FR2503120A1 - CONTROL DEVICE FOR LOADING AND UNLOADING MECHANISM - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS AN ELEVATION HEIGHT CONTROL DEVICE INCORPORATED IN A FORK LIFT TRUCK. THIS DEVICE IS CHARACTERIZED IN THAT THE CONTROL UNIT 200 INCLUDES AN INTERFACE CIRCUIT 220 TO RECEIVE THE INPUT SIGNAL FROM THE DETECTION UNIT 100 MEASURING THE LIFT HEIGHT OF THE FORK, AS WELL AS A GENERATOR CIRCUIT D 'COMMAND ORDERS 240 INCLUDING A MEMORY 244 FOR STORING DATA RELATING TO A PREDETERMINED ELEVATION HEIGHT AND DATA ENTRY MEANS 246, AND IN THAT THE COMMAND GENERATOR CIRCUIT 240 PRODUCES A COMMAND ORDER TO FROM A COMPARATIVE CALCULATION BETWEEN THE OUTPUT OF DETECTION UNIT 100 AND THE CONCERNED DATA STORED IN MEMORY 244, TO MAKE A CONTROL OF THE DESIRED ELEVATION HEIGHT IN AGREEMENT WITH THE CONTROL ORDER.

Description

The present invention relates to a control device for a mechanism

  loading and unloading and more particularly a height control device

  elevation incorporated into a forklift.

  The present invention is more particularly

  relating to a device for controlling the height of

  which controls this height based on elevation data stored in

a microcomputer.

  As is well known, a forklift with

  fork includes a loading and unloading mechanism-

  as well as a vehicle chassis. The mechanism of

  The loading and unloading system includes an all-round guide rail

  ge vertically, called "amount", and a fork that can slide in this amount. The mechanism further comprises a hydraulic member, for example a hydraulic cylinder, for raising and lowering the fork and for tilting the amount. The prior art relating to the control of loading and unloading, for example to the control of

  the height of elevation, presented a number of

  which can be summarized in what follows.

  Recently, there has been a tendency for elevation height to increase when the loading and

  unloading is carried out by means of a chain

  riot forklift. For example, loading and unloading can be done at a higher height

  at 10 meters. In such a case, it is difficult for an opera-

  to adjust the loading and unloading mechanism

  in such a way that the fork is placed at the height

  determined by looking at the end of the fork, about 10 meters above the operator's seat. Therefore, it is good that the operator can easily perform loading and unloading

  a load in the predetermined position.

  To meet this requirement, the amount is provided, according to the prior art, a limit switch to stop the fork in a predetermined position. When the fork reaches this pre position

  determined, for example at 8,50m above the ground, the

  The control system is designed to light a lamp provided on the operator's control panel or to cut off the drive power for the loading and unloading work. Usually, a load is unloaded on a shelf of a multi-shelf magazine. For this reason, it is necessary to select the radius to determine the desired position. The prediction of a predetermined number of limit switches, for example ten in number, is necessary to be able to serve the entire height of the store. In addition, it may happen that loading and unloading may take place in another store following the change in the place of work. In this case, if the height of the new magazine is different from that of the previous magazine, a

  complicated order is required. In fact, it turned out to be

  possible to perform the loading and unloading

  ment. In addition, from the point of view of the control system according to the prior art, a plurality of circuits

  analog control, constituted for example by a

  boring relay circuits provided respectively with respect to the controlled system such as elevation height control, are incorporated in the control unit of the control device for the loading and unloading mechanism. Before performing the lift operation, an operator makes different adjustments depending on the condition

  elevation height required for the charging operation-

  and unload, and then start the elevation height operation. In this case is constituted an automatic control system which comprises a control system

  opening of a valve provided in a feed circuit.

  hydraulic pressure to actuate a lift cylinder

  tor. Elevation height control is performed to control the valve opening control system based on the difference between the actual lift height and the preset setpoint. However, when the setting is changed to a large extent depending on the variation of the location o is performed

  the loading and unloading operation, it is necessary

  to adjust the automatic control system to stabilize the control system. In other cases, it may happen that the desired security for the command can not be obtained. In addition, such a height control

  of elevation is performed in a series of sequential

  for the loading and unloading operation,

  the control of the elevation height being related to different

  your kinds of orders. Therefore, it is good to

  see supervising the entire control system to get

  a simplicity of the circuits and a harmonious execution

of the order.

  - To take account of the above, another trend

  has been made. The programmed series of commands

  quentials corresponding to the intended operation of loading and unloading is stored in a computer such as a microcomputer. For example, when elevation height control is performed, the partial program

  concerned with the control of the elevation height is called

  from the main program to control the elevation height based on the partial program. In this case, before performing the elevation height operation, an adjustment is made by setting

  memory in the microcomputer the elevation height vi-

  See. When you then press a push button to

  start an automatic lift height operation

  tick, program execution for height control

  elevation begins. Thus, the automatic control system

  which has the opening control system of the aforementioned valve, becomes active on the basis of the order provided by the microcomputer, so that the fork moves

  towards the desired elevation height to automatically stop

  at this height. Therefore, when the amendment

  setting is required, the elevation height is

  is stored in the microcomputer. When calling up programs for elevation height control, simply call the program in question.

  to distinguish it from others.

