Overview

The prbt_hardware_support package contains files supporting the certification of a robot system including the PRBT manipulator according to DIN EN ISO 10218-1. As safety controllers the Pilz hardware PNOZmulti and PSS4000 are supported. A Modbus connection is used for the communication between ROS <-> safety controller.

There is no need to call these launch files directly; they are included from prbt_support/robot.launch.

STO

The STO function (“Safe torque off”) of the robot arm is a safety function to immediately turn off torque of the drives.

SBC

The SBC function ("Safe brake control") of the robot arm is a safety function which is used in conjunction with the STO and prevents a motion when the torque of the drives is turned off.

Safe stop 1 (SS1)

To allow a controlled stop, the safety controller delays the STO signal by several milliseconds. This package opens a modbus connection to the safety controller (PNOZmulti or PSS4000). The safety controller sends an emergency stop signal via Modbus immediately so that ros_control has a short time interval to stop the drives via a brake ramp. The TCP could for example brake on the current trajectory. After execution of the brake ramp, the drivers are halted. Even if ROS would fail, the safety controller turns off the motors via STO (that would be a Stop 0 then).

Possible error cases and their handling

Error cases Handling
Modbus client crashes ROS system is shutdown which leads to an abrupt stop of the robot.
STO Modbus adapter crashes ROS system is shutdown which leads to an abrupt stop of the robot.
Connection loss between PNOZmulti/PSS4000 & Modbus client Stop 1 is triggered
System overload (messages don't arrive in time) In case a Stop 1 message does not arrive in time, the safety controller will automatically perform a hard stop. In case a Stop 1-release message does not get through, brakes will remain closed.
STO Modbus adapter cannot connect to stop services ROS system will not start.
STO Modbus adapter cannot connect to recover services Node does start and robot can be moved until a stop is triggered. Afterwards the brakes will remain closed.

Brake tests

Brake tests are an integral part of the SBC, since they detect misfunctions of the brakes or the brake control in general. Brake tests for each drive have to be executed at a regular interval. When the safety controller requests brake tests, they have to be executed within 1 hour, else the robot cannot be moved anymore.

Operation Modes

The robot system can be controlled in various modes.

These modes are:

See DIN EN ISO 10218-1 for more details or contact us: ros@p.nosp@m.ilz..nosp@m.de

Note

In operation mode T1 the robot can be moved as usual. However, if an attempt to exceed the speed limit of 250 mm/s in T1 is detected, the prevailing motion is aborted and a controlled stop is performed.

Architecture

The following diagram shows all components of the system and the connections between them.

diag_comp_overall_architecture.png
Component diagram of overall architecture

ROS API

ModbusClient

A Modbus client (for usage with the PNOZmulti or PSS4000) can be started with roslaunch prbt_hardware_support modbus_client.launch.

Published Topics

Parameters

Please note:

ModbusAdapterStoNode

The ModbusAdapterSto is noticed via the topic /pilz_modbus_client_node/modbus_read if the STO is true or false and reacts as follows calling the corresponding services of the controllers and drivers:

ModbusAdapterBrakeTestNode

The ModbusAdapterBrakeTestNode offers the /prbt/brake_test_required service which informs if the PSS4000 requests a brake test or if a brake test request is no longer prevailing.

BraketestExecutorNode

The BraketestExecutorNode offers the /execute_braketest service which, in interaction with the CanOpenBraketestAdapter, executes a braketest on each drive of the manipulator. This can only be done, if the robot is stopped. So, if you want to execute a braketest, ensure that the robot stands still.

ModbusAdapterOperationModeNode

The ModbusAdapterOperationModeNode publishes the active operation mode on the topic /prbt/operation_mode everytime it changes and offers the /get_operation_mode service for accessing the active operation mode.

Use rosmsg show prbt_hardware_support/OperationModes to see the definition of each value.

OperationModeSetupExecutorNode

The OperationModeSetupExecutorNode sets the speed limit for each frame based on the active operation mode and offers a service /prbt/get_speed_override. The speed override is chosen such that a speed limit violation is unlikely if all robot motions are scaled with it.

Parameters

SpeedObserverNode

The SpeedObserverNode observes the speed of the robot frames and triggers a controlled stop, if the current speed limit is exceeded.

Parameters

*Not supported yet



prbt_hardware_support
Author(s):
autogenerated on Sat Oct 19 2019 03:15:47