Control System Forming A Logic Display

Abstract

A sequence control system having switching and output modules arranged on a mounting member to form a ladder network which displays and implements the control logic appearing on a ladder drawing of the control system. The mounting member utilizes a ladder-shaped structure having contact and output modules mounted on the structure legs and powered through the struts connecting these legs. Each contact module is an AND gate having displayed on its face the normal state of the contacts it represents and the controlling element of that module. Each output module is a driver element having displayed on its face the element it controls. The modules are arranged according to a ladder drawing which drawing is displayed by the sum total of the module faces when the control system is assembled.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to control systems in general and more particularly to small, sequence control systems having a limited input and output range which systems do not warrant the complexity of a programmable memory.

2. Description of the Prior Art

A sequence control system is generally designed and depicted, by those familiar with the art, in the form of a ladder drawings. This is the standard representation of a machine control and is the symbolic representation of the relays, output devices, and contacts used to implement the logic of the control system.

In detail, the vertical lines of the ladder drawing represent power input lines. Contacts appear along the horizontal lines of this drawing and indicate logical AND functions. All these contacts must be closed to allow power to be applied to an output device which is represented by a circle on the extreme right of the horizontal line. These contacts may be any combination of both normally open and normally closed contacts. Normally open contacts are indicated by open lines. Normally closed contacts are indicated by a diagonal slash appearing across the normally open contact symbol described previously.

Logical OR functions are indicated by a connecting line between horizontal lines of the ladder drawing. This shows a parallel connected flow of logic to the output device. Contacts along either parallel branch when all closed, up to the junction point, will AND with the modules appearing after the junction point, which when closed, will activate the output device.

Traditionally relays have been used to implement the sequence control indicated by the ladder drawing. Relays are available in a variety of configurations, however, all are characterized by a coil and a movable armature which opens and closes output contacts. Each relay is energized by a logical combination of inputs which allow power to be applied to the coil under the right conditions to activate the output contacts. The output contacts of the relay are used in the control system to activate certain variables causing an orderly sequence of control operations.

Although the relay system is wired from a ladder drawing, there is no correlation between the physical arrangement of relays and contacts and their symbolic layout on a ladder drawing. This is due to all the contacts of a relay and the coil being a part of the same physical device. Thus troubleshooting and replacement of a faulty relay is difficult and time consuming since cross-reference drawings are needed to locate the relays associated with the faulty logic. Also, despite the fact that relays are reliable, they are subject to sticking contacts and mechanical failures. Further, relay life is of short duration and does not warrant their reuse when a control system is redesigned.

In recent times, solid state and fluidic logic components have been developed which are used in control systems. These components offer increased reliability and life since they are not subject to sticking contacts and other mechanical frailties exhibited by relays. However the control systems utilizing these components are nevertheless in a format that is not readily identifiable with its corresponding ladder drawing. In fact the physical arrangement of these components in most control systems correlates less closely with the ladder drawing than even a relay system.

Programmable controllers are available which provide a visual interpretation of the flow of logic of the control system on their programming panels. However these controllers solve Boolean equations by the execution of instructions stored in their memory banks. The system control by these devices occurs by programming the controller memory within the format appropriate to the controller rather than directly from a ladder drawing. Thus the logic display is in the appropriate language used and not as a ladder drawing.

The present invention contemplates new and improved apparatus, the utilization of which apparatus overcomes all the above referred to problems and others and provides a control system which is easily operated and which corresponds directly to the control system ladder drawing.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a sequence control system in the form of a ladder shaped network of either fluidic or electric contact and output modules. This control system performs combinational logic functions on various system input and output signals to allow an orderly succession of functions as required by the control system.

The arrangement of the control system is such that a ladder drawing of the contact states which allow the various system outputs to be energized is displayed by the ladder network of the control system. This is accomplished by having each ladder network contact module act like as well as display the corresponding contact notation of the ladder drawing for that control system. Each network output module acts like and displays the corresponding relay coil or output device notation of the ladder drawing for that control system. Further the actual output state of each module is displayed by an "on" "off" condition indicator connected to the output of each module. Thus when the module is providing an output signal, the indicator is "on," and when there is no module output the indicator is "off."