  In such a device for controlling the height of elevation by computer, it is carried out, before storing the elevation height intended for the fork, the operation of moving the fork towards the target position, and

  this, by a manual operation. This is done

  killed by operating directly, by means of a manual lever, an elevating valve, or by controlling a servomotor

  control of the lift valve, with a pair of

  switches with lowering and lifting levers. In particular

  when the servomotor is controlled by means of

  levers for raising and lowering, an ac-

  misalignment of the lever switches, in the state

  charged, is dangerous. In addition, it is difficult to move

  accurately move the fork to the target position using the lever switches. For this reason,

  more than the actuation of the lever switches, the

  The aforementioned manual lever is required, which results in the device becoming complicated. In addition,

  when a height of elevation is stored in the middle

  computer, if the data relating to the height of the

  are sampled up to the upper limit of fork movement from the lower limit of the fork, there are disadvantages when an automatic lift height control is performed as a result of the condition. loaded or unloaded or the thickness of the fork. The prior art has not disclosed a method for solving such a problem. In addition, when the fork lift speed is

  determined by an automatic control of the height of

  tion from stored elevation height data, and if a shift order is

  given, it is difficult to

  as a result of the fact that the variation characteristic of the opening angle of the lift valve as a function of the speed of raising or lowering of the fork is non-linear and that there is a response time inherent in

  automatic control system. In addition, when the

  When it reaches the target elevation height and then stops at that height, there is no mechanism to slow down the fork movement before stopping. As a result, sometimes the fork is stopped abruptly, which also causes problems to the point of

security view.

  In view of the above, the object of the present invention is to provide a control device for a loading and unloading mechanism allowing

  solve-various types of problems that arise when

  that an automatic control of the height of elevation is carried out from stored data concerning this

elevation height.

  Another object of the invention is to provide an arrangement

  control device for a loading and unloading mechanism which is capable of performing a regular pursuit control of a fork towards a target value at the time of automatic height control

elevation.

  Another object of the invention is to provide an arrangement

  control system for a loading and

  unloading allowing to progressively approach the

  their aim as a result of a response time of an automatic control system, the speed of elevation before or just before reaching the set point is not changed when automatic control of the height of elevation is carried out, which consequently allows to slow down the fork and to stop it safely in the position

referred.

  Another object of the invention is to provide an arrangement

  control device for a loading and unloading mechanism which is provided with low speed stop means provided in an order generating circuit, for example a microcomputer, thereby slowing a fork before stopping in the position aimed, to improve

Security.

  Another aim of the linvehtion is to provide a

  control system for a loading and

  unloading to sample relative data

  at a height of elevation within a predetermined range when elevation height data is

  stored in an order generating circuit, for example

  a microcomputer, which makes it possible to

  a regular automatic control of the height of

vation.

  Another object of the invention is to provide an arrangement

  control device for a loading and unloading mechanism in which the opening angle of a lift valve connected to a lift cylinder, for the purpose of controlling the raising and lowering of a fork, is limited to a predetermined range, thereby stabilizing the rate of elevation when automatic control

  elevation height is achieved.

  According to the invention, this control device for a loading and unloading mechanism adapted from

  to be incorporated into a forklift truck.

  including a detection unit, a communication unit

  in response to the output signal of the detection unit, which control unit calculates on the basis of the output signal of the detection unit and produces a predetermined control signal as a function of the calculated value, and a unit in response to the predetermined control signal, which drive unit outputs a drive output signal so as to vary

  the forklift height of the truck is

  characterized in that the control unit comprises an interface circuit for receiving the input signal from

  the detection unit, as well as a generator circuit for

  control generating circuit comprising a memory for storing data relating to a predetermined elevation height and data inputting means for supplying data to the memory, and in that the control command generating circuit produces an order of control from a calculation of comparison between the output of the detection unit and the relevant data stored in the memory, to achieve a desired elevation height control in agreement

with the order of order.

  The following will be described by way of non-limiting examples

  Various embodiments of the present invention with reference to the accompanying drawing in which: Figure 1 is a block diagram illustrating the construction of a control device for a mechanism

  loading and unloading according to the present invention.

  tion; Figure 2 is an elevational view of a forklift truck to which the present invention is applicable;

  Figure 3 is a front view of the lift truck.

  fork shown in Figure 2; Figure 4 is a view, on a larger scale, of the forklift, illustrated in Figure 3 and in which is incorporated a lift height sensor; FIG. 5 is a block diagram illustrating a first embodiment of the control device for a

  loading and unloading mechanism according to the invention.

  tion; Figure 6 is an elevational view illustrating a

  forklift to which the

  control shown in FIG.

  explain how the upper limits are set

  upper and lower elevation that are stored;

  Figure 7 is a schematic diagram of an algorithm of

  for the control of height data

  of elevation, which are stored in a micro-

  embedded in the control device of the figure; FIG. 8 is a block diagram of a control circuit assuming the function indicated by the algorithm of FIG. 7; Figure 9 is a block diagram illustrating a

  conventional device for controlling elevator height

  for a loading and unloading mechanism; Fig. 10 is a block diagram illustrating a second embodiment of a control device for

  a loading and unloading mechanism according to the

  vention; Fig. 11 is a diagram of an algorithm for performing elevation height control by means of the control device shown in Fig. 10; Fig. 12 is a diagram illustrating the characteristic curve of fork speed variation when elevation height control is achieved by means of the control device shown in the figure;

  Figure 13 is a diagram illustrating the variation

  setting of the valve angle setting signal

  1ien function of the order signal issued from a microordinate

  controller used in the control device illustrated in FIG. 10;

