Distributed Control Cams with ETHERCAT

Concept

The devices CI511-ETHCAT and CI512-ETHCAT can be used as distributed electrical cams with communication over ETHERCAT.

The encoder, which has to be the first slave of the line structure, generates the reference axis.

Each device has up to 8 (CI511-ETHCAT) respectively 16 (CI512-ETHCAT) digital outputs and up to 32 cams. The cams can be mapped to the digital outputs according to the user specifications.

The devices can also process dynamic cams with compensation time for each cam.

The 32 cams of each device can be assigned to any digital outputs, so several switching actions for each digital output and each turn are possible. Each cam consists of one switch-on and one switch-off-action. If a digital output is not assigned to a cam, it can be used as a standard output and controlled by the PLC.

The PLC can further more set any digital output at any time to overwrite the cam state. It can also clear the enable bit of the cams. In this case, the digital output will follow the value in the process image.

This conception allows a flexible utilization of the available digital outputs as cam output or standard digital outputs.

The mapping between the cams and the digital outputs is a part of the configuration and can not be changed online.

Cam Accuracy

The cam in the CI51x-ETHCAT uses the positions with time stamp, which comes from the encoder with each telegram, to calculate its switching time. It uses the internal synchronized clock to eliminate

• dead times,
• jitter of ETHERCAT telegrams,
• cycle time of the encoder.

The accuracy of the CI51x-ETHCAT cams implementation depends only on the number of the projected cams (parameter NumOfUsedCam) of each device.

Cam accuracy (worst case)

Particular Features

In order to reduce the data amount of the process data image, some parameters for the cams, e. g. FirstOnPosition, LastOnPosition and Compensation, are transferred to the ETHERCAT slave using the multiplexing method. Parameters of only one cam out of 32 cams are embedded in each ETHERCAT telegram. The multiplexing mechanism is handled completely by the function blocks. The user program is released from this task.

The enable-bits of the cams are treated differently: They are transferred to the slaves with each ETHERCAT telegram, so the cam can be enabled or disabled very quickly.

Encoder

To facilitate the cam switch functionality, an encoder must be used. The encoder gives the time stamped position of the referent axis to the CI51x-ETHCAT. The encoder must be the first ETHERCAT slave in the line structure.

ABB hardware-components work properly with the 18 bit encoder GBMMS or GBMMW of Baumer-IVO. Different bit resolutions of the encoder can be used, but a high resolution will reduce jitter of the cams. The specified data in Cam Accuracy is applied for encoder with 18 bits resolution.

Further details of the IVO encoder can be found at http://www.ivo.de

Encoder Wiring

ABB Components use ETHERNET cables with RJ45 connectors, but the encoder uses a M12 connector. A suitable connection between the ETHCAT Communication Module (CM5xy-ETHCAT) and encoder respectively between encoder and ETHCAT Communication Interface Modules (CI5xy-ETHCAT) is required. The following connector can be used:

Connection of EM 12 S OCTOPUS:

	Name	ETHERNET cable	EM 12 S OCTOPUS
	TxD+	White/green	Yellow pin 1
	TxD-	Green	Orange pin 3
	RxD+	White/orange	White pin 2
	RxD-	Orange	Blue pin 4

Software Components

In addition to the standard ETHERCAT_AC500 library, there are two function blocks in the MC_EtherCAT_AC500 library: MC_CamSwitch_DC: MC_CamSwitch_DCPS_DigitalPLS: PS_DigitalPLS

The two function blocks allow a simply control of the cams.

Detail information about configuration and programming application with cam can be found in “ETHERCAT configuration examples”.