Digital and Analog Interfaces

Fast Commands and Easy Integration

Control Using Digital Interfaces

Fast USB or TCP/IP interfaces as well as RS-232 are the standard interfaces supported by modern digital controllers from PI.

Beyond that, PI also offers real-time compatible interfaces such as an SPI or a 32 bit parallel In- / Out-interface (PIO).

To establish the connection to the application environment, customer-specific serial interfaces are also possible.

Analog Interfaces: Commands in Real-Time

In the case of analog drivers, the analog input value is amplified linearly and the output voltage is transmitted to the drive. Analog motion controllers, as still used for piezo-based positioning systems, are equipped with an analog proportional, integral, and differential (PID) controller and linearization processes through which the input voltage corresponds as close as possible to the target position. The resolution and process time thus depend directly on the components used and allow subnanometer motion and real-time command.

Many of the PI digital motion controllers are also equipped with analog interfaces which can be used for external sensors or as a source for generating a position value. To achieve the real-time ability and resolution of an analog controller, PI employs fast processors and high-resolution 16 to 20 bit A/D converters with oversampling processes.

Analog outputs can be used as monitor of the axial position or to control an external motor drive.

In addition, PI offers an analog interface for many controls as connection to external operating elements such as joysticks. Modern PI controllers support HDI equipment for this purpose which are linked to the controller using a USB interface.

EtherCAT: Synchronous Clock for the Entire Automation Line

Hexapod systems are offered for integration into automation trains with optional field bus interfaces. Currently, exchangeable modules such as Profibus, EtherCAT, Profinet, CANopen and SERCOS are available. The hexapods are of modular design and come with a host of different drive solutions. They can therefore be customized within short periods of time.

Due to a direct connection to the master control, hexapod systems can be integrated into virtually any automation system and cycle synchronization with other automation components is easy to implement, e.g., for automated feeds etc. This opens a number of application fields for hexapod systems in automation technology, starting with metal cutting through to complex bending processes.

In such applications, the programmable logic controller (PLC) can communicate with the hexapod system over a standardized field bus interface. The PLC acts as master and defines the target position in Cartesian coordinates and the trajectories; in return, it also receives the actual positions over the field bus interface. All other calculations required to command the parallel-kinematic six-axis system are done by the hexapod controller, i.e., transforming the target positions from Cartesian coordinates into drive commands for the individual drives.

In this case, the controller acts just like an intelligent drive. The cycle times for determining new positions, evaluating signals and synchronizing are between 1 and 3 ms.

Customized Direct Commands: Serial Peripheral Interface (SPI)

Serial data transfer using the SPI is mainly intended for transmitting digitalized position values from the PI controller and control signals to the PI controller. Transmission is with marginal delay and update rates which correspond to the servo cycle times of the controller.

Here, the standard command interpreter for the PI General Command Set (GCS) can be bypassed, thus making conversion of the commands obsolete. This is of special interest for users if own digital signals are to be integrated real time for target values.

Alternatively, GCS commands can also be transmitted, so giving access to all the functions of the controller. In addition to linking external controls, the PI SPIs are also used for internal data transmission between the controller and mechanical elements.

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