A Variant of a Low-Channel Telemechanical Crane Control System

A. L. Linenko, I. S. Avramov, A. I. Zaitsev, S. S. Kronin

(Presented by the scientific seminar of the Electromechanical Faculty)

The proposed system provides for combined manual and semiautomatic control of crane mechanisms with the use of an electronic computing device.

The system may be used on industrial technological cranes of any purpose and may serve as the basis for the comprehensive automation of enterprises. The system makes it possible automatically to bring the travel mechanisms to any specified coordinate (bridge, trolley), and also provides for remote manual control of all mechanisms (bridge, trolley, hoist, etc.) from a control desk located outside the crane. The standard control circuits for the motors of the crane mechanisms remain unchanged (P, PS, T, TS, etc.).

For control, a low-channel group-distribution number-pulse telemechanical system is used. For the automatic positioning of mechanisms at a specified point, the following discrete-action systems are employed, including computing devices.

The principal elements of the system are the control desk, encoder, communication channel, decoder, computing devices, correction systems, and a block of actuating relays.

Control Desk

The control desk includes command apparatus for manual and semiautomatic control and a mnemonic diagram of the exact stopping points.

Encoder (Fig. 1)

For transmitting control commands, a number-pulse code has been adopted, which best ensures reliable transmission and reception of commands. Each command is encoded by a four-digit number. The position of the first digit determines the type of control, and the digit itself determines the nature of the control (manual, semiautomatic control, and emergency commands). For manual control, the position of the second digit indicates affiliation with a mechanism, and the digit itself gives its name (bridge, trolley, hoist, etc.); the position of the third digit indicates the direction of motion, and the digits themselves mean “stop,” “forward,” “back”; the position of the fourth digit indicates the speed of motion, and the digits themselves indicate its magnitude.

For semiautomatic control, the second digit determines the coordinate of the precise stop for the trolley, and the third and fourth determine the coordinate of the precise stopping point of the bridge.

The initial carrier of the commands is the clock pulses (CP), generated by the clock-pulse generator (CPG). The CPG is a multivibrator, frequency-stabilized at a frequency chosen on the basis of the required command-transmission speed.

Fig. 1.

The clock pulses are fed to the CP distributor (CPD). The CPD consists of a binary counter connected to a diode network that has gaps for forming pauses between groups of CPs.

The CPD ensures sequential transmission of commands: first the semiautomatic-control command passes, then, in succession, the commands for manual control of the trolley, hoist, and bridge. Subsequently the cycle is repeated as the CPD counter overflows.

The RTI is connected to the command apparatuses (CA), which are multicontact switches. As many buses approach each CA as there are qualitative attributes in the command.

A qualitative attribute carries information distinguishing one command from another. For example, a manual-control command contains the attributes: type of control (manual), association with a mechanism (bridge), direction of motion (“forward”), and speed of motion (“first”).

Transmission of a command is carried out in a definite sequence corresponding to the logic of execution. Therefore the qualitative attributes must be formed and executed in the order of their importance.

The clock pulse, passing through the CA, is routed along the last bus at a definite output, thereby acquiring the required qualitative attribute.

All output buses of the CA are combined into groups according to the principle of commonality of the numerical code and are connected to logical separation circuits “OR,” each having one output. The output buses of the “OR” circuits are connected to the input buses of the setting circuit. The setting circuit is made in the form of a diode network forming a fixed storage device (FSD). The fixed memory stores the binary code and distributes the input TI over the output buses of the setting circuit in complementary code. The command recorded in complementary code enters the command-pulse counter and is stored as a combination of flip-flop states. The outputs of the flip-flops are connected to the “AND” circuit, which fixes the zero state of all flip-flops (fixation of “0”).