The control system contact modules are logic AND gates having counterparts familiar to both persons skilled in the electric as well as fluidic arts. Thus the control system can be either electric or fluidic. The output modules could be any power driving means familiar to those skilled in the electric and fluidic arts such as DC to AC converters or standard electric amplifiers for the electric control system and booster relays or pressure to electric converters for the fluidic control system. Similarly those familiar with the art could choose any well-known indicating means as a light emitting diode to be used as the indicator for the electrical system, while for a fluidic control system a two color, pressure activated flag could be used. Regardless of the system being electric or fluidic, each contact module will include one input, one control signal, one output and a contact display on its front face corresponding to the ladder drawing contact for which it is acting. Similarly each output module will include one input, one output and a display on its face of the system control element it controls.

The arrangement of this sequence control system causes a display of a ladder drawing of the control system while at the same time functioning identically to the ladder drawing. A view of the control system displays a labeled ladder drawing of the control system. This is a tremendous aid in not only wiring but troubleshooting the system.

Further in accordance with the invention there is provided a contact module suitable for use in the above described sequence control system. This module provides an input and a control signal connection and produces an output only upon a logical combination of the input and control signal. Furthermore it has a legend on its face which identifies its normal state and the control element. This makes it an ideal control system building block since it not only functions as a contact element of the ladder drawing of the control system but also displays the part of the ladder drawing it corresponds to.

Further in accordance with the invention there is provided an output module suitable for use in the above described sequence control system. This module converts an input signal to an output signal capable of controlling an output element. Furthermore it has a legend on its face indicating the output element it controls as well as its input. This allows the output module not only to function as the output element of the ladder drawing of the sequence control system but also displays the ladder drawing element it corresponds to.

Since these modules are logic AND gates and long life amplifiers, the sequence control system may be dismantled and the parts reused as well as making the system programmable merely by rearranging the contact and output modules according to a new ladder drawing of the new control system.

Further in accordance with the invention there is provided a module mounting frame in the form of a ladder to which the previously described contact and output modules may be mounted. The struts provide mounting for the modules as well as supplying the power to the modules. The main structures supporting the struts provide rigidity to the control system as well as providing the system power which is distributed to the struts of the mounting frame. This mounting frame allows the modules to be assembled onto it in a manner that displays a ladder drawing of the control system when the frame is viewed. The control system may be reprogrammed merely by rearranging the contact and output modules in conformity to the ladder drawing of the control system desired.

Thus the principal object of the invention is to provide a sequence control system arranged and acting in the manner of the ladder drawing of the system.

Another object of the invention is to provide a sequence control system which also indicates the individual output state of its components by an indicator means to facilitate troubleshooting and circuit tracing.

Another object of the invention is to provide a modular sequence control system which is easily programmed and reprogrammed or altered at an individual ladder drawing contact level by replacement and reorganization of modules on the ladder network.

Another object of the invention is to provide modules which can be easily arranged in a ladder network to act like and display a ladder drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a generally accepted method of depiction of a control system in the form of a ladder drawing.

FIG. 2 depicts a sequence control system ladder network corresponding to the ladder drawing of FIG. 1.

FIG. 3 depicts a normally open contact module utilizing an AND gate.

FIG. 4 depicts a normally closed contact module utilizing an AND gate and an inverter.

FIG. 5 depicts an output module utilizing a driver.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purpose of illustrating the preferred embodiment of the invention only and not for the purpose of limiting same, FIG. 1 shows a ladder drawing 10 of a sequence control system which activates circled output devices or relays 1CR and 2CR by a combination of the contacts 3LS, 5CR, 9CR, 3CR and 2PS, 4CR respectively.

