The programmable robots or PLC




Until not long ago time the industrial process control venia becoming of form twisted by means of cocking mechanisms and relays. To the worker who was in charge of this type of facilities, it was demanded to him to have  stops technical knowledge to be able to make them and later to maintain them.  In addition any variation in the process supposed to physically modify great part of the connections of the assemblies, being necessary for it a great technical effort and a greater economic payment.

    At the present time a complex process cannot be understood of high level  developed by twisted techniques. The programmable computer and robots have taken part of considerable form so that this type of facilities has been replaced by controlled others of programmed form.

    The Industrial Programmable Robot (API) was born like solution to the control of complex circuits of automatization. Therefore it is possible to be said that a API is not more than an electronic device that replaces the auxiliary circuits or of control of the automatic systems. To him the receivers (final of race, pulsers, etc...), and the actuators (coils of cocking mechanisms, lamps, sin receiving you, etc...) by another one connect themselves on the one hand.

Fields of application

A programmable robot usually is used in industrial processes that have one or several of the following necessities:

General applications:

And as so digimos previously, this talks about the industrial programmable robots, leaving of side the small robots for more personal use (than they are possible to be used, even, to automate processes in the home, like the door of a garage or the lights of the house).

Advantages and disadvantages of the PLC's

Between the advantages we have:

And between the disadvantages:

To day of today the disadvantages have become null, since all the races of engineering include the automatization like one of their subjets. As far as the cost there is no problem either, since there are robots for all the necessities and to fit prices.

 

The PLC's was introduced for the first time in the industry in 1960 approximately. The main reason of such fact fué the necessity to eliminate the great cost that took place when replacing the complex system of control based on relays and cocking mechanisms. Bedford Associates proposed something denominated Modular Digital Controller (MODICON, To modulate CONtroler Digitalis) to a great manufacturer of cars. Other companies simultaneously proposed schemes based on computer, one of which was based on the PDP-8. MODICON 084 turned out to be the first PLC of the world in being produced commercially.

The problem of the relays was that when the production requirements also changed it made the system of control. This began to be quite expensive when the changes were frequent. Since the relays are mechanical devices and have a limited life required a strict planned manutención. On the other hand, sometimes connections between hundreds or thousands of relays were due to make, which implied an enormous effort of design and maintenance.

The "new controllers" had easily to be programmable by engineers of plant or maintenance personnel. The time of life had to be long and the changes in the program had to be made of simple form. Finally one prevailed that they worked without problems in adverse industrial surroundings. The solution fué the use of a technique of familiar programming and to replace the mechanical relays by solid state relays.

In the middle of the 70 dominant technologies of the PLC they were sequential machines of state and CPU based on displacement of bit. AMD 2901 and 2903 were very popular in the Modicon and PLC's A-B. The conventional microprocessors yielded the power necessary to solve of fast form and completes the small logic of the PLC's. By each model of microprocessor there was a model of PLC based on the same one. However, the 2903 fué of the most used.

The communication abilities began to appear approximately in 1973. The first system fué the bus Modicon (Modbus). The PLC could now engage in a dialog with other PLC's and altogether they could be isolated of the machines that they controlled. Also they could send and receive variable signals of tension, entering the analogical world. Unfortunately, the lack of a standard accompanied with a continuous technological change has caused that the communication of PLC's is an incompatible maremagnum of físcicos systems and protocols between if. Despite fué a great one decada for the PLC's.

In the 80 an attempt of standardization of the communications with protocol MAP (Manufacturing Automation Protocol) of General Motor's took place. Also fué a time in that the dimensions of the PLC were reduced and went to program with symbolic programming through personal computers instead of the classic terminals of programming. Nowadays the smallest PLC is as large as a simple relay.

The 90 have shown a gradual reduction in the number of new protocols, and in the modernization of the physical layers of the protocols more popular than they survived the 80. The last standard (IEC 1131-3) tries to unify the system of programming of all the PLC in an only international standard. Now we have PLC's that can be programmed in block diagrams, list of instructions and text structured at the same time.

The PC is beginning to replace to the PLC in some applications, even the company that introduced Modicon 084 has changed to the control based on PC. Thus, it would not be to be strange that in a future not very distant the PLC in front of disappears more and more the powerful PC, due to the possibilities that the computers can provide.