The “AND” circuit (fixation of “0”) is connected, through an amplifying device, to the command-pulse generator (CPG), which is a multivibrator. The CPG frequency is selected from the condition of ensuring the required pause between groups of command pulses. The CPG output is connected to the command transmitter and to the input of the command-pulse counter. The CPG is in a stable state (pulses are not generated) when zero is fixed, i.e., all counter flip-flops are in state 0. When a binary number is entered into the counter, zero fixation is absent and the CPG is started. The command-pulse generator produces a number of pulses that complements the received number (in complementary code) to the number corresponding to the capacity of the counter. In this case, the number of command pulses produced by the CPG corresponds to the direct code. Having received the last pulse, which complements the number recorded in the counter to the number corresponding to the capacity of the counter, the counter overflows and all flip-flops are set to the zero state. At this point the zero-fixation circuit disconnects the command-pulse generator. Thus, each clock pulse is converted into a group of command pulses, with the number of pulses in each group corresponding to a specific qualitative attribute of the command. The command transmitter (CT) is made as a voltage amplifier and serves to amplify the command pulses transmitted into the communication channel. The gain factor of the CT is selected by calculation so that the amplitude of the command pulses significantly exceeds the noise level.

The emergency “Stop” command is issued when the “Stop” button located on the control panel is pressed. This disconnects the GTI from the TI distributor, terminates transmission of any commands, and consequently frees the communication channel for the emergency-stop command. At the same time, in the unit forming the “Stop” command, one pulse is formed and transmitted into the communication channel.

denoting this command. For reliability in transmitting the emergency command “Stop,” it is formed and sent in addition to the encoder.

The forming device for the “Stop” command consists of a differentiating \(RC\) circuit connected to the voltage source through the “Stop” button, and a one-shot multivibrator triggered by an \(RC\) circuit. The one-shot multivibrator creates the time delay necessary for preparing the decoder to receive the “Stop” command.

Communication Channel

A two-core shielded flexible cable, wound onto a tension drum, is used as the communication channel. The cable is tensioned by a torque motor.

Decoder (Fig. 2)

The command pulses (CP) from the communication channel enter the receiver, where they are filtered and shaped.

Fig. 2.

Because the overall command is transmitted in parts, the decoder must evaluate not only each part separately, but also

and the entire command as a whole, transmit it to its destination, and prepare for receiving a new command. The first group of pulses arriving at the decoder, carrying information on the mode of control, enters the control-mode commutator and is stored. Depending on the number of pulses in the first group, the corresponding channel of semiautomatic or manual control is opened, and the channel of the control-mode commutator is also closed. Now the second group of pulses will pass through this commutator, without affecting it, to the corresponding channel to the following commutators.

Simultaneously with the arrival of the first pulse of the first group, the extinction-forming device is switched on; after the entire command has been received, it sets the whole decoder circuit to its initial state, preparing it to receive the next command. When the emergency command “Stop” is sent, transmission of all other commands ceases; the decoder goes into its initial state and receives the arriving “Stop” command in the control-mode commutator, forwarding it directly to the block of executive relays.

The second group of pulses, for example for semiautomatic control, enters the coordinate commutator of the mechanisms, which, after receiving the entire second group of pulses, switches the semiautomatic-control channels of the trolley or bridge in accordance with the received information and sends this group of pulses to the corresponding buffer storage devices of the trolley or bridge. The number of pulses in the group (i.e., the number of the precise stopping point of the given mechanism) is stored for some time in the buffer storage device, which is a counter. The state of the trigger cells corresponding to the number of pulses is transferred, by means of a readout device, into the state of the trigger cells of the storage device for the coordinates of the precise stopping points, which belongs to the executive device.

After the information from the buffer storage device has been transferred to the storage device for the coordinates of the precise stopping points, which has long-term memory, the information in the buffer storage device of the precise stopping points is erased. Preparation then takes place for receiving the next information.

The information accumulated in the decoder storage devices is erased by the extinction-forming device after the command-transmission cycle has ended.

When the second group of pulses of a manual-control command arrives, it passes along the manual-control channel through the “open” key \(K_1\) (key \(K_2\) is closed) into the manual-control mechanism commutator and is stored there. After a certain time, necessary for completion of the transient process, the mechanism commutator opens key \(K_2\) and closes \(K_1\). Thus, the following, third group of pulses will pass through the open keys \(K_2\) and \(K_3\) into the direction-of-motion commutator; the information of this group will be stored, and after the time required for reliable reception of this command, the commutator will close key \(K_3\) and open key \(K_4\). The last, fourth group of pulses freely passes into the speed-of-motion commutator, without affecting the first commutators. The information of this group is likewise stored.

