Key technology for plastic pipe production

When plastic pipes are in production, these can be cut according to the required lengths. During the cutting process, there is a need for cutting trolley synchronized with the production line speed, where strict synchronization is demanded. This is to ensure smooth pipe cutting and durability of cutting tool and the synchromesh mechanism. In the controlled synchronous mode, what is mostly adopted is speed regulator which is between cutting trolley and upstream hauling caterpillar to establish a certain proportionate relationship according to the inherent mechanical transmission ratio. But one of the biggest disadvantages of this scheme is the line speed which feedbacks from hauling inverter and is not the actual pipe forward speed. So even if the cutting trolley's movement adopts the very accurate follow-up method, it might cause synchronism deviation because of the erroneous master controls. 

For the design of its new series of swarfless cutting unit, Liansu has adopted the encoding wheel (coaxial connected with encoder) which is directly in contact with pipe surface being the main, while the servo motor which drives cutting trolley acts as support. The important point here is that the synchronization calculation of the main and the support which uses the following electronic cam method during the cutting process results in the cutting trolley strictly synchronously following the line speed of pipes.  

First, the speed data collected from the encoding wheel can reflect the real pipe forward speed; second, the cutting trolley is driven by servo motor, and the servo motor drives 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 achieved a very good synchronization condition. [llustration 1]

In Illustration 2 on the stage of Ls1, the cutting unit just got the fixed-length cutting signal, within the specified length of Ls1, and this enables the static state to reach the line speed Vy fast. Only upon completely reaching line speed Vy, the cutting machine can clamp and cut the pipe. Folloing the process of cutting feed, which is at AL synchronous follow area, the cutting trolley must strictly follow the encoding wheel's speed (line speed). In this area, cutting trolley's movement is synchronized, even if the line speed changes.

       Illustration 1

Synchronization precision brings advantages  

This precision in synchronization can bring the following advantages:

First: During the cutting process (AL area), cutting blade and pipes is relatively static. This is a great help in improving incision's quality, which will greatly improve the durability of clamping device and synchronous movement device.

Second: In terms of length deviation in fixed-length cutting, generally is + / — 5 mm. Actually, the main reason of length error is not mainly from encoding wheel's measurement error, but in cutting length signal transmission to the clamping mechanism which completely clamped the pipe surface, and this period of time is unpredictable (since the traveled distance of encoding wheel is unpredictable). It is also easy to operate since after the pipe is clamped, the cutting trolley will have active or passive movement. As long as there is enough clamping force, pipe surface and the cutting blade will see no relative movement. Therefore, after clamping, no length error is generated. In the E-CAM control, Ls1 is set in the HMI since the servo system has good dynamic response function under the control of the E-CAM. Once the servo motor gets the length reached signal, the cutting trolley achieves the pipe line speed Vy in time with a specified distance of Ls1, thus actively synchronizing with line speed (not relying on clamping force passive synchronization). Therefore, it can reach very accurate cutting length accuracy + / - 0.5 mm (with minimal error collected from encoding wheel).

         Illustration 2

Third: This software can also visually reflect the cutting device to enhance the speed of the whole line, the operator or manager can accurately get the inverse relation V = a/T between cutting time and line speed to facilitate the analysis of line speed for different pipe size. From the Illustration 2: the Ls = Ls1 + A L + Ls2, general Ls1 = Ls2 = 20 mm, Ls is screw effective length, A 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 soon 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, we can also intuitively read the shortest pipe length which can be cut under the current line speed Vy. To know the shortest cutting length, set the length in waiting area L0 as "0". At present time, the shortest cutting length is 40+(3Ls-120)/S0/T+ Lb0. With Lb0=Ls, the shortest cutting length =80+(3Ls-120)/25/T. With this calculation formula, there will be E-CAM operation showing on the HMI.

Fifth: From the yellow area of Illustration 2, after cutting is finished, the cutting unit will quickly return to the middle stroke according to line speed, and then gradually decelerate until it stops to origin position. The returning speed is automatically adjusted according to production line's speed, which can effectively ensure the rapid return and stability, and avoid the fast return impact while in high-speed production, to greatly improve the durability of mechanical parts.

        Illustration 3

Sixth: Illustration 3 shows the parameter interface of HMI of swarfless cutting unit, when the accurate related mechanical and electrical parameters have been included in the settings. Regardless of configuring the production line from any third party, there is no need 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. (Drawing III).

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