 

    Let us see a typical circuit of automatism. A Estrella/Triángulo starter with timer.
    Figure 1 shows  as it is the twisted technique. On the one hand we have the circuit of force, that  feed the motor, and by another one the auxiliary circuit or of control,  that make the maneuver of starting of this motor.

    Figure 2 shows as the same assembly of programmed form is made. The circuit of force is exactly the same one that in the twisted technique. Nevertheless, the one of control will be replaced by a programmable  robot, to who the pulsers and the coils of the cocking mechanisms are united electrically. The starting maneuver made the program that previously has transferred the robot.

 


 

PARTS OF A PROGRAMMABLE ROBOT

The basic structure of any robot is the following one:

With respect to their external disposition, the robots can contain several of these sections in a same module or each one of separated them by different modules. Thus Compact and Modular robots can be distinguished.

Power supply
     She is the one in charge to turn the tension of the network,  220v c.a.,  to low tension of c.c, normally 24 v. Being this the tension of work in the electronic circuits that the Robot forms.

CPU
     The CPU is the authentic brain of the system. One is in charge to receive you order them, of the worker by means of the programming console and I modulate of entrances. Later it processes them to send answers to the module of exits. In its memory is resident the program destined  to control the process.

I modulate of entrances
     To this module the receivers are united electrically (interrupting, final of race, pulsers...).
     The information received in him, is sent to the CPU to be processed in agreement the resident programming.

 

Passive receivers

 

 

Active Receivers

. 
    Two types can be differentiated from conectables receivers  to the module of entrances: the Liabilities and the Assets.
    The Passive Receivers are those that change their logical state, activated - not activated, by means of a mechanical action. These are the Switches, pulsers, end of race, etc.
    The Active Receivers are electronicses that need to be fed by a tension so that they vary his logical state. This it is the case of the different types from detectors (Inductive, Capacitivos, Photoelectric). Many of these apparatuses can be fed by the own power supply on the robot.
    The one that knows circuits of industrial automatism made by cocking mechanisms, will know that it can use, like receivers, contacts electrically opened or electrically closed depending on its function in the circuit. As example we can see  a simple starter paro/marcha (fig 5). In him one distinguishes the contact used like on march pulser that normally is set out and the used one like shutdown pulser that normally is closed.
    Nevertheless in circuits automated by robots, the receivers generally are opened.
    The same starter paro/marcha made with a robot is the one of figure 6.  In him one sees that both pulsers and the thermal relay to help are opened.
 

 


 

I modulate of exits
    I modulate of exits of the robot is the one in charge to activate and to deactivate the actuators (coils of cocking mechanisms, lamps, motors sin you, etc).
    The information sent by the entrances to the CPU, once processed, is sent to the module of exits so that these are activated and simultaneously the actuators that in them are connected.
    According to the type of process to control by the robot, we can use different modules from exits.
    Three exist affluent type differentiated:
  - To relays.
  - To triac.
  - To transistors.

Modules from exits to relays.
    They are used in circuits of DC and alternates. They are based on the mechanical commutation, by the coil of the relay, of an electrical contact normally opened.
.


.
Modules from exits to Triacs
    DC and alternating current are used in circuits of that need very fast maneuvers of commutation.

 

 

 

Modules from exits to Transistors to open collector.
     The use of the east type of modules is exclusive of the circuits of c.c.
 Also that in those of Triacs, is used in circuits that need very fast maneuvers of conexión/desconexión.

 

 

    The form to connect the actuators to the modules of exits, will depend on the type of used module. These are some examples:

.

 

 

 

 

 

PROGRAMMING TERMINAL
     The terminal or console of programming is the one that allows to communicate to the worker with the system.
     The basic functions of this one are the following ones:
  - Transference and modification of programs.
  - Verification  of the programming.
  - Information of the operation of the processes.
    As programming consoles can be used the constructed ones specifically for the robot, calculating type or a personal computer, PC, that has specially supported a software designed to solve the problems of programming and control.