Thus, at the outputs of all manual-control commutators, the command that was transmitted by the corresponding groups of pulses is established.

As an example, let us consider one of the circuits (Fig. 3). The commutator circuit contains three main elements: keys, switching elements, and a storage device. The keys are several “AND” coincidence circuits. In the initial state—

...the key connecting the commutator with the information channel (“\(I_1\)”) is open; the keys connecting the information channel with other devices are closed (“\(I_2\)”). The group of command pulses passes through key “\(I_1\)” and is received by the storage device of the commutator, consisting of trigger cells combined into a binary counter connected with a diode matrix—decoder. The number of trigger cells is determined by the number of pulses in the command group and, by virtue of the selected coding method, which is distinguished by a small number of pulses in the group, is small. As a rule, the storage device consists of two trigger cells. The buses of the diode matrix—decoder ensure transmission of information to the required devices; in addition, when necessary, the connection of the buses of the diode matrix with the keys causes the latter to be switched depending on the information received. A waiting multivibrator is also connected to the output of key “\(I_1\),” started by the very first pulse of the arriving group of pulses. The waiting multivibrator, with a time delay, controls the switching trigger cell, which in turn is connected with the keys. The delay of the waiting multivibrator, on the one hand, must be greater than the reception time of the command pulse group and, on the other hand, less than the clock interval, so that before the arrival of a new pulse group the necessary switchings have been completed.

The trigger cells of the commutator storage device and the switching trigger cell have a common quenching circuit, connected with the entire quenching circuit of the decoder, for returning the latter to its initial state after reception of a command.

Structural diagram

information channel

commutator

information transmission

typical block diagram of the commutator

key

\(I_2\)

diode matrix—decoder

from the quenching commutator

to the switching trigger

quenching

information channel

\(I_1\)

\(M_v\)

to the information switching trigger

Fig. 3.

The commutator for the mode of control is analogous to the described commutator circuit. Its storage device controls the operation of key 5, which opens the manual-control channel or the semiautomatic-control channel (s.a.).

The commutator of the mechanisms for semiautomatic control consists only of switching elements. The storage devices of the coordinates of the TTO, of the bridge and trolley mechanisms, are separated out (in view of their importance), together with the readout devices, as separate elements of the decoder circuit.

The commutators of the mechanisms of manual control and of the direction of motion are analogous to the commutator described.

The movement-speed switch is intended for receiving the pulses of the fourth group of the command; therefore it contains no switching devices.

The blanking-formation device consists of a monostable multivibrator and the forming device proper. Transmission of the command is performed in a maximum of 4 cycles. The delay of the blanking monostable multivibrator has been taken, from the conditions of reliable operation of the decoder, as equal to 4.5 times the cycle time.

The blanking monostable multivibrator is started by the first pulse of the first group of pulses of each command and, after the delay time, applies a pulse to the amplifying device, which generates a powerful blanking pulse causing the erasure of information in all memory units of the decoder and the switching of all keys to the initial state.

A special feature of the channel for semiautomatic control is the presence of buffer memory units with a readout device. The buffer memory units serve for short-term storage of the information received by the decoder. The readout device serves to read out the information stored in the buffer memory units into the long-term memory units of the coordinate TTO of the computing devices. The readout device is a group of “AND” coincidence circuits. One of the inputs of each “AND” circuit is connected to the output of a trigger cell of the buffer memory unit. All second inputs of the “AND” circuits of each buffer memory unit are connected to a common bus, to which the readout signal is also applied. The outputs of the “AND” circuits are connected respectively to the set inputs of the corresponding trigger cells of the long-term memory unit. When the readout signal is applied, the “AND” circuits pass this signal in accordance with the state of the trigger cells of the buffer memory unit. The trigger cells of the long-term memory unit, unlike the trigger cells of the buffer memory unit, are not connected into a binary counter; they are switched, bit by bit, into the same state in which the trigger cells of the buffer memory unit were at the moment of readout. Thus the information of the TTO coordinate of the corresponding mechanism, written in the form of a binary number in the trigger cells, is read out.

