Vision & Motion: How the automation bus operates in a camera system

Dr. Pahl, Vision & Control GmbH, explains in this interview, why the company uses the Sercos automation bus, how it is integrated into a camera and which requirements the automation bus needs to fulfil.

Sercos International: Why did you choose the Sercos automation bus?

Dr. Pahl: Sercos is an open standard. It gives us wide latitude for implementation at the hardware level. Ethernet-based communication has a lot of advantages when users connect our machine vision equipment to their drive and control systems.

Sercos International: What are the advantages?

Dr. Pahl: It is easy to connect the nodes to a network, system integration is simple and cabling is kept to a minimum. Also Sercos supports highly synchronous operation.

Sercos International: What does highly synchronous operation do for you?

Dr. Pahl: It enables you to simultaneously trigger image capture and store the position of a conveyor belt, etc., so that the position data can be associated with the image processing result. This eliminates the need for additional hardware such as encoders and position sensors.

Sercos International: How is a vision system connected to the Sercos controller?

Dr. Pahl: The vision system is connected as a slave. The Sercos interface on the system supports camera triggering, swapping of the test programs and process data read/write.

Sercos International: How is image capture triggered?

Dr. Pahl: There is an SDDM file which describes the trigger for image capture. Image capture triggering can be synchronous or synchronous with a time offset from the Sercos cycle. Synchronous with time offset is useful when images of a material stream which is in constant motion need to be captured with uniform spacing.

Sercos International: Why is it necessary to swap test programs?

Dr. Pahl: Swapping functionality is an absolute necessity so that the control system can react quickly and seamlessly to part or format changeover.

Sercos International: What is the volume of process data handled by these systems?

Dr. Pahl: I/O process data volume depends on the specific image processing task. The image processing system can for example determine positions, surface areas and colors or check for the presence or completeness of items and much more. Based on the device profile, we are able to define the volume of I/O process data during the configuration phase of the image processing system.

Sercos International: What are some typical Vision & Motion applications?

Dr. Pahl: Wherever there is a need to synchronize multiple axes on a motion system. Examples include robotics, printing, packaging, filling and many assembly and handling operations.

Sercos International: What is the function of the camera, for example, in the Plastic Electronics demo?

Dr. Pahl: Our vision system detects the positional offset of the registration marks relative to each other and sends the deviations over the bus to the printing machine controller. The controller compensates for positional offset using actuators in the print registers.

Sercos International: What are the handling features of the intelligent camera?

Dr. Pahl: vcwin® software is used for configuration and programming. vcwin® is a operating software. Users create and try out the test program which is then transferred from vcwin® to the device where it is stored. From that point on, the vision system runs autonomously. Camera operation and maintenance are performed using the web interface.

Sercos International: What else does Vision have in mind for Sercos?

Dr. Pahl: Our initial goal is bus connectivity for other components such as a lighting controller. These controllers can enable the machine controller and/or an HMI to configure different lighting scenarios. This makes it very easy to quickly alter lighting scenarios following part or format changeover. No Sercos device profile currently exists for machine vision systems. We are working with Sercos International on the definition of a device profile.

Another goal is operation of the vision system more directly from the controller or HMI. At the moment, vision systems have to be pre-configured to operate them, set parameters and run diagnostics. Embedding the vision system programming environment into the controller’s programming environment would greatly simplify things for machine manufacturers and system integrators. However, we are not there yet. We are currently thinking about possible implementation scenarios.

Sercos International: Where else do you see a need for further development?

Dr. Pahl: Direct integration of Vision and Motion depends to a very large extent on our ability to reduce the execution time of test programs and image processing algorithms. Production speeds are constantly increasing. If the results provided by the vision system are to have a direct influence, the algorithms must deliver the results within a short, finite period of time to avoid acting as a bottleneck. Offloading the algorithms to high-speed embedded hardware or programmable logic devices is our way of meeting the ever increasing need for speed.

Sercos International: Thank you very much!