  FIG. 14 is a diagram of an illustrative algorithm

  controlling an automatic speed control immediately before reaching the target elevation height, by means of a third embodiment of the control device for a loading or unloading mechanism according to the invention;

  Figures 15A and 15B show forms of on-

  illustrating respectively the pulse train of the

  tor and the pulse train of the timer, these trains

  of pulses being used in step four of the algorithm

  theme of Figure 14; Figure 15C is a diagram of an algorithm for

  to the production of the timer pulse train repre-

shown in Figure 15B;

  Figure 16 is an algorithm illustrating a

  main program for the automatic control of the height of elevation, this program being used in a fourth embodiment according to the present invention

  Figure 17 is a diagram of an illustrative algorithm

  trant a subroutine for the stop interrupt command

  progressively used in the fourth form of execution

  the invention; FIGS. 1BA and 18B are schematic views explaining an elevation height determination operation performed by means of the control device according to the fourth embodiment of the invention; Figures 19 and 20 are diagrams illustrating the relationship between the lift rate and the valve opening angle in the fifth embodiment of the invention;

  Fig. 21 is a diagram of an illustrative algorithm

  a program for automatically controlling the rate of elevation used in the fifth embodiment of the invention. Fig. 1 is a block diagram illustrating the construction of a control device for a mechanism

  loading and unloading according to the invention.

  This figure shows a detection unit 100 comprising an elevation height sensor 102, a sensor

  tilt angle 104 and a load sensor 106 (cap-

  pressure transmitter). The control device of FIG. 1 further comprises a control unit 200 comprising an interface circuit 220 comprising an elevation height counter 222, a circuit producing control commands 240 which is constituted by a microcomputer

  230 responding to the output of the detection unit 100 furnace

  denies through the interface circuit 120, and a control circuit 260 responding to the control commands issued by the

  240 command order production circuit.

  these 110S and 112S indicate manual adjustment contacts

  which are closed by external orders indicating respectively

  the height of elevation and the horizontal position of

the fork.

  More particularly, the circuit generating the control commands 240 comprises a central processing unit CPU designated by the reference 242, a memory 244 consisting essentially of a random access memory RAM designated by the reference 244A, and a read only memory.

  ROM designated by reference 244B, in which are stored

  data corresponding to predetermined values of elevation height, tilt angle, load or other parameters, and data entry means 246 which are constituted for example by a keyboard to allow an operator to enter desired data. The production circuit of the control commands 240 transmits a control command which is a function of the output signal of the detection unit a00 and the data relating to the elevation height, the tilt angle or the load placed on the fork, data that is stored in

  the memory 244. The control circuit 260 comprises a first

  first elementary control circuit 262 for the elevation height control system and a second elementary control circuit 264 for the elevator control system.

the tilt angle.

  Figure 1 also shows a unit of

  300 train that includes an electric converter /

  hydraulic pressure 320 and a drive unit at

  340. The electrical / hydraulic pressure converter 320 comprises first and second actuators 322, 324 corresponding respectively to the output of the first and second

  second control circuits 262 and 264. The first action-

  neur 322 comprises a drive circuit of a servomotor consisting essentially of switching transistors 322T1 through 322T4 constituting an inverter for controlling a drive motor 322M, and a contact 322S for connecting a DC power supply 322B to the inverter, according to the order provided from the first circuit of

  command 362, as well as a link mechanism

  Means for coupling the output shaft (not shown) of the drive motor 322M to a movable member of a valve

  of elevation, which will be discussed below. In the same way

  the second actuator 324 includes a drive circuit.

  a servomotor consisting essentially of

  sistors switches 324Tl to 324T4 constituting an inverter

  to control a 324M drive motor, and a

  324S to connect a continuous power supply

  naked 3248 to the inverter, depending on the order provided to

  from the second control circuit 264, as well as a mechanism

  connection linkage not shown for coupling the output shaft (not shown) of the drive motor 324M to a

  movable member of a tilting valve which will be

  below. The hydraulic pressure drive unit 340 comprises first and second control valves respectively corresponding to the first and second actuators 322 and 324. The first control valve 342 is connected to

  a lift cylinder 346 for controlling the lift height

  while the second control valve 344 is

  connected to a tilt cylinder 348 to control the angle

  tilting of the amount. A 345P hydraulic pump

  a suitable pressurized oil is connected

  between the first and second control valves 342 and 344.

  Reference 345T indicates an oil tank. The reference

  3455 indicates a contact provided in an electromagnetic valve

  that (not shown), to establish or otherwise

  break, according to an external order, the circulation of the oil from the 345P hydraulic pump. The first

  control circuit 262, the first actuator 322, the first

  first control valve 342 and the lift cylinder 346

  together form a servocontrol circuit for the elevation height control system. In the same way, the second control circuit 264, the second actuator 324 and

  the second control valve 344 and the base cylinder

  348 together constitute a servocontrol circuit

  3ode for the control system of the tilt angle.

