based on microanatomy. Four test methods and partial determined results of fruit biomechanics were listed and reviewed. The determined mechanical properties data of fruit are only approximate values by using the existing four test methods, owing to the fruit biomaterials being non-homogeneous and living. Lastly, further aspects for research on fruit biomechanics were proposed for the future.

Analysis of Workspace and Kinematics for a Tomato Harvesting Robot

Firstly, a tomato harvesting robot in greenhouse is introduced, the workspace of which is visually verified that it covers the tomatoes distribution space of one plant and hasnpsilat cavity by the pose diagrams of end-effector, and the designed robot has high flexibility. Subsequently the forward and inverse kinematics of harvesting robot is analyzed, so the range of joint variables and the inverse solution are obtained, and the catastrophe problem of robot joint value is solved with the arithmetic application of numerical value comparison. Finally the kinematics of harvesting robot was simulated by using the Robotics Toolbox in Matlab on the workspace, and results indicate the parameters of the designed end-effector are rational, and this end-effector can work well with manipulator. So the harvesting robot can meet the working requirement in greenhouse.

Hand-arm coordination for a tomato harvesting robot based on commercial manipulator

An executive system of tomato harvesting robot was constructed by integrating self-designed end-effector with commercial Motoman manipulator. To communicate the enclosed controller JRC of manipulator with PMAC controller of end-effector, statements in programs of both PComm32PRO and WINCAPS were used to set digital input/output by each other through two relays and certain condition judging statements in programs were monitor. Alternating and composite coordinative control modes were both realized with this method. Experiment results indicated that success rate of harvesting for alternating mode and composite mode were 70.0% and 83.3%, respectively. Average cycle time for alternative mode was 6.2 sec, compared with 6.0 sec for composite mode. Feasibility of hand-arm coordination based on commercial manipulator was proved, while highly integration of the control system need to be focused in further research.

Design of a laser stem-cutting device for harvesting robot

Since traditional detaching methods have shortfalls in practice, a laser stem-cutting device for fruit harvesting robot was designed, which includes a laser generation and control unit and an actuating mechanism. A 30 W high-power fiber-coupled laser diode is selected, and it is supplied with a lithium battery whose gradually-dropped voltage is turned to constant-current by a constant-current supply circuit. In the protection/control circuit, two-step slow start of the laser diode is achieved by a RC delay circuit and a delay relay circuit. To cut stems off, the focusing lens installed on the end-effector of harvesting robot and connected with the laser by a fiber is driven by a Maxon mini DC motor through a bearing structure. Experiments indicate that this device works well and effectively.

Identification of road surface conditions based on laser scanning

Detection water and aqueous land hazards in outdoor navigation is a big challenge in unknown outdoor environment. Advantages of laser scanning are encouraging, firstly due to its distinguished detection capacity at night and less quantity of data. It was found by experiments that there was no evident changing trend of laser remission with the increase of color density in water, no matter green, red, or dark blue. These colored water shared common feature of weak mirror-deflection with pure water. However, remission of black water surface dropped linearly approximately with the increase of color density, and strong mirror-deflection was observed. Experiments also indicated that water turbidity had great effect on both remission and mirror-deflection, and there was significant positive correlation between laser remission and the soil moisture content. These phenomena could be explained with twice reflected pulse property of laser range finder and optical property of water-air interface in laser scanning. Based on the experiment results, methods to distinguish pure or turbid water surface from land and to distinguish hazard aqueous land from safe dry land in natural scene were put forward.