Obviously, readout must be carried out after the information has been received by the buffer memory unit, but before the signal for erasing the information is applied. The readout signal, both for the buffer memory unit of the TTO coordinates of the trolley mechanism and for the buffer memory unit of the TTO coordinates of the bridge mechanism, is supplied by the chain: readout monostable multivibrator—emitter follower. The delay of the readout monostable multivibrator, started by the first pulse of the third group of pulses of the semiautomatic-control command, is chosen from the condition of ensuring that the readout signal is applied after the group of command pulses has passed into the buffer memory unit of the bridge mechanism.

A special feature of the manual-control channel of the decoder is the presence of an additional decoding device. This device serves to transmit the information received by the memory units of the switches of the manual-control mechanisms, directions of motion, and speed of motion to the corresponding block of executive relays of the corresponding mechanism.

The decoding device consists of “AND” coincidence circuits forming three groups for the three manual-control mechanisms. The output buses of each group of “AND” circuits are connected to the relay block of the corresponding mechanism. Each first input of the “AND” circuits is connected to the common bus leading to the switch of the manual-control mechanisms. The second inputs of the “AND” circuits are connected groupwise to common buses leading to the switches of direction of motion and speed.

motion. Thus, the control signal is sent to the relay blocks in pulse form. The duration of the control pulse is determined by the storage time of the information in the storage device of the decoders’ switchboards.

Computing device (Fig. 4)

Upon receipt of a semiautomatic-control command, the process of controlling the motion of the bridge and trolley travel mechanisms is carried out by the computing device.

Fig. 4.

The computing device is a tracking system of discrete action, controlling the crane motion as a function of distance. Obviously, in this case the distance must likewise be measured in discrete quantities, called unit segments. The scale of the unit segment is chosen from the conditions of the required stopping accuracy of the mechanism.

The distance traveled is counted by a unit-pulse sensor (Fig. 6), which, after a distance equal to one unit segment has been traversed, sends a pulse to the storage device of the coordinates of the current position.

The unit-pulse sensor is a block consisting of a light source, a photoresistor, and an amplifier on semiconductor triodes. The photoresistor is illuminated through an opening in a disk kinematically connected with the mechanism drive. When the mechanism traverses one unit segment of distance, the photoresistor is illuminated once.

The principal element of the storage device for the current position of the mechanism is a reversible binary counter, the number of trigger cells of which is determined by the selected number of unit segments. The process of storing the coordinates of the current position of the mechanism reduces to counting unit pulses while taking into account the direction of motion, which is indicated by the direction-of-motion sensor.

The direction-of-motion sensor (Fig. 6) is kinematically linked with the mechanism and, in the simplest case, is a tachogenerator. The polarity of its voltage determines the direction of motion and is used to control a sign flip-flop cell, which switches the reversible counter of the memory device for the current position either to addition or to subtraction of units.

Upon receiving the coordinates of the point of precise stopping to which the crane must automatically move, the computing device must determine the direction of motion (forward or backward), the magnitude of the travel speed (high or low), the braking instant for transition from high speed to low speed, the braking time instant for stopping the crane, and, finally, the “Stop” command when the crane reaches the precise stopping point.

All these commands are generated as the result of comparing the coordinate of the precise stopping point with the current position of the corresponding mechanism.

The coordinates of the precise stopping point are stored in the storage device for the coordinates of precise stopping points.

Comparison of the current coordinate with the specified one (or, what is the same thing, of the distance traveled with the specified distance) for determining the direction of motion takes place in the device for determining the direction of motion. If, for example, the specified distance proves greater than the distance traveled, the command “Forward” is generated; if it turns out that the distance traveled has become greater than the specified distance, the command “Backward” is generated.

For generating the remaining commands, a comparison device is used, in which the remaining distance is compared with distance settings corresponding to the transition from high speed to low speed, as well as to the beginning of braking and to final stopping. These settings are quite definite and are memorized by the comparison device.