  FIG. 2 shows a forklift truck

  to which the control device is applied for a

  loading and unloading mechanism according to the invention.

  tion. The reference 10 indicates a pair of uprights provided on each of the left and right sides of the carriage, each of these pairs comprising an outer mast 10A and an inner mat 10B supported by the outer mat 10A so as to be able to move thereon to up and down. The lower end of the outer mat 10A is mounted on the front face of the chassis 20 of the carriage so as to be able to

  rotate around a transverse axis. The reference 348 indicates

  than the aforementioned tilt cylinder which is mounted on the front portion of the frame 20 of the carriage. A piston rod 348P of the tilt cylinder 348 is connected to the mat

  external 10A of manibre to be able to adjust the angle of rocker-

  the amount 10 forwards and backwards. The reference

  346 indicates the aforesaid lift cylinder which is mounted on the central portion between the two uprights 10,

  the piston rod 346P of this cylinder being connected to the mat

  dull 10B through a sieve wheel support so that the height of the inner mat lOB can be adjusted up and down. Reference 12 indicates

  a spinner wheel rotatably mounted on the upper end

  piston rod 346P and on this wheel passes a chalk 12C. One end of this chain 12C is hooked to the outer mast 11A or the first elevator 346, while the other end of this chain is connected to a movable element 16 which is mounted vertically sliding in the inner mast 10B or even to a fork 18 supported by

the mobile element 16.

  Reference 18F indicates the extreme part or the ex-

  free fork of the fork 18. A load designated by the reference 40 is mounted on a horizontal portion 18H of the fork 18. Also shown in Figure 2 a steering wheel 24 for driving the trolley in the usual manner, a seat 26 for the operator as well as a wheel

before 28F and a rear wheel 28B.

  Therefore, when the lift cylinder 346 is

  fed, the inner mat lOB rises. As a result of this movement

  The fork 18 which is drawn by the chalk 12C rises along the inner mast 10B. This has the consequence that the load 40 which is mounted on the fork 18, is raised. The

  FIG. 3 is a front view of a forklift truck

  as shown in Figure 2 while Figure 4

  represents a part of Figure 3 on a larger scale.

  In this drawing, the same references as in FIG. 2 are used to indicate corresponding elements.

  therefore the detailed description will be omitted. The

  FIG. 4 shows in detail the elevator height sensor.

  102. This elevation height sensor 102 comprises a disk 102S pierced with a plurality of radial slots and which is mounted coaxially with the chalk wheel 12, and a detection unit 102D which may be photoelectric type and which may consist of, for example, a light source and a light detector.

  light (not shown). The split disk 1025 turns

  The number of slots that have passed through is detected by the detection unit 102D. More particularly, this detection unit 102D produces a pulse signal corresponding to the number of slots that have passed through, which makes it possible to detect the height of elevation. As indicated above, the forklift shown in FIGS. 2 to 4 provides an automatic loading and unloading operation.

  by means of the control device of a charging mechanism-

  2 is shown in FIG. 1. FIG. 5 represents a simplified block diagram for purposes of explanation, and in this diagram the same reference numerals as those of FIG.

  Figure 1 are associated with the constituent elements corresponding to

  dent. The address of the memory 244 is designated by the

  tioning a key of the keyboard 246, which allows to store at this address the data relative to the height of elevation. The aforementioned load sensor 106 is usually constituted by a hydraulic pressure sensor for

  detect the pressure of the oil in the lift cylinder 346.

  When the load 40 is not mounted on the fork 18, that is to say in the unloaded state, the hydraulic pressure sensor 106 emits a logic output signal "0" which is applied to the microcomputer 230. On the other hand, when

* load 40 is placed on the fork 18, that is to say at the

  When loaded, the hydraulic pressure in the lift cylinder 346 increases. When the weight of the load 40 exceeds a predetermined value, the hydraulic pressure sensor 106

  delivers a logic output signal "1" applied to the micro-

  230. The output pulse from the elevation height sensor 102 is applied to the microcomputer 230. In this case, the operation is as follows: the output pulses provided by the elevation height sensor 102 are counted by the elevation height counter 222 shown in FIG. 1, although it is not indicated in FIG. 5. A predetermined calculation is performed in the central processing unit 242 from the value thus counted. The calculated elevation height is indicated on a display screen (not shown) provided on

the keyboard 246.

  In the automatic control device of the above elevation height, the microcomputer 230 drives

  the control valve 342 via the motor of

  322M processing so that the value of the control order is equal to the command value previously stored from the information from the elevation height sensor 102, which drives actuation of the actuator

elevator 346.

  It is necessary to move the fork 18 to the predetermined height when the data relating to the

  height of elevation is stored in the memory 244 of the middle

  In this case, if the fork is raised to the maximum height, the hydraulic pressure in the lift cylinder 346 increases even in the unloaded state. As a result, the pressure sensor

  hydraulic 106 is engaged. The microcomputer 230 recognizes

  was then wrongly stated that there is a state of

  ge. For this reason, even if the operator is to be brought to store the data relative to the height of elevation,

  in the uncharged state, in the microcomputer 230, in action

  246, this data is stored automatically.

  address that is allocated to the loaded state. This has

  as a consequence of the inconveniences or errors

  laughter occur when automatically ordering the

  height, whether in the loaded or unloaded state

  gen. Now it will be assumed that the elevation height data is stored in the microcomputer 230

  while the fork 18 is to be lowered to the ground.

  When the thickness of the horizontal part 18H of the furnace

  Che 18 is large compared to the thickness of an oven

  conventionally, even if one tries to lower the fork 18 to a stored position corresponding to the ground, by performing an automatic height of elevation control, it is actually impossible to lower the fork 18 to

  this position. For this reason, the result is a

  deny that the order indicating the lowering of the

  fork 18 is continuously emitted from the microordinate

  230, which makes it impossible to proceed to the subsequent

you.

