Precise positioning and control of the most popula

2022-08-04
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Precise positioning and control of NC chain tool magazine the chain structure of chain tool magazine determines that there are obvious defects in the tool magazine itself: poor mechanical rigidity and large transmission clearance, resulting in poor positioning accuracy of the tool magazine and often causing machine tool failures. The sdl120 NC chain tool magazine developed by our factory adopts analog electronic inspection and control circuit, which solves the problem of fast and accurate positioning of chain tool magazine

sdl120 main parameters of NC chain tool magazine: the tool capacity is 120; Tool taper is iso50; The maximum tool diameter is 250mm; The maximum market supervision length of the tool is 500mm

sdl120 CNC chain tool magazine is mainly composed of worm gear reducer, chain tool storage bin, manipulator shuttle device and manipulator. The chain storage bin of the tool magazine is driven by the servo motor through the cylindrical worm reducer, and the position ring is open-loop controlled. The tool base of the storage bin relies on the encoder to decode the tool number, and the accurate positioning is completed by the analog electronic inspection and control circuit (Fig. 1)

figure 1

the functions of each part are briefly described as follows

1. There are 120 cutter bases on the chain and cutter base, which are used to store 120 cutters. The whole chain is driven by servo motor

2. The distance between the output voltage (or current) of analog proximity switch and the object and proximity switch has a wide and accurate loading speed and test force range, which is approximately linear. As the tool handle of the tool is a circular structure, and the two proximity switches are installed in parallel, when the moving tool handle passes through the two proximity switches in a certain direction with the rotation of the chain, the two proximity switches each output a voltage signal with an approximate sinusoidal law, and there is a phase difference between the two signals, as shown in Figure 2

figure 2

3 The comparison circuit compares the two analog voltage signals and makes the following judgment: if the output comparison result reaches the positive maximum value first, the tool magazine chain rotates in the positive direction; When the output comparison result reaches the negative maximum value first, the tool magazine chain rotates in reverse; If the output comparison result is converted from the positive and negative maximum value to "0", the tool holder is located in the middle of the two proximity switches, that is, the accurate positioning position of the tool magazine. The positioning accuracy of the tool holder can be adjusted by adjusting the threshold value of the zero position window. If the window value is too large, the positioning accuracy is low. If the window value is too small, the tool magazine chain jitters and positioning cannot be completed. This is the reason why closed-loop control is not used

4. Logic processing circuit logic processing circuit is the core of tool magazine positioning control. It mainly completes the following functions: calculating the best tool finding path; Control the forward and reverse rotation and start and stop of the chain; Quickly find the precise positioning area of the required tool holder; Control precise positioning and output positioning completion signal

5. The communication interface circuit is used for information exchange between the logic processing circuit and the machine tool PLC. For example, the tool finding command, positioning command, tool grasping command, tool releasing command, manipulator control command and required tool number given by the machine tool PLC. The logic unit provides positioning completion signal, tool holder with tool signal, manipulator in place signal, etc

6. The manual control circuit is mainly used by the operator for tool replacement, adjustment, production commissioning and machine tool maintenance

7. The given circuit converts the signal of the given limit pin from the logic control circuit, which is composed of a conical plug and a connecting rod, and the given signal of the manual control circuit, which has an approximate conversion relationship between the hardness value of the given material and the tensile strength value, into the given signal required by the servo drive

8. The servo drive circuit and motor are used to drive the rotation of the magazine chain. We selected Siemens 611A series servo system and its corresponding motor

see Figure 3 for tool change process control

figure 3

the above control schemes have been applied and verified in the numerical control machine tool major240 produced by our factory. The longest tool change time (tool change of spindle right angle milling head with tool) does not exceed 30s, and it is stable and reliable. It greatly shortens the non processing working hours, improves the processing efficiency, meets the needs of the market, and improves the level of domestic processing centers. (end)

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