What factors are related to the processing accuracy of automatic dispensing machines?
Release time:
2023-04-04
Source:
When purchasing an automatic dispensing machine, we often see a parameter that repeats the positioning accuracy. Sometimes, the XY and Z axes are marked separately, ranging from 0.1 to 0.001mm accuracy. What factors are related to this positioning accuracy?
We know that the dispensing valve is fixed on the dispensing head, and the dispensing displacement is executed by the machine. Therefore, the dispensing positioning accuracy is only related to the motion execution of the machine, that is, the driving accuracy of the XYZ axis. CCD vision, needle, etc. belong to auxiliary positioning modes, and fundamentally have little impact on the dispensing positioning accuracy.
The common shaft drive method is motor drive. The positioning operation is driven by tracks or gears. Different types of motors achieve different positioning accuracy.
Automatic dispensing operation requires at least millimeter level positioning accuracy, so ordinary three-phase motors cannot meet the usage requirements. Most dispensing processes also require micrometer level dispensing accuracy, so servo motor closed-loop control driving mode has become mainstream. For automatic dispensing machines, in order to improve accuracy requirements, precision screws are generally used in conjunction with transmission positioning. Different combinations can achieve different repeated positioning accuracy:
1. Driven by precision grinding screw and closed-loop stepper motor, limited by the torque of the stepper motor. Desktop dispensing machines are widely used and can achieve repeated positioning accuracy of ± 0.02mm;
2. The precision grinding rod is driven by a closed-loop servo motor, with slightly higher accuracy than a stepper motor. The mainstream automatic dispensing machine adopts this scheme, which can achieve a repeated positioning accuracy of ± 0.01mm; Of course, the accuracy of servo motors varies depending on the size of the load and the applicable situation. For servo motors in the low-speed range, the positioning accuracy can also reach ± 0.005mm;
3. Magnetic levitation direct drive linear motor, with further improvement in accuracy, generally adopts high-precision automatic dispensing machine, with a repeated positioning accuracy of ± 0.005mm, basically covering the vast majority of high-precision dispensing requirements. This is also a cost-effective shaft control scheme.
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