  The first embodiment of the invention has

  to solve these problems, as will now be explained.

  FIG. 5 shows the upper limit and the lower limit of the height of elevation that are to be stored in the microcomputer 230.

  is indicated by the references XH and XL in FIG.

  In this case, the upper limit to be stored is chosen so that it is slightly less than the height of elevation corresponding to the output of the load sensor 106 associated with the lift cylinder 346, in the unloaded state, while that the lower limit to be stored is chosen to be slightly greater than the maximum value of the thickness of the horizontal portion 18H

  fork 18. The microcomputer 230 executes a program

  based on an algorithm as shown in FIG. 7, where STT signifies departure. In the first step S1, the memory program concerned is examined in

  the main loop to control various types of

  such requirements as the fork lift height control 18 which is stored in the ROM 2448

  of the microcomputer 230. If the memory program is

  During this examination, during the second step S2, the memory program concerned is called. In step 53, the comparison between the stored upper limit of the elevation height value and the actual elevation height data obtained from the elevation height sensor 102 is made in the program. of memory. In step 54, if the result is "minus",

  that is, have the effective value of the elevation height

  is greater than the stored upper limit of this height, the execution of the program is brought back to the loop.

  in step S1 for a second time. On the contrary

  if the result is equal to zero or more, that is, if the actual value of the elevation height is equal to or less than the stored upper limit of that elevation height, then execution of the program proceeds to step S5. At this step S5, the comparison between the lower limit of the elevation height, which has been previously stored in the memory, and the actual value of this elevation height is again performed. In step 56, if the result is zero or more,

  that is, if the effective value of the elevation height

  is less than the lower limit of stored height

  In the memory or equal to it, the program execution is returned to the main loop in step S1 for a second time. On the other hand, if the result is "minus", the actual value of the elevation height will be greater than the lower limit stored in the memory and the execution of the program will then go to step

  57. In this step S7, the signal "memory OK" indicates

  when it is possible to store the data relating to

  the actual height of elevation, is transferred to the sub-pro-

  gram of memory. It is thus possible to store the

  their predetermined elevation height in the micro-

computer 230.

  FIG. 8 is a block diagram of a circuit making it possible to carry out the aforementioned command from the

  illustrated in Figure 7. As it was said before,

  previously, the elevation height counter 222 is provided in the interface circuit 220 shown in FIG. 1. In the present embodiment of the invention, the counter of

  elevation height 202 comprises three bidirectional counters

  222A, 222B and 222C. The first counter 222A counts

  the output pulses emitted from the sensor

  The central processing unit 242 performs a calculation based on the value so counted to produce a signal indicating the elevation height. The data corresponding to the height of elevation is displayed on the keyboard 246. To pre-establish the above-mentioned upper and lower limits, the second counter 10222B is provided to pre-establish the upper limit of the height of elevation, for example 2.8 m, and the third meter

  222C to pre-establish the lower limit, for example 8cm.

  A reset switch 222R is closed

  when the fork 18 is applied to the ground. As a result

  the first counter 222A is emptied and the lower and upper limits of the elevation height are

  respectively in the second and third

  222B, 222C. Then the operation of com-

  raising the height of the fork 18 to move this fork up and down. During this operation, the first counter 222A performs an addition count at the time of the elevation of the fork 18, for

  apply a rise signal Su to each of the terminals of

  IR subtraction tres of the second and third counters 25222B, 222C. Thus, a reduction is made in the second and third counters 222B and 222C. In the same way, when the fork 18 is lowered, the first counter 222A performs a subtraction count for

  to supply a descent signal SD at each of the terminals of

  in addition to the second and third counters 222B 222C. An addition is thus made in these second and third counters 222B, 222C. Consequently, when the value of the elevation height of the fork 18 becomes

  is located above the upper limit

  However, the output of the second counter 222B is "minus" to produce a logic output "1". On the contrary, when

  value of the fork lift height 18 is greater than

  below the stored lower limit, the third counter 222C delivers a "minus" output to produce an output

  logic "1". The output of the third counter 222C is inverted

  When the fork 18 reaches a position equal to or less than the stored lower limit, the output of the third counter 222C is "O". The output of this third counter 222C is inverted by the NO gate 224. As a result, the logic signal

  "1" is applied to the OR gate 226. Thus, when the furnace

  When the step 18 is in a position greater than the stored upper limit, or in a position equal to or less than the stored lower limit, either of the inputs of the OR gate 226 is at the "1" level. It

  As a result, this OR gate 226 produces an inhibit signal.

  MEM INH, even if the operator tries to

  memory in memory of a height value of elevation addressed to the microcomputer 230 from the keyboard 246, thus making it impossible to store a data relating to the

elevation height.

  According to the first embodiment of the invention,

  when the position of the fork 18 is beyond

  above the upper limit previously stored in the

  microcomputer 230, or even below the lower limit

  stored, ie when the fork 18 is not within the range of permitted heights of elevation,

  the establishment of data relating to the height of elevation

  in the memory is prevented. Therefore, the value stored in the microcomputer 230 by loading the elevation height data into the memory, in the unloaded state, is erroneously identified as being the value stored in the state. charge. Even if the automatic lift height control is performed with a forklift truck with a thick fork, only the fork 18 can occur.

  can not be lowered to the previous height of elevation

  already established, which makes it possible to ensure the automatic control of the elevation height in a manner

perfectly regular.

