固定式割胶机器人割胶误差分析与精度控制

针对固定式自动割胶设备成本高、质量大和割胶精度低等问题,该研究提出一种采用高分子材料制作的固定式割胶机器人,提出一种先扫描后切割的割胶控制方式。利用超声波传感器预先扫描树围,通过建立测量误差控制模型得到刀尖与树皮的距离,利用PID控制算法控制刀具进给量。为减少进退刀次数和降低电机功率损耗,根据橡胶树皮结构和割胶技术规程,将切割深度从5.5 mm调整为5.2~5.8 mm,并进行试验验证。结果表明:固定式割胶机器人割胶时螺旋角为25°~30°,其控制方式可保证刀尖到达目标位置,且1次走刀即可完成割胶工作,有效切割时间仅为22 s,相比于传统人工割胶(需多次走刀,有效切割时间为1 min),该割胶机器人的割胶效率提高了63%,可实现快速精准割胶。在固定的切割深度范围内作业时,进退刀次数减少36%;刀具电流变化幅度最大减小4.11%。该研究设计的固定式割胶机器人及控制方式不损伤橡胶树,可替代人工作业,提高割胶效率,具有一定的推广应用价值。

Tapping error analysis and precision control of fixed tapping robot

Abstract: Tapping is the key technical procedure for the extraction of the latex from rubber trees in the processing of natural rubber. However, there are some problems of current fixed rubber-tapping equipment, such as high production cost, high weight of the whole machine, and low tapping precision. In this study, a new fixed tapping robot was designed using the advanced polymer materials. The tapping robot was mainly composed of the clamping mechanism, tapping table, combined roller screw pair, and the module of measuring limits. The weight of the main body in a robot was reduced, thereby to make it easier assemble than before. It is conducive to mass processing and production of tapping robots made of polymer materials, due mainly to the processing cost was also reduced. Specifically, the clamping component was utilized to hold on the tree trunk, when the tapping robot was attached to the rubber tree within the rubber cutting cycle. A tapping control system was selected to scan the tree rounds before tapping. In processing, the eccentric load can cause the bending behavior of rubber trunk between tapping robot and the tree trunk. A circumferential motor and an axial motor were set to control the trajectory of cutter. The running speed of two motors was controlled to move at a certain ratio during the cutting process, where the spiral secant in space was formed from the bottom right to the top left around the rubber tree. An ultrasonic sensor was used to scan the tree rounds, thereby to determine the distance between the ultrasonic sensor and rubber trunk. A mathematical model of error predictive control was established to obtain the distance between the tip of the cutter and the bark. A PID control was also selected to control the cutter feed, thereby to reduce the cutting error in rubber tapping. The range of cutting depth was determined, according to the structure of rubber bark, and the relevant technical regulations for tapping. The fixed cutting depth of 5.5 mm was expanded to the range of 5.2 to 5.8 mm, in order to reduce the counting of the cutter moving forward and backward, while reduce the power loss of the motors. Taking the rubber tree with the trunk diameter of 180 mm as a research material, a rubber cutting test was conducted to verify the simulation data, where the cutting helix angle was set as 25° in tapping. The results showed that the cutter tip of a tapping robot was guaranteed to reach the target position through the control system. The tapping work was completed by one pass, where the effective cutting time was only 22 s. The tapping efficiency of a fixed tapping robot increased by 63%, compared with traditional manual tapping, where usually multiple passes were required and the effective cutting time was 1 min. The fixed tapping robot achieved the fast and accurate tapping. The bark consumption of cutting rubber was 1.1 mm, indicating suitable for the requirement of bark consumption in the technical specification of tapping. The counting of the cutter moving forward and backward was 36%, lower than that of the original scheme during tapping within the range of 5.2-5.8 mm cutting depth, and the maximum variation range of cutter current was reduced by 4.11%. The rubber tree was not damaged by means of the fixed tapping robot and tapping control. The fixed tapping robot can be expected to completely replace the manual tapping, and further widely popularize due to its reduced motor power, and improved tapping efficiency.