More particularly the relay 1CR is activated by the logical combination of contact 3LS and contact 5CR AND contact 9CR OR contact 3CR AND contact 9CR. Similarly relay 2CR is activated by the logical combination of contact 2PS AND contact 4CR. It will be understood that the number of branches as well as the number and combination of contacts depends entirely on the requirements of the control system.

Referring now to FIG. 2, a sequence control system ladder network 20, which can be either electric or fluidic, has network fluidic power input lines 22, within the vertical bars 33, between which are connected module mounting bars 26a, 26b, 26c in a manner that allows the power to be distributed to the bars 26. Normally-open contact modules 28, normally-closed contact modules 30, and output modules 32 are operably mounted on the mounting bars 26 at power output points 21 which power the modules. The mounting is in a one-to-one position and function correspondence to the contacts and output devices or relays in the ladder drawing set forth in FIG. 1. The modules 28, 30, 32 all have module output indicators 31 which indicate the presence and absence of an output signal from the corresponding modules. The indicators 31 can be neon bulbs or light emitting diodes in electric networks, and two color pressure activated flag indicators for fluidic networks, or other similar devices which are known by those familiar with the respective arts. The front of each normally open and normally closed contact modules 28, 30, have symbols 34, 36, respectively indicating the type of contact function employed by the modules (normally open, normally closed). These drawings are in standard notation known to those familiar with the art of control systems. The output modules 32 have circles 38 on their front face, within which are indicated alphanumerically the machine function controlled by the respective output module. Each contact module also has an alphanumeric representation on its face of the contact on the ladder drawing 10 it corresponds to. This alphanumeric representation also indicates the pilot device from which that particular contact module derives its control signal. It is thus seen that by viewing the ladder network 20 along with the front faces of the modules 28, 30, 32 a ladder drawing as set forth in FIG. 1 is displayed by the network 20.

In operation, the various contact modules receive control signals from their respective pilot devices 19 by way of lines 25. These pilot devices take the form of limit switches, level switches and relay contacts as well as other devices familiar to those skilled in the art. Contact modules also receive input signals from other modules and push button or selector switches from control operators. The normally-open contact modules require a true signal both from their input lines as well as their control lines to activate their outputs. The contact modules are powered by supply connections (not shown) from the ladder network 20 as is well known to those skilled in the art. Thus in module mounting bar 26a, module 3LS will produce an output when the control signal from its manual start input and its associated pilot device are both true. This output will then serve as the input signal for module 5CR which will also produce an output when the control signal from its associated pilot device is true. The output of module 5CR then acts as the input for normally closed contact module 9CR. This module acts in a manner different from modules 3LS and 5CR in that it produces an output only if there is a false signal from the pilot device associated with it and a true signal from the previous module. Should this condition exist, then module 9CR provides an output which serves as an input signal for the output module 1CR. The output module produces an output signal level in response to the input signal, which is capable of controlling a machine function by way of elements (not shown) familiar to those skilled in the art such as solenoids, relays, coils, motor starters and others. The output signal is transmitted by control output lines 43 connected to the output modules 32. Thus we see that modules 3LS, 5CR, and 9CR all function in AND logic to produce an output signal.

A logic OR function is provided by wiring the output of 3CR normally open contact module in bar 26b to the input of contact module 9CR in bar 26a by a connecting wire 27. This allows the output from the 1CR output module to be also activated by the 3CR and 9CR contact modules ANDed together.

Contact modules 2PS and 4CR in bar 26c are ANDed together to provide an input to output module 2CR, the output of which controls another machine function.

For an electrical system the vertical bars 33 can distribute the two sides of an appropriate voltage supply (not shown). The modules can then be electrically wired together and grounded to the bars 26 by means familiar to those in the electrical control art. For a fluidic system the vertical bars 33 function as the air supply lines which feed the contact modules through power output points 21 in the bars 26 through manifolds which are well known to those in the fluidic arts.