  We will now consider the second form of execu-

  of the present invention. This second form of

  tion has solved the problem that emerges

  that elevation speed control is performed by controlling a slave drive system to operate

  a lift cylinder. To better understand this

  In the second embodiment, the method for controlling the speed of elevation will first be described with reference to FIG. 9. This figure shows the first aforementioned actuator 322 which becomes active when it receives a signal d Sl command indicating an opening angle from the microcomputer 230. As previously indicated, the actuator 322 includes a drive motor 322M, transistors 322T1 through 322T4 and a clutch 322C. The angle

  opening of the first control valve 342 is deter-

  mined by correction signals S2 and S3 delivered to

  actuator 322. The lift cylinder 346 is controlled by an output signal S4 output from the first control valve 342. Therefore, the piston 346P is

  actuated to perform elevator height control

  tion. References 345T and 345P indicate an oil reservoir and a hydraulic pump, respectively. A circuit

  345D for the 345P hydraulic pump is con-

  staggered by any engine. With a built device

  In this way, the control of the speed

  levitation (or lowering speed), mainly in the low and mid-speed zones,

  in order to achieve a predetermined value, is achieved

  adjusted by adjusting the opening angle of the first control valve 342 via the drive motor

  322M and clutch 322C. The set value of the speed

  stored in the microcomputer 230 using the aforementioned data input means 246, such as a keyboard. The set value of the speed thus stored is compared with the actual value of the speed which is supplied from the elevation height sensor 102.

  signal of order Sl which indicates the value of the opening angle

  The valve corresponding to the difference resulting from the above comparison is applied to the actuator 322 to control the drive motor 322M. The opening angle of the first control valve 342 is then corrected by the correction signals S2 and S3 provided by the actuator 322. The lift cylinder 346 is actuated by the signal of

  command 54 so as to perform a control of the speed

elevation.

  With such a provision there is a time limit for

  response. After a correction signal for an increase

  toment speed was produced, it flows 10 millisecon

  or 100 milliseconds until the drive motor

  322M turns to open the valve, resulting in an effective increase in lift speed. A

  Another disadvantage is the following: the opening angle order

  of the valve for increasing the speed is continuously supplied to the 322M drive motor up to

  what the actual value of the rate of elevation attains

  the newly established set value for

  be the speed. In particular, in this case, in the zone where the opening angle of the valve is small, the speed variation as a function of the opening angle order of the valve is abrupt. Therefore, the rotational speed of the drive motor 322M increases sharply to open the first control valve 342 abruptly, which has

  for the effect that the lift cylinder 346 is lengthened rapidly

  is lying. When the actual value of the lift speed reaches the set point, the difference becomes zero. At the same time, when the stop command of the drive motor 322M is applied to the actuator 322, the motor 322M is

  stopped while being subjected to the action of a predetermined inertia

  completed. Consequently, the opening angle of the valve at this moment is greater, because of the inertia, at the angle

  corresponding to the set value of the elevator speed

  tion. As a result, the actual lifting speed is too high compared to the set value provided for this speed. Therefore, the balance between the speed detected by the elevation height sensor 102

  and the setpoint set for the speed is broken.

  As a result, a gap angle command S1 due to the difference having a minus polarity is issued from the microcomputer 230. This causes a reverse operation in the closing direction of the first one. control valve 342. From the moment when the stop command of the drive motor is produced, the speed of the lift cylinder 346 is progressively reduced by varying or oscillating in the plus and minus directions, the speed of elevation modified as a limit, and it reaches

  next, the predetermined elevation speed after listening

a predetermined time.

  As mentioned above, the disadvantages

  of the elevation speed control circuit

  the following are the following: there is an absence of

  stability and stability when placing an order for

  speed, as a result of the oscillation of the elevator speed

  when the setpoint is changed, in addition to the

response time.

  The second embodiment of the invention has

  to solve these problems in the manner that will now be described with reference to Figure 10.

  same numerical references indicate the corresponding elements

  therefore the explanation will be omitted.

  In the automatic control system of the

  A main loop for control of the lift speed is indicated by L1 and a secondary loop for the opening angle of the valve is indicated by L2.

  digital-to-analog converter 262A is intended to con-

  to turn a digital signal 56 provided by the micro-

  computer 230 into an analog signal S7 indicating the

  their setpoint for the opening angle of the valve. A

  comparison circuit 262B is provided to compare the

  S7 set point signal with a detected voltage of the servomotor drive circuit which will be discussed below. An amplifier 262C is provided to amplify the differential output signal S8 delivered by the amplifier circuit.

  comparison 262B. The 322M drive motor is powered

  depending on the amplified signal S9 provided by the amplification.

  262C. A potentiometer 322P cooperates with the driving motor 322M. The feedback signal from the potentiometer 322P is applied to the comparison circuit 262B. A gearwheel 342W is rotated through a clutch 322C. A 342L lever is attached

  to the axis of the gearwheel 342W. At this lever 342L are hooked

  First ends of two springs 34251 and 34252. The other ends of these springs 342S1 and 34252 are hooked to a fixed element not shown.A drawer or plug not shown, intended to open or close the valve and which communicates with the conduit 342C , is housed in a valve body 342V, this drawer or plug being connected to the

lever 342L.

