Hydraulic control with Parker: pump drives, positioning and energy saving

Hydraulics still moves the heaviest loads in industry — presses, die-casting and injection-moulding machines, machine tools, test rigs. What has changed is the control around it. A pump that runs flat out all day and a cylinder positioned by limit switches waste energy, time and material. With modern electronics the same hydraulic system positions to a fraction of a millimetre, holds a pressure exactly and draws only the power the process actually needs. This article shows how Parker solves it on two levels — the pump and the axis — and which products from our range you need for each.

Two places where hydraulics gets smarter

Every hydraulic machine has a source of power (the pump with its motor) and consumers (cylinders and motors moved by valves). Electronic control pays off in both:

• At the pump a frequency inverter sets the pump speed so that it delivers exactly the flow or pressure the machine needs at that moment — instead of a constant-speed pump whose surplus oil is throttled away as heat.
• At the axis a controller closes the loop around position, force or pressure of each cylinder and drives the proportional or servo valve hundreds of times per second.

The pump: variable speed with the Parker AC30V

The Parker AC30V frequency inverter can run a dedicated hydraulic control application (Parker application RA502134U003, firmware 1.4.1 or newer). The inverter then is not just a motor speed controller — it becomes the controller of the hydraulic power unit itself. Flow is entered in L/min, pressure in kPa and the pump displacement in litres per revolution; the drive works out the speed. Four control modes cover the typical hydraulic circuits:

• Accumulator control — keeps an accumulator charged between a low and a high pressure limit, taken either from two pressure switches or from a pressure transducer. When the pressure falls, the drive adds flow (adjustable Q-compensation with delay, ramp and maximum).
• VFPC control (variable flow, pressure compensated) — for pumps with a mechanical pressure compensator: the drive follows a flow transducer and keeps an adjustable flow reserve, so the pump turns only as fast as needed.
• “Q” control — open-loop flow control: the drive converts the requested flow into pump speed from the displacement per revolution. No flow sensor is needed.
• “P” control — closed-loop pressure control with a PID controller, a pressure setpoint and a pressure transducer, with compensation for the pump's static losses and its mechanical and volumetric efficiency.

The application also looks after the power unit: oil-level and oil-temperature inputs stop the drive after an adjustable delay, up to four skip-frequency bands keep the pump away from mechanical resonance, and the display shows pump speed, load, flow, pressure, the hydraulic status and the energy used in kWh. Analogue outputs report pump speed demand and pump load to the machine control; relays report “running” and “not tripped”.

Where the energy saving comes from

A constant-speed pump delivers its full flow even when the machine is waiting, holding a position or only needs a fraction of the flow. The surplus goes back to the tank over a relief or throttle valve and turns into heat — which then has to be cooled away again. A variable-speed pump drive reduces the speed in exactly those phases: in hold and idle the pump turns slowly or stops, during a fast stroke it speeds up. The machine gets the same hydraulic performance with less electrical energy and less heat in the oil. How much you save depends on the duty cycle of the machine; the longer the pauses and partial-load phases, the bigger the effect.

The axis: closed-loop positioning with PAC120 and PACHC

For the cylinders themselves Parker offers a modular system that clips onto a 35 mm DIN rail in the control cabinet:

• PAC120 — the Parker Automation Controller for hydraulics. A compact controller with CODESYS V3.5 (IEC 61131-3), a real-time EtherCAT master, web visualisation and OPC UA, running Linux RT on a 1 GHz i.MX6 processor. It connects to the line or cell controller as a PROFINET IO/IRT slave (PAC120-PWP01), an EtherNet/IP adapter (PAC120-PWE01) or an EtherCAT slave (PAC120-PWT01); a CAN interface is on board.
• PACHC — the electrohydraulic control module: the card that turns the PAC120 into a hydraulic axis controller. Each PACHC-460-01 controls 1–2 hydraulic axes in position, force or pressure, including change-over between position and force control, with a 250 µs controller cycle. It has 4 analogue inputs (0–10 V, optionally 0/4–20 mA, 12 bit) for pressure and force sensors, 4 analogue outputs (±10 V, optionally 0/4–20 mA, 16 bit) for the valves, and digital position feedback for SSI, EnDat 2.1 and incremental encoders (RS422, 5/24 V).
• PACIO — the remote I/O system for the rest of the machine: digital and analogue inputs and outputs, temperature (Pt/Ni) and counter modules, bus couplers and extenders. The modules share the same EtherCAT E-bus, so local and distributed I/O look the same to the program.

Modules are simply lined up next to the controller on the rail. One PAC120 drives up to 20 hydraulic axes — two per PACHC module. Through a PACIO extender module the PAC120 can also control other EtherCAT devices, for example a Parker drive-controlled pump or EtherCAT valves, so pump and axes run from one controller.

Software that shortens commissioning

Programming happens in one environment for logic, I/O, visualisation and motion. Parker supplies a library of motion functions and free application templates — synchronisation of 2 axes, synchronisation of 4 axes, change-over position/force control and a table of records — so typical press and positioning tasks do not have to be written from scratch. All device parameters are stored fail-safe in flash. For machines controlled by a Siemens PLC, Parker publishes a GSDML device description and function blocks for TIA Portal, so the PAC120 fits into an existing S7 architecture as a PROFINET device. The PAC120 can just as well run as a stand-alone machine controller.

What the axis controller brings to the machine

• shorter cycle times thanks to fast, precise position control instead of limit switches and slow approach speeds
• higher process accuracy and repeatability — position, force and pressure under closed-loop control
• less scrap, because force and position are reproduced exactly in every cycle
• lower power consumption and simple connection to other systems via PROFINET, EtherNet/IP, EtherCAT, Modbus TCP and OPC UA

Typical applications

• hydraulic presses — position-controlled pressing and force-controlled holding with change-over
• die-casting and injection-moulding machines
• machine tools, clamping and feed axes
• synchronised cylinders — 2 or 4 hydraulic axes moving in sync
• hydraulic power units with accumulators, where the pump should run only when oil is needed

Which product for which task

Prices, documentation and help with the choice

All products mentioned here are in our shop with list prices, technical data and the complete Parker documentation — catalogues, operation manuals, declarations of conformity, EPLAN macros and, where Parker publishes them, 3D data — on the product's Documentation tab. Not sure which combination fits your machine? Contact us with a short description of the task and we will help you choose the drive, controller and modules.

Products in this article

• Parker AC30V frequency inverters — pump drives with the hydraulic control application
• Parker PAC120 automation controllers — hydraulic (PAC120-P…) and motion (PAC120-M…) versions
• Parker PACHC electrohydraulic control module — 1–2 hydraulic axes per module
• Parker PACIO remote I/O system — bus couplers, extenders, digital, analogue, temperature and counter modules
• Parker PAC340 motion controllers — for larger machines with electric and hydraulic axes