The result of comparing the remaining distance during movement of the mechanism with the distance settings is fed to the device that forms the control signals. The signal obtained as a result of the comparison goes to the block of executive relays.

The coordinates of the current position of the mechanism and of the precise stopping points (PSP) are expressed by a binary number with the aid of flip-flop cells. Each cell corresponds to its own binary digit. In order to save elements and simplify the circuit, it is desirable that the PSP coordinates be expressed by several binary digits, called the higher-order digits. The remaining digits we shall call the lower-order digits. Thus, precise stopping points must be spaced from one another by an integral number of digits (higher-order ones).

Comparison of coordinates is reduced to comparison of the numbers stored in the corresponding memory devices; it is carried out digit by digit. In the process of comparison it is necessary to determine whether the given two digits coincide or, if they do not coincide, to determine which of the digits is greater.

The binary-digit coincidence circuit consists of two “AND” elements. The inputs of one “AND” element are connected to the “zero” outputs of the flip-flop cells of one digit of both memory devices. The inputs of the second “AND” element are connected analogously to the “one” outputs. The outputs of the “AND” circuits are connected by an “OR” circuit, at whose output a signal appears only when the digits coincide.

Let us consider the formation of the “Stop” command.

Since the “Stop” command is issued when there is complete coincidence in both the higher-order and lower-order digits, to generate it it is sufficient to combine in a coincidence circuit the outputs of the digit-by-digit coincidence circuits—

in the higher-order digits and the output of the zero-fixation circuit in the lower-order digits. To fix a “zero” in the lower-order digits, it is sufficient to combine the “zero” outputs of all the trigger cells of the lower-order digits in a coincidence circuit.

Formation of the Direction-of-Motion Command

To determine the direction of motion, it is necessary to compare two numbers and determine which of them is larger. These numbers are represented in binary code by the corresponding binary digits. Obviously, there is no need to compare the numbers completely, in all digits; it is enough to compare the highest-order digits representing these numbers. In the general case, the comparison must begin with the highest-order digits of the storage devices, and if they coincide, proceed to the next digits.

The circuit for determining the direction of motion “Forward” for the highest-order digit consists of an “AND” element, whose inputs are connected to the “zero” output of the trigger cell of the current-position memory and to the “one” output of the trigger cell of the exact stopping point coordinates. For lower-order digits, the outputs of the coincidence circuits of the higher-order digits are fed into the “AND” element.

Since the coordinate of the exact stopping point is determined only by the higher-order digits, then when moving “Forward,” when the coordinate of the current position of the mechanism is less than the coordinate of the exact stopping point, there will be no coincidence in the higher-order digits until the exact stopping point is reached. Therefore, in this case the circuits for determining the direction of motion of the higher-order digits ensure the correct indication of the direction of motion “Forward.” For this purpose these bit-by-bit circuits are combined into an “AND” circuit having one common output.

Since the command “Backward” is the negation of the command “Forward,” to generate it it is necessary to connect a “NOT” element to the output of the “Forward” command.

Formation of the Commands “Low Speed,” “Braking,” and “High Speed”

The commands “Low Speed” and “Braking” are issued when the mechanism reaches the specified path settings. Since the capacity of the lower-order digits determines the distance between exact stopping points, and the settings for transition to “Low Speed” and “Braking” are considerably smaller than the distance between exact stopping points, the commands “Low Speed” and “Braking” must be generated only by the lower-order digits of the current-position memory. The issuance of the command “Low Speed” at path setting M and of the command “Braking” at path setting T must be carried out:

1) when moving “Backward,” under the condition of complete coincidence in the higher-order digits and with the numbers set in the lower-order digits: for “Low Speed” the number \(A \leq M\), for “Braking” the number \(B \leq T\);

2) when moving “Forward,” under the condition of coincidence in the higher-order digits except the last one, and with the numbers set in the lower-order digits: for “Low Speed”—\((C - A)\); for “Braking”—\((C - B)\), where \(C\) is the capacity of the lower-order digits.

Figure 5 shows a block diagram for generating the “Braking” command for a setting of 5 unit intervals for motion “Backward.”