  With the elevator height control device

  mentioned above, the digital order signal S6, supplied

  firing from the microcomputer 238, is transformed into an analog signal

  57 by the digital-to-analog converter 262A.

  This analog signal S7 which serves as a reference signal for the opening angle of the valve is applied to the comparison circuit 262B. The servomotor drive circuit 322 'is energized as a function of the amplified signal 59 resulting from the difference between the setpoint signal 57 for the valve opening angle and the feedback signal.

  S10. Thus the predetermined angle of rotation of the motor of

  322M stretch is fixed. In other words, when

  sistors 322T1 and 322T2 become active in accordance with the amplified signal S9 corresponding to the set point signal S6 for the opening angle of the valve, the drive motor 322M rotates forward. Conversely, when the transistors 322T3 and 322T4 become active, the drive motor 322M rotates in reverse. following

  the angle of rotation of the drive motor 322M, the le-

  342L is in turn rotated through

  322C clutch and 342W gear. Thus the opening angle of the valve is determined. It results

  that the speed of movement of the piston 346P of the lift cylinder

  346 is fixed. According to the speed of movement of the piston 346P, the pulse signal 55f emitted from the

  elevation sensor 102 forming a generator of im-

  pulses is applied to the microcomputer 230. The predetermined signal corresponding to the speed reference value is set in the memory 244 of the microcomputer 230. This microcomputer performs a comparison calculation between the effective speed of the piston 346P and the setpoint value of the speed, so as to transmit the digital order signal 56. The digital-to-analog converter 262A produces a voltage proportional to the

  command signal S6, to apply it to the comparison circuit.

  2628. In this comparison circuit is carried out a comparison between the voltage of the signal S7 and that of the reaction signal S10. The control of the opening angle of the valve is performed such that the output signal of the comparison circuit 262B serves as a control command of the secondary loop. Thus the control of the elevation height is performed in accordance with the above operation. The speed of the fork 18 is represented by the curves -el and e2 of FIG. 12, the symbol II indicating a characteristic curve in the unloaded state and the symbol e2 a characteristic curve in the loaded state. As we can

  see figure 12, the fork 18 is not raised

  for an opening angle equal to & o, even in the non state

  charge. For an opening angle of & 4, the elevator speed

  It is found in the full speed condition, in the unloaded state, while in the loaded state the fork 18 does not move at all. For an aperture angle equal to O max which corresponds to the maximum degree of aperture, the elevation speed is placed in the full speed condition, in the loaded state. For this reason, in the present embodiment of the invention, it is provided to divide the angle from So & max into multiple steps.

  for example 50 steps, to deliver a corresponding order signal.

  laying at the opening angle of the valve from the micro-

computer 230.

  FIG. 11 is a diagram illustrating an execution of the program of the microcomputer 230. When the signal S5f representing the value of the speed coming from the sensor 102 is reapplied to the microcomputer 230, during the step 51, it is determined whether the setting time of the timer has been exceeded or not. If the timer setting time has not been exceeded, the program execution is reset to

step S1 for a second time.

  If the predetermined time interval, for example -30 milliseconds, set in the timer is exceeded, the comparison between the actual speed and the target speed is performed in step S2. If the actual speed is not greater than the set speed, the execution of the program proceeds to step S3 to issue an order of increasing the speed of a step. When the actual speed is greater than the set speed, the execution of the program proceeds to step 54 to produce an order of speed reduction of one step. When the

  actual speed is equal to the set speed, the

  of maintaining the present condition is produced at the

  Thus, when the execution of the program in the steps S3, S4, S5 is completed, the reset operation zero of the timer is performed in step 56. Then the operation

  start of the timer is performed in step S7.

  The execution of the program is then brought back to step SI and

the same procedure is repeated.

  Program execution to compare the value of

  setpoint and the actual speed value in the micro-

  computer 230 has been exposed above. We will now describe

  Referring to FIG. 11, the operation of the elevation speed control device according to the invention.

  It will be assumed that the correction of the speed of

  is carried out under the condition that fork 18 is

  controlled at the predetermined elevation speed.

  When the speed detection signal 55f cor-

  the speed of movement of the piston 346P, which is provided by the lift height sensor 102, is applied to the microcomputer 230, the judgment relating to whether the predetermined period of time established by

  the timer has been exceeded or not, is performed in accordance

  to the algorithm shown in Figure ll.Then the comparison between the effective speed and the speed of

  setpoint is achieved. If the effective speed is lower than

  At the set speed, the microcomputer 230 generates the binary order signal 56 to increase the speed by one step. If the actual value of the speed is greater than the set point, the microcomputer 230 then produces the binary order signal S6 to decrease the speed by one step. If the actual speed is equal to the set speed, the microcomputer 230 produces the binary order signal S6 to maintain the speed. In digital-to-analog converter 262A, the command signal 56 which is a coded signal, for example from 0 to 50 as illustrated in FIG. 13, is converted to provide a signal of

  voltage corresponding to the aforementioned signal. This signal of

  sion serves as an angle S7 signal

  opening of the valve. As mentioned above,

  This signal S7 is applied to the secondary loop L2 as a control command. So the first valve 342 is-

  it's commanded and the elevation speed is correlatively

ordered this way.

