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Key technology for plastic pipe swarfless cutter: synchronous accuracy.

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Principle description:

      When plastic pipe online production, it can be cut off according to our required fixed-length. In the cutting process, requires cutting trolley synchronized with production line speed, only in the case of strict synchronization, in order to ensure the smooth pipe cuts and the durability of cutting tool and the synchromesh mechanism. In the control mode of synchronous, mostly adopt speed regulator which between cutting trolley and upstream hauling caterpillar to establish a certain proportion relationship according to inherent mechanical transmission ratio, one of the biggest disadvantage of this scheme is the line speed which feedback from hauling inverter is not the actual pipe forward speed, even if the cutting trolley's movement adopts the very accurate follow-up method, it might cause synchronism deviation because of the master controls mistake.  

     For the design of new series swarfless cutting unit, Liansu adopt the encoding wheel (coaxial connected with encoder) which directly contact pipe surface as “master”, the servo motor which driven the cutting trolley as “slaver”. The important is, the synchronization calculation of “Master” and “Slaver” which use the following electronic cam method, during the cutting process, the cutting trolley strictly synchronously follow the line speed of pipe. Hardware configuration is as Drawing 1:

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1. Linear speed encoding wheel; 2. Communication system   3. E-CAM synchronous controller; 4. Servo motor; 5. Gear; 6. Rack 

(Drawing 1)

        First, the speed data collected from the encoding wheel can be reflected the real pipe forward speed; second, cutting trolley driven by servo motor, and the servo motor drive the gear to move on the rack, to guarantee it will make a quick response according to the master control. For the hardware configuration, it has already have a very good synchronization condition. From below Drawing 2 the analysis of “the master” & “the slaver” synchronization process (it's done by Liansu's E-CAM synchronous controller).

 

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(Drawing 2)

       From Drawing 2, in the stage of Ls1, the cutting unit just got the fixed-length cutting signal, within the specified length of Ls1,fast from the static state reached the line speed Vy, only completely reach line speed Vy, the cutting machine can clamp and cut the pipe.In the following process of cutting feed, which is at △L synchronous follow area, cutting trolley must strictly follow the encoding wheel's speed (line speed).In this area,cutting trolley's movement is synchronized with it, even if the linear velocity changes.

Synchronization precision bring advantages for plastic pipe cutting:
    First: During the cutting process (△L area), cutting blade and pipes is relatively static.This is a great help for improving incision's quality, which will greatly improve the durability of clamping device and synchronous movement device.
    Second: In terms of fixed-length cutting length deviation, generally is ±5 mm. Actually, main reason of length error, its not mainly from encoding wheel's measuring error, but rather in cutting length signal transmission to the clamping mechanism completely clamped the pipe surface, and this period of time is unpredictable (cause the encoding wheel distance traveled unpredictable). It is easy to understand: after pipe clamped, cutting trolley will have active or passive movement, as long as enough clamping force, pipe surface and the cutting knife will be no relative movement. Therefore, after clamping, no length error is generated. In the E-CAM control, Ls1 is set in the HMI, due to the servo system has good dynamic response function, under the control of the E-CAM, once servo motor get the length reached signal, thus can ensure the cutting trolley reach the pipe linear velocity Vy in time with a specified distance of Ls1, thus actively synchronize with linear velocity (not rely on clamping force passive synchronization). Therefore can reach very accurate cutting length accuracy + / - 0.5 mm (tiny error just collected from encoding wheel).
     Third: This software also can visually reflected the cutting device can enhance the speed of whole line, the operator or manager can accurately get the inverse relation V = a/T between cutting time and line speed , facilitate the analysis of line speed for different pipe size. From the Drawing 2: the Ls = Ls1 + △ L + Ls2, general Ls1 = Ls2 = 20 mm, Ls is screw effective length, △ L = Vy * T (T is total cutting time ), as a result, Ls = 40 + Vy * T, namely Vy = (Ls - 40)/T, among them, Vy unit is mm/s, Ls unit is mm, T unit is s, if change Vy unit into m/min, then Vy * 1000/60 = (Ls - 40)/T, namely Vy * T = (3 Ls - 120) / 50, from the formula, we clearly see, as far as we get the time of pipe cutting, we can easily calculate the max line speed the cutter can follow. 
     Fourth: from the control software, also can intuitively read the shortest pipe length which can be cut under the current line speed Vy, to know the shortest cutting length, only set the length in waiting area L0 as "0", at this time, the shortest cutting length is 40+(3Ls-120)/50/T+Lb0. Because Lb0=Ls, the shortest cutting length =80+(3Ls-120)/25/T, by this calculation formula, there will be E-CAM operation showing on the HMI.
     Fifth: From yellow area of Drawing 2, after finish cutting, the cutting unit will quickly return to the middle stroke according to line speed, then gradually decelerate until stop to origin position.The returning speed is automatically adjusted according to production line's speed, which can effectively ensure the rapid returning and stability, avoid the fast returning impact while high-speed production, to greatly improve the durability of mechanical parts.
     Sixth: Drawing 3 shows the parameter interface of HMI of swarfless cutting unit, when the accurate related mechanical and electrical parameters has been settings, regardless of configuring the production line from any third party, theres no necessary to connect the synchronizing signal with upstream haul-off unit and modify parameters, it can reach the purpose of accurately synchronizing with the line speed, which bring great convenience to the production and debugging.

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(Drawing 3)