Subscription based control system to automate management of events for robots

IDL - International Digital Library Of
Technology & Research
Volume 1, Issue 5, Mar 2017 Available at: www.dbpublications.org
International e-Journal For Technology And Research-2017
IDL - International Digital Library 1 | P a g e Copyright@IDL-2017
Subscription based control system to automate
management of events for robots
Shruthi S
dept. of Computer Science and Engineering
CMRIT
Bangalore, India
e-mail : deepikaelectric@gmail.com
Abstract—
In Industrial Robots, a human machine interfaces (HMI) provide
means to command and control robots for various purposes.
Generally, this is implemented in a reactive manner by using
polling (or pull) methodology to manage the events. This
methodology restricts the possibilities of automation for reacting
to events thus requires a human operator to poll and react to the
events based on the skill of the human operator. This sometimes
causes non-optimal or wrong responses. This paper proposes a
design methodology to dynamically tap the events using a
subscription based control system for event based management
of robots. This design enables the client to be light-weight, cost
effective and makes the responses more reliable. The paper also
scrutinizes the alternative design options using semantic web for
multirobot coordinative activities.
Keywords- Human Machine Interface (HMI); polling;
subscription
I. INTRODUCTION
Robots play a pivotal role in improving the quality of the
work in a shorter time period by optimizing the costs and
quality yielding success. An industrial robot is a mechanical
system with a robot manipulator and a controller. It is an
intelligent agent that perceive inputs from the percepts and
send back the response actions through actuators. The behavior
of the robot agent is specified through agent function, which
maps the percepts to the response actions. Designing an
interface to a live robot agent is a complex engineering process,
hence online programming is used widely in product
development industries to mimic the actual hardware.
II. EXISTING SYSTEM
The communication between client and server is witnessed
based on a specified analytic model, programmed in the
software. The server being Robot controller(Real/Virtual)
and client essentially is any device which connects to server
through the set of APIs
forming a full fledged Web Service. These services can be
operated via various clients.
Multiple bots can be manipulated by a single controller.
The prevailing operating framework use polling methodology
to receive the events. Requirements for such HMI systems
vary considerably depending on the application. Various
different types of clients (REST, HMI devices, touchscreen
control systems, laptops, desktop PCs, etc.,) provide user-
friendly interfaces and generally very familiar to users.
The Model View Controller architecture isolates the
Business logic, HMI display and context based control from
each other to synchronously interact with each other.
1. View Component including the Icons, menu structure
and the key handlers.
2. Model component include analytic/domain knowledge
for each context selected through keypress which corresponds
its specific command.

3. Robot Controller(Real/Virtual)- Server Module which
responds to the command requested by Client HMI.
Pitfall associated with polling method is, dynamic response
cannot be expected for any event at server.
Communication API : The reliable communication is
ensured by, HTTP, the Application layer protocol which is
placed over TCP/IP layered architecture.
Server : Hosted on a particular port configured and listens
to the client requests. The server module internally implements
message passing and parsing in the stub which receives the
client requests and de-serialize the message, un- marshall it and
dispatch the message to the appropriate control module.
Clients : Real /Virtual manipulator stubs, which conceal
the code for compiling and linking(locating the server,
formatting the command, communicating to server module,
wait and receive the response from server).
Command Based Polling
Command Based Long Polling
Current design of the system is command based. On
demand basis client has to request (send a command GET) to
the server to retrieve/poll for any response. In long polling
technique, the client wait for a predefined time to hear from the
server. The reflex action for any request is completely
deterministic, based on the case specific analytics defined for
the system.
III. PROPOSED SYSTEM DESIGN
The envisaged system proposes a subscription based system
developed using websocket which provide client effective, less
expensive and hastlyfree access. The new design is similar to
existing functionalities, but capable of controlling the robot
with light weight design. The concepts which are already
existing in the system is effectively utilized/reused to suit the
requirements of the current work.
Subscription Sequence
Communication API: HTTP based on architectural style
REST providing reliable communication
Client : Send the request through client stub with
websocket connection.
Server : Send the response through server stub over
websocket connection.
Server Response Representation : Web Services supports
two type of representation: XML and JSON. XML is the
default representation. All resources in Web Services follow
the same pattern. When returning XML, the XML is in
accordance with the XHTML syntax, which uses the XHTML
elements.
Subscriptions : A client should first create a subscription
by specifying the resources of interest via HTTP POST request.
Once the subscription is created, the client can establish a web
socket connection to receive updates on the subscribed