 


Terminal of programming
portable

Terminal of compatible programming PC

PERIPHERAL
    The peripheral ones do not take part directly in the operation of the robot, but nevertheless they facilitate  the work of the worker.
    The most used they are:
  - Recorders to cassettes.
  - Printing.
  - Cartridges of memory EEPROM.
  - Visualizers and panels of operation OP
 
 


Panel of Operation

Connection of a visualizer to a robot

 

 

PROGRAMMING LANGUAGES

    When the programmable robots arose, they did it with the necessity to replace the enormous pictures of maneuver constructed with cocking mechanisms and relays. Therefore, the communication man-maquina would have to be similar to the used one until that moment. The used language, would have to be interpreted, with facility, by such technicians electricians who previously were in contact with the enemy  with the installation. These languages have evolved lately, of such form that some of them no longer have nothing to do with the typical electrical plane relays.
    The most significant languages are:

Language to contacts. (LD)
    He is the one that more similarities it has with used by an electrician when elaborating the pictures of automatism. Many robots include special modules of software to be able to program graphically of this form.

 


.
Language by List of Instructions. (IL)
    In the robots of low range, it is the only way of programming. It consists of elaborating a list of instructions or nemónicos that are associated to the symbols and their combination in an electrical circuit to contacts. Also to say, that this type of language is, in some the cases, the fastest of programming and even most powerful form.
 

 

GRAFCET. (SFC)
    It is the Graphical call of Order Stage Transition.  Specially it has been designed to solve problems of sequential automatism. The actions are associated to the stages and the conditions to fulfill to the transitions. This language is enormously simple to interpret by workers without knowledge of electrical automatism.
    Many of the robots who exist in the market allow the programming in GRAFCET, as much in graphics mode or as by list of instructions.
    Also we can use it to solve problems of automatization of theoretical form and later to turn it to plane of contacts.

 

PLANE OF FUNCTIONS. (FBD)
    The plane of functions logics, turns out specially comfortable to use, accustomed technicians to work with circuits of doors logics, since the simbología used in both is equivalent.

 

 

 

ROBOT TSX17-10

    To the being the this inferior model of all range TSX, makes us have economic a programmable robot, of great ideal power and in addition to use it with didactic aims.
   Before happening to describe the used programming language, it is necessary to know his electrical structure and its characteristics external.
   

CHARACTERISTICS

    The TSX17 is a mini-robot of compact type. The CPU, power supply, section of exits, and section of entrances, is including in the same module.
    The programming console is external.

 
    The connection of cartridges EEPROM is made directly in the lodging reserved for it in the own robot.
    All the connections become through two strips of easily replaceable tips in case of mechanical or electrical deterioration.
    The feeding can be included/understood between 110-240 v.
    Usable v in c.c. has an exit of 24 to connect passive receivers as as much active.
    The 8 exits to relays (everything or nothing) are free of tension.
    The 12 digital entrances are activated by the 24 volts of c.c. that gives the power supply of the own robot.  Also they are digital.
    The maintenance of octetos ram memory, 8k, becomes by a battery with duration of an a or.
    Pins is possible to expand the possibilities of the robot by means of the connector of 9 located in the frontal of the apparatus.
    The subjection to the electrical closet can easily be made by track DIN.
    The frontal panel of leds, that allows to verify the state of Entrances and Exits, is easily replaceable.
 

STRUCTURE OF THE TSX17-10

    As he indicated himself in the previous point, the robot  is of compact structure. Power supply, section of E/S and CPU are including in the same module. Its outer aspect corresponds to the one of the figure:

 

    The connection of captadores/actuadores to the entradas/salidas ones of the robot is made of the following form:

 

 

 EXPANSION POSSIBILITIES

  The TSX17-10 even being the youngest child of all the family of robots of Telemecanique, allows  their association to other modules of E/S, digitalises (everything or nothing) and analogical. The only condition that is to fulfill is that a number of 2 extensions is not surpassed.
    The initial module will be the M0, the first M1 extension and the second M2 extension (fig xx).  We will very tend this in account at the moment for elaborating the programs.

 

 

 

TERMINAL OF PROGRAMMING TSX T317

   Although the objective of this document is not to present the use the console of programming, it is going away to graphically represent his physical form and the access the different menus that this one allows us.

 

 


Accesses to the different ways from programming and control with the T317 terminal

   The following scheme shows to the different functions supported by the console from programming and the form to accede to them:

 


Union TSX17 <-----> PC

Our robot can take advantage of the power the personal computers for his programming.
    Union TSX17/PC is made with an Interface that turns protocols RS232 to RS485. This Interface distributes to Telemecanique  with reference TSX 17 ACC8 to it, being necessary in addition kit to connections TSX 17 ACC11.
    As software is used a programming module, by list of instructions, specially designed by Telemecanique.

 

 
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