Referring now to FIG. 3, the normally-open contact modules 28 comprise an AND gate 40, which can be electrical or fluidic. The gate 40 input signal is applied to an input 42 by way of module connecting lines 41, external switches, or from the mounting bar 26. The control signal is applied to a control signal input 44 by way of the proper signal from lines 25 originating from the pilot devices 19 or other contact modules. When both the input 42 and the control 44 provide a true signal to the AND gate 40, the output is activated and transmitted through the output line 46 to the module connecting lines 41. This output also activates the module contained indicator 31 which is directly connected in the output line 46 and is activated only by the output of its corresponding module.

Referring now to FIG. 4, the AND gate 40 in conjunction with a signal inverter 48, which changes a true signal to false and vice versa, comprises the normally closed contact module 30. The connection and operation is similar to the module 28 described in reference to FIG. 3 with the exception of the control signal being inverted. In this module, the control signal from line 25 is connected to the inverter 48 which provides a signal opposite to the one supplied by the pilot device 19 to the AND gate input 44. Thus the gate 40 output is activated when a true signal exists at input 42 and a false signal exists at control signal line 25.

Referring now to FIG. 5, the output module 32 includes a driver 50. The function of the driver 50 is to convert the input signal received at a driver input 52 from the module connecting line 41 thus providing an output through driver output line 54 which is able to activate a machine control through output lines 43. For a fluidic system, the driver 50 can be a booster relay, pressure/electric transmitter, or any other fluidic signal modifying device. For an electrical system, the driver 50 can be a DC to AC converter, electric/pneumatic transmitter, a DC amplifier, or any other similar electrical signal modifying device.

Obvious modifications will occur to those familiar with the art. As an example a timer may be connected into the control system to delay the relaying of an output signal to the next associated device. This timer may be incorporated as a separate module within the ladder network 20 or as a device external to the ladder network 20. Similarly a memory device to hold the input signal within the ladder network 20 until reset occurs could be incorporated externally or appear as a separate module within the ladder network. It is intended that this description not be limited to the embodiment described, but to be inclusive of the mentioned examples as well as all other similarly obvious modifications.

Claims

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A sequence control system comprising:

a ladder shaped structure having means for conducting power along the struts of said structure;

a plurality of contact modules operationally mounted to the struts of said structure for executing logic functions in response to input signals to said control system;

an output module operationally mounted to a strut of said structure for providing an output signal from said control system in response to the executed logic of said contact modules; and

said contact modules and said output module having appropriate markings to display and function in the manner of a ladder drawing of said sequence control system.

2. A sequence control system as set forth in claim 1 including means, individually mounted to said contact and output modules, for indicating the output condition of each of said contact and output modules.

3. A sequence control system as set forth in claim 2 wherein said indicating means is directly connected to the output of said output module to provide indication whenever an output signal appears from said output module.

4. A sequence control system as set forth in claim 3 wherein said contact modules are logic AND gates.

5. A sequence control system as set forth in claim 4 wherein a supply power source is distributed to the struts of said structure for parallel connecting said contact modules on each strut of said structure.

6. A contact module for providing and displaying switching functions in a sequence control system comprising;

a module body;

an input signal connection located at a side of said module body;

an output signal connection located at a side of said module body;

a control signal connection located at a side of said module body; and,

a legend located on a face of said module body indicating input and output connection lines connected to a contact, the normal state of said contact, and the element which provides said control signal.

7. A contact module as set forth in claim 6 wherein said output signal connection is powered in response to a logical AND combination of signals to said input signal connection and said control signal connection.

8. An output module for providing an output from a sequence control system to control an output element comprising:

a module body;

an input connection located at a side of said module body;

an output connection located at a side of said module body; and

a legend located on the face of said module body indicating input connection line connected to an alphanumeric representation of said output element controlled.

9. A module mounting frame, in the form of a ladder, for use in a sequence control system comprising;

a set of substantially parallel main structures to which a driving potential is supplied to power said frame;

a plurality of substantially parallel module mounting members oriented between and substantially perpendicular to said main structures; and,

said mounting members providing paths for conducting the potential applied to said main structures when modules are mounted on said mounting members.