With the lower-order digits are connected four groups of coincidence circuits “AND.” The outputs of each group are connected into an “OR” circuit. The first group fixes the numbers \(A\), the second—\((C-A)\), the third—\(B\), and the fourth—\((C-B)\). The outputs of the “OR” elements of the first and third groups are connected with a coincidence circuit in all higher-order digits by an “AND” element.

Fig. 5.

“AND.” Thus, the signal for transition to “Low speed” and “Braking” is supplied when the specified path settings are reached during “Backward” motion.

The outputs of the “OR” elements of the second and fourth groups are connected with the coincidence circuit of the higher-order digits (without the last one) by an “AND” element, thereby ensuring formation of the signal for transition to “Low speed” and “Braking” when the specified path settings are reached during “Forward” motion.

The circuits for generating the commands “Low speed” and “Braking” during both “Forward” and “Backward” motion are combined by “OR” circuits to obtain the general command “Braking” or “Low speed.”

To generate the command “High speed,” a “NOT” element is connected to the output of the command “Low speed.” Thus, the command “High speed” is the negation of the command “Low speed.”

Correction System

During the motion of crane mechanisms, owing to slipping of the driving wheels and skidding, the distance traveled as counted by the unit-pulse sensor may be determined with an error. In order to eliminate a possible error in determining the current coordinates of the mechanism, a correction system is provided. The correction system is connected with a travel-correction sensor. This system changes, in the storage device for the current position of the mechanism, the value of the current position so as to eliminate the error that has arisen in determining the actual position of the given mechanism.

The correction must be introduced rapidly, as the mechanism passes the correction-entry points.

Correction pulses are generated by the travel-correction sensor, which provides an accurate count of the distance traveled. (The bridge travel-correction sensor counts the distance relative to fixed points on the shop wall. The trolley travel-correction sensor counts the distance relative to fixed points on the bridge structure.)

The correction pulses from the sensor enter the storage device for the correction-entry points. The signal indicating the direction of motion is also fed there.

In the comparison device, the information on the actual position of the mechanism is compared with the position recorded in the storage device of the current position of the mechanism. If an error is present, the sign of the correction is also determined there. The signal carrying information on the sign of the correction is transmitted to the “Correction sign” element, which performs switching in the “sign cell” in such a way that the motion-direction channel is disconnected and the correction-sign signal enters the storage device of the current position of the mechanism. At the same time, the comparison device sends a signal to the correction-generating device, which connects the correction-pulse generator to the storage device of the current position of the mechanism for a certain time. Thus, correction pulses are entered into the storage device of the current position of the mechanism; this continues until the numbers in the storage devices of the correction-entry points and of the current position of the mechanism coincide, or until the end of the entry time determined by the time delay of the waiting multivibrator. The time delay determines the connection time of the correction system.

By introducing the correction, the information stored in the storage device of the current position of the mechanism is quickly changed to that which characterizes the exact position of the corresponding mechanism.

Relay Block (Fig. 6)

The relay block of the entire circuit consists of the blocks of actuating relays for the bridge-travel and trolley-travel mechanisms and of the relay block for the hoisting mechanism.

The indicated relay blocks of all mechanisms are connected to the output buses of the decoder and of the computing device and serve as amplifiers for the control commands entering them. The relay block consists of pulse relay amplifiers which, after a command pulse arrives, switch to self-holding.

The amplified control commands are fed to the control circuits of the hoisting, bridge-travel, and trolley-travel motors (of types PS and P), where they perform the corresponding switching operations.

Main Interlocks

To ensure reliable operation of the circuit, interlocking connections between individual elements are used in it.

The interlocking connection between the command apparatuses of semiautomatic and manual control permits operation in automatic mode only when the command apparatuses for manual control are in the zero position. If the manual-control switch for the bridge or trolley is moved to any position other than zero, the automatic system is disconnected and control is transferred to manual mode.

Fig. 6.

The interlocking connection between the computing device and the safe-height sensor of the hoisting mechanism automatically establishes the safe height of the tongs during trolley travel, ensuring safe motion of the crane-travel mechanisms and maximum productivity. This interlock is effected by the switching device only under semiautomatic control of the travel mechanisms.