Digging machine is a kind of digging and tillage machine. Because its structure is simple and it can be operated conveniently, it is widely used as a hole digger. There are mainly 4 types of digging machines, i.e. suspension type, portable type, traction type and self-propelled type. On the mountains, hills, ravines and other complex terrain conditions, portable type of digging machine is popularly used to dig a hole so as to plant or transplant trees. Hence, this paper designed a new portable digging machine with a half-nut mechanism to keep the feed rate stable and decrease the torque of the drilling bit as far as possible when drilling the hole. In addition, the support structure was also designed for the digging machine for the sake of guaranteeing the verticality of the hole and ensuring the reliability and stability of the digging machine, as well as making the structure more secure. The feed rate of the digging machine was an important factor, which affected the torque and work efficiency of the drilling bit greatly. Research on the effect of the feed rate on the dynamic mechanical parameters of digging machine was of great significance for developing a new model of digging machine. However, the power of the digging machine was gasoline engine, so the power output shaft could not reversely rotate, and it could not be used for actual digging. Thus there was a great need to design a new structure that could solve the gasoline engine's problem of rotating only in one direction. Accordingly, the half-nut mechanism was designed. According to the working principle of the half-nut, the motion characteristics of half-nut mechanism were analyzed by using the analytic method. The straight track angle of half-nut picks was decided as 105°, and thus a portable digging machine with half-nut mechanism was designed. The new designed digging machine could not only realize the digging operation automatically, but also complete the return movement rapidly. Then based on the working principle of digging machine, the relationship between the feed rate and the effect of lifting soil was studied. In order to verify the result, the experiment of testing the torque and rotational speed during the process of drilling a hole was conducted by using the torque measuring device JN338-100A made by Beijing Xinyuhang Century Science and Technology Co., Ltd. to collect the data afterward. Therefore it successfully provided a theoretical basis for the determination of feed rate of a new type of digging machine. It showed that when the pitch of half nut was taken as 3 or 5 mm, the torque and its fluctuation both were small. However when the pitch of half nut was taken as 8 mm, for it did not satisfy the working principle of digging machine, the torque and its fluctuation varied greatly, and the digging machine could not lift soil smoothly. In order to improve the work efficiency, the pitch of half nut was taken as 5 mm for this new designed digging mechanism finally. This paper provides a theoretical basis for the design of automatic feed mechanism of a new portable digging machine.%挖坑机钻头进给量是影响其扭矩和工作效率的重要因素,研究挖坑机进给量与其动态力学参数之间的变化规律对开发挖坑机具有重要意义.该文首先根据开合螺母的工作原理,利用解析法分析了开合螺母机构的运动特性,确定出了其动销轨道角为105°,进而设计出了一种开合螺母式自动进给机构的手提式挖坑机,不仅实现了挖坑作业的自动化,又能迅速完成回程运动.然后基于挖坑机升土理论,分析了挖坑机钻头进给量与其升土效果之间的影响关系,并通过试验进行了验证,从而为挖坑机进给量的设计提供了参考.研究表明,开合螺母螺距为5 mm时,挖坑机扭矩及其波动幅度均较小、工作效率最高.
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