resources.
The above diagram is the Subscription Based System
proposed.
The service on a query will be responded by server over
the architectural style REST. The structured components of the
system makes the system itself well or organized.
The subscription module opens up bidirectional connection
from HMI client to the Controller and break down if either one
is not functioning. Connecting software with hardware can be
solved by using industry standard APIs and SDKs through
which the windows program communicates with industrial
hardware devices. Proprietary tools are used for the virtual
system creation.
IV. IMPLEMENTATION TECHNIQUE
The server listen to clients on a standard port (say port 80
for http requests). Client sends a POST command to server
specifying the resources for which it expects the automatic
response. The RESTful client can send request through the
browser using the application layer HTTP protocol. The
fundamental elements of HTTP protocol are the HTTP verbs -
GET,POST,PUT,DELETE. Thus Controller return response
back through these verbs in XML or JSON format.
For a new HMI client to utilize the websocket module, up-
gradation of socket type is essential. The resources for which
subscription is an asynchronous request from client where
progress of the event is continuously monitored by an explicit
GET request from client. Thus, for the above set up HTTP
protocol maintains session information through the cookies.
The cookies preserve the <name, value> pair over multiple
Http requests. The proposed implementation stores the
sessionId information in the cookie (instead of the entire
information) and through that ID, retrieves the information
from server. A spike solution can be found at [5].
A sample REST client can be downloaded from [6] and
used as the reference for debugging. A full-fledged python
client can be downloaded from [7] by following the steps
mentioned. It is to be noted that websocket module can work
with python version above 3 (3.4 and 3.5 used for current
testing).
The server side socket should include and support the
websocket module which can be downloaded from [8] (The
server compatible to the client version). The installation steps
can be referred from [9] using pip. Essentially the controller
component contains the server websocket enabler modules.
The client implementation vary depending on the
requirement and technology used for development.
One solution is to use Directly the client libraries like
POCO C++ Libraries that can be sourced and used from
opensource for C++ development [10]. It is a foundation
library which builds an abstraction layer containing huge utility
classes and stream classes. These libraries can either be built
from the command line or visual studio .net. Advantage of
using the library is that it is easy to develop and time to market
value is high if used in product development. The pitfall is that
it makes the design more complex and its heavy in terms of
memory if a small feature has to be used for any light weight
client.
Another alternative is to use a light weight library at client
side supporting the websocket like "libwebsockets C library"
sourced from [11]. Advantage is the light weight library can be
used for light weight client development with a minimal
development time.
Once the client and server spike solutions are ready,
implement the best possible alternative by enhancing the
existing model to websocket based framework.
V. FUTURE EXTENSION
The subscription model can be appended with the semantic
web concept which can be used for coordinated and
collaborated actions of robot.
The knowledge learning systems like RoboDB gathers
response actions from various robots. And the same knowledge
base can be integrated with the current framework at the server
end (central server for numerous clients) [1].
In a multi robot operating environment [4], the task is
distributed among various robots and by executing the task
executed by each robot, the entire action can be executed as a
whole. The co-ordination among the robots can be established
by event based actions controlled at server end. When robot 1
completes its assigned task invokes a command and the robot
which would have subscribed for the robot 1' s completion, will
kick start automatically when the corresponding event/flag is
signaled. Similarly, after robot 2 completes, signals the
successive collaborative actions which are controlled using the
Semantic Web Service Ontologies. These Semantic web
service combines processes from one or more robots thus
automating multiple programs/processes to work in a
collaborative fashion.

VI. CONCLUSION
The project finds its importance if it gets implemented for
the industrial robots which are currently getting operated with
polling functionality. The proposed module would provide
organizational success by being light weight HMI for
controlling the robot. The design considerations make the
system extensible and reuse the existing code and making the
design cost effective.
ACKNOWLEDGMENT
I am highly indebted to my Mentor and Project guide,
Principal and Professor, Computer Science and Engineering of
CMRIT, Mr. Sanjay Chitnis , Ph.D. (IISc) for their constant
guidance and supervision as well as for providing necessary
information regarding the work undertaken.
REFERENCES
[1] Alex Juarez, Jun Hu, and Loe Feijs “RoboDB: an application of
Semantic Web Technologies to robotics
[2] David Obdrzalek on Usage of real-world robotics in Semantic Web.
[3] Zhengjie Fan1, Elisa Tosello2, Michele Palmia3, and Enrico Pagello2 on
, “Applying Semantic Web Technologies to Multi-Robot Coordination”
[4] Yuichiro Mori, Yuhei Ogawa, Akatsuki Hikawa, and Takahira
Yamaguchi on , “Multi-robot Coordination Based on Ontologies and
Semantic Web Service”
[5] https://docs.python.org/2/library/cookie.html
[6] https://github.com/wiztools/rest-client
[7] https://pypi.python.org/pypi/websocket-client
[8] https://pypi.python.org/pypi/websocket-server/0.4
[9] https://wiki.python.org/moin/CheeseShopTutorial
[10] https://pocoproject.org/
[11] https://libwebsockets.org/lws-api-doc-master

Subscription based control system to automate management of events for robots

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à Subscription based control system to automate management of events for robots

Similaire à Subscription based control system to automate management of events for robots (20)

Dernier

Dernier (20)

Subscription based control system to automate management of events for robots