TPT May 2013

Article

Now also for the most demanding hydraulic tasks Already since version 3.2 of S7-Technology, the hydraulic functions of the technology CPU have been successively expanded. Since then, there is a technology template for automatically recording the hydraulic characteristic curve “GetCharacteristics”. The non-linear characteristic curve of the track (Figure 3) is recorded by the tool and transferred to the technology processor. Based on this information, the technology firmware can balance non-linear tracks and dead zones. The result is a reproducible control response with high control quality. In this way, less complex proportional directional control valves can be used in many cases instead of more expensive servo valves. Ebm has used this characteristic curve tool and was able to use it to transfer the defined cam disc for linearisation directly to valves of the same type without further adaptation. In version 4.2, there are new hydraulic functions (pressure control and pressure limiting), where it is possible to make a switch on the fly between position and pressure control (and vice versa).

In addition, the T-CPU now also supports differential pressure measurements, the switchover between different sensors (eg several actual pressure values), and the implementation of individual pressure profiles. Thus, everything that Ebm machines need. With all of this, the user has absolute freedom and can precisely and flexibly adapt the controller to the respective requirements – with the well-known resources of the Simatic world, without proprietary software for programming and operating. In addition, the engineering overhead for communication between the PLC and the hydraulic controller is eliminated and the software maintenance is simplified. Figure 2 : Interacting with an IM174 interface module (right), the Technology CPU Simatic S7315T2 DP coordinates the four hydraulic axes of the machine for analogue value/encoder signal processing. Pressure cells are integrated via fast analogue inputs ET200S HF (left) Ebm first used the expanded capabilities of the hydraulic control of the technology CPU on the standard machine IO902 (Inside/Outside), with two processing units for pipes with outer diameters up to 90mm. On both units, pipe ends can be shaped and calibrated with extreme precision, both from the inside (eg via conical mandrels) and from the outside (eg via segmented annular shells). The four-axis machine was available to replace the hydraulic controller that was previously used in addition to a Simatic PLC with an integrated solution on the basis of a technology CPU S7315T2 DP with expanded hydraulic functionality. Designed for four axes and thus tailored to the IO902, there is also the IM174 interface module, an isochronous Profibus module. This converts the setpoints calculated by the position controller of the technology CPU and outputs it to the analogue setpoint interface (±10 V) of the proportional directional control valves. Ebm records the actual positions of the hydraulic axes via SSI encoders and feeds them back to the CPU via the IM174. Alternatively, this could also be done directly via the isochronous Profibus or via ET200S/ET200M modules. Via fast input/output modules (HF/High-Feature) from the Simatic ET200S line, pressure cells are connected to the pressure controller of the technology processor, in order to record and control (tool protection) the shaping pressure (here, a maximum of 120 bar, generally up to 250 bar). Quickly together to the first application

Figure 1 : The first application of the Simatic Technology CPU with expanded hydraulic functions at Ebm is the IO90-2 pipe end processing machine

110

www.read-tpt.com

May 2013