As one of the economic forest fruits with Chinese characteristics, jujube has the largest planting area and yield in the world [
1,
2]. With its superior geographical location and climatic conditions, Xinjiang has developed into the largest planting district for jujube trees in China [
3,
4]. As one of the important steps in the management of jujube gardens, the pruning of jujube trees mainly relies on manual pruning by jujube farmers [
5]. By 2020, the area planted in jujube trees in Xinjiang was about 445,225 hm
2, and the output was up to 3,727,729 t [
6]. However, the problems of poor operating conditions, high labor intensity and low efficiency are significant [
7,
8,
9]. Therefore, research on and development of machines or tools for mechanized pruning is an inevitable trend for the sustainable and healthy development of the jujube industry.
At present, the methods of pruning fruit trees mainly include artificial pruning and mechanical pruning [
10,
11,
12,
13,
14]. In artificial pruning, fruit farmers prune the fruit trees with simple auxiliary pruning tools. Commonly used auxiliary tools include manual, electric, pneumatic and hydraulic scissors [
15,
16]. Among them, manual scissors have the shortcomings of labor intensity, low work efficiency and easily caused occupational diseases; Electric, pneumatic and hydraulic scissors need to be equipped with a power source, whose weight makes them unsuitable for manpower to operate for long periods [
17,
18,
19]. Mechanical pruning mainly uses a pruning machine to conduct shaping and pruning on a large scale and in orchards with standardized planting patterns [
20]. At present, the common pruning machines for fruit trees are composed of a pruning device, frame, power system and other key components [
21,
22]. The design of a pruning machine involves the design of key components of the pruning device, including the design and selection of the structure and working parameters of the tool. According to the working mode, the commonly used pruning devices include reciprocating moving cutters and disc cutters [
23,
24,
25]. Recently, many studies have been conducted on mechanized pruning equipment for horticultural plants or orchards at home and abroad [
26,
27,
28]. In 1955, Moore et al. in America developed a saw-disc pruning machine to reduce the cost of pruning citrus trees by hand [
29]. Its pruning device was composed of 12 sets of disc cutters, which could achieve unilateral pruning of fruit trees with a pruning efficiency of 0.4 hm
2/h. However, this machine could prune one side of the trees, but could not complete the shaping and pruning of a single plant; the pruning form was single, and the adaptability was poor. Based on the growth characteristics of fruit trees such as grapes, apples and pears, Poni et al. introduced the curtain pruning machine to cut upright growing branches, which improved the efficiency of pruning [
30]. Spinelli et al. in Italy designed a pruning machine for olive trees, which was mainly composed of a pruning device and crushing and recycling mechanism for residual branches. This machine can crush and recycle residual branches while pruning olive trees, but can only prune one side of the tree [
31]. In 2014, Xinjiang Agricultural University designed a single-side reciprocating pruning device for grapes to solve the problem of high cost and low efficiency of manual vineyard pruning [
32]. It was composed of a frame, pruning device, power system, copying frame, etc. The machine had an operating speed of 0.8 m/s, cutting height of 30 mm, cutter stroke of 76 mm, a simple structure, and high efficiency, but had the shortcomings of poor robustness and easy clogging. In 2015, Shihezi University developed a pruning machine for grapevines [
33], which pruned the tops and sides of grapevines with a disc cutter; it was suitable for cutting thinner branches of the grapevines. In 2016, Shandong Agricultural Machinery Research Institute designed the PJS-1 two-wing pruning machine for grapes [
34], which consisted of a frame, a trimming device, a transmission system and a hydraulic system. The machine controlled its tool speed through the hydraulic system, had an operating speed of 5–7.5 km/h, pruning width of 1400–2400 mm, and pruning height of 400–2000 mm, and could complete pruning of the left and right sides and top branches of the grapes in one operation. In 2019, Huazhong Agricultural University designed a pruning machine for citrus, consisting of a frame, a transmission device, a space track moving device, an actuator for the pruning arm, a hydraulic actuator, and a walking suspension device. The maximum missed pruning rate of the machine was 10.1%, and the qualified rate was 88% [
35]. In 2020, Xinjiang Agricultural University designed a single-motor reciprocating pruning machine for grapes [
36], which used a single hydraulic motor to drive a reciprocating cutter to prune single sides and tops of grapevines at the same time, with a cutting speed of 1.66 m/s, feeding speed of 1.46 m/s, clean grape stalk cutting rate of 90.66%, and stubble breakage rate of 4.71%. In 2020, Liu et al. designed a wideband combination copying pruning machine for new orchards [
37] comprising a frame structure, cutting device, transmission system and hydraulic system. The cutting height range of the machine was 500–4000 mm, the maximum cutting diameter was 60 mm, the missed rate of pruning was 7.3%, and the qualified rate of pruning was 90.9%. The quality of the cut section and the shape of the cut met the requirements for agronomic application. In 2021, Li et al. designed a form trimming machine for horticultural plants [
38], the pruning device of which consists of multiple cutting tools that move back and forth. It takes about 8.89 s to trim a single horticultural plant with this machine. Anhui Academy of Agricultural Sciences designed a pruning machine for mulberry, which includes a transmission device, a hydraulic actuator, an actuator for the pruning arm, a space track moving device, and a walking suspension device. The maximum missed pruning rate of this machine is 10%, and the qualified rate is 90% [
39]. At present, the design of and research on shaping and pruning machines by domestic and foreign researchers is mainly aimed at horticultural plants with soft branches and easily broken stalks, such as vines. The cutting parts of most pruning machines use low speed reciprocating cutting tools. Due to great differences in growing information and agronomic pruning requirements for different varieties of fruit trees, existing shaping and pruning machines for fruit trees cannot meet the intensive pruning requirements for large-scale orchards of dwarf and densely planted jujube trees with hard branches.
To sum up, a shaping and pruning machine that is connected with a tractor by the front suspension was designed for jujube trees to meet the demand for mechanized and rapid shaping and pruning of dwarf and densely planted jujube trees in Xinjiang. Firstly, according to the growth information and agronomic pruning requirements of jujube trees, the pruning device was designed with a structure consisting mainly of a number of high-speed rotating cutters. Additionally, a mathematical model for avoiding missed cuttings with the cutter was established on the basis of a theoretical analysis of the movement path of the cutting tool in the process of cutting jujube branches. Meanwhile, the structure and working parameters of the removal mechanism for jujube hangings and the shaping frame were designed. Secondly, utilizing the forward speed of the machine, cutter rotation speed, and cutter diameter as influencing variables and the missed pruning rate and stubble breakage rate as evaluation indexes, a quadratic regression orthogonal test with three factors and three levels was constructed. Then, the prototype was produced, and a field pruning test was carried out. The mathematical regression model of influencing factors and evaluation indexes was established through analysis of variance and response surface analysis of test results. Finally, the best parameter combination of experimental factors was selected according to the model analysis results to carry out field validation tests. This study aimed to improve jujube tree pruning efficiency and reduce jujube garden management costs. The results could provide technical support for promoting the complete mechanization of jujube garden management.