  According to the second embodiment of the present invention, the subsequent correction signal is not increased or decreased by one step only as a result of the

  difference between the effective speed and the speed of con-

  sign, in a time interval of about 10 milliseconds

  of, determined by the timer, after the previous correction signal has been produced. Therefore, after

  that the correction signal has been produced and that it results

  then a change in speed as a result of this correction, the subsequent correction is made. This has

  Consequently, an excessive correction may be

  undermined. Moreover, since the adjustment step of the opening angle of the valve is sufficiently small, the angle of

  rotation of the 324 M drive motor is small for each

  that correction operation. Therefore, in the operation of stopping the drive motor 322 M due to a stop command which is produced when the speed reaches the set point, there is a slight possibility that an excessive rotation will occur. 322 M drive motor is produced as a result of the inertia. In addition, the pitch of variation of the opening angle of the valve is sufficiently small, which makes it possible to prevent the speed from changing abruptly. By

  therefore, this leads to a control of the height of

perfectly stabilized.

  We will now consider the third form of

  embodiment of the invention in which the elevation speed control device illustrated in FIG. 10 is used. The same references as those used in FIG.

  1 are assigned to the corresponding parts, the explanations

will be omitted.

  An automatic height control program

  elevation is stored in the microcomputer 230.

  When a pushbutton for starting the lift height operation is pressed, the microcomputer 230

  applies a control signal to the first control circuit

  of 262 (Figure 1) in accordance with the elevation height control program. The first control circuit 262

  apply a command order, representing the opening angle

  the valve, at the base of each of the transistors 322T1 to 322T4 constituting the servomotor drive circuit

  322, in order to perform an alternating command of the closed type

  open of these transistors. The drive motor 322M is thus controlled so that the first control valve 342

  is operated as in the aforementioned embodiment.

  As a result, the lift cylinder 346 raises or lowers the fork in accordance with the upward or

  descent of the piston 346P of the lift cylinder 346.

  The microcomputer 230 detects the height of elevation

  and the speed of the fork 18 from the pulses

  output from the elevation height sensor 102.

From this detected information, the microcomputer 230 executes a program for performing an automatic command.

tick of elevation height.

  However, in such an automatic forklift to which the microcomputer 230 is applied, if one tries to stop abruptly the fork 18 moving at high speed, while the height of the fork 18 is changed from a value to another then stopped at this

  the last value, it is very likely that the load 40

  on the fork 18 loses its general shape. As a result

  When the height of the fork 18 is changed, it may be necessary to reduce the speed in the case of a load 40 which can easily lose its shape. In such a case, it is

  necessary to carry out a continuation order of the

  hostess. There is some delay before the lift speed catches up with the set value determined by the speed command command supplied to the first control circuit 262 from the microcomputer 230. In addition, the actual speed is calculated from the frequency of the output pulses detected by the elevation height sensor 102, these pulses appearing whenever

  the fork 18 moves by a predetermined interval. This-

  during, the detection of the speed of elevation

  time. For this reason, there is a disadvantage in automatically controlling the speed immediately before the

target height.

  The third embodiment of the invention has solved this problem and will now be described with reference to Fig. 14 which shows an algorithm of automatic speed control immediately before reaching a target height. In the first step S1, the difference between the target setpoint Hs and the effective height Hc is calculated. In step S2, it is judged whether or not the height of elevation has reached the height.

- - - -. -t.

  setpoint target Hs. If the effective height of elevation has

  reaches the target setpoint Hs, the automatic control

  tick of speed is completed. On the other hand, if the actual lift height has not reached the target set height Hs, the execution of the program proceeds to step 53. The configuration of the data relating to the set speed SPs as a function of the value absoluteIHI of the difference

  between the set reference height Hs and the height effec-

  Hc is stored in the microcomputer 230. Examples of data configuration are indicated by (A) and (B) in the block 53. In step 53, the read operation of the setpoint speed SPs in accordance with FIG. Absolute value is achieved. Then, during step S4,

  the operation of reading the effective speed SPc is ef-

  fectuée. The effective lift height is calculated by counting the pulses that appear each time the fork moves a predetermined distance, and

  is obtained by means of the elevation sensor 102.

  their, effective speed is calculated by measuring a gap between the pulses. The time measured is as illustrated in FIG. 15A, this time ranging from the rising edge of a pulse of the pulse train (or the falling edge of this pulse) to the rising edge of the next pulse (or as far as on the descending side). The 2strain of timer pulses as shown on

  Figure 15B is obtained by a programmed timer.

  We will now describe, referring to the figure

  C, the procedure used to obtain the train of impulse

  timers. In the first place, during the first step S1, it is determined whether the state of the pulse train of the

  sensor 102 is or is not "1". In step 52, the o

  waiting period for a pre-determined period of time

  born, for example, a millisecond. In step 53, the

  count of timer pulses is advanced by one unit.

  Step S4 examines for the second time whether the

  The state of the pulse train is at this moment "1". The program illustrated by steps S2 and S3 continues to be executed

  until the state of the pulse train is "1". Lors-

  that the state of the pulse train is "1", as shown in step 55, the count value of the timer is calculated. This provides information for measuring time.

  The process carried out during step S4 of the algorithm

  The subject of Figure 14 has been indicated above. The remaining processing of the program executed according to the algorithm will now be described as follows: In step S5, the value SPc - SPs SPs is calculated. The execution of the program is then distributed as it is

  illustrated by step S7, in proportion to the difference

  this, under the effect of the order of distribution shown in the

  eg S6. When the difference is small (for example at most 10%), the order "maintain current speed"

  is produced as illustrated by step S71. Lors-

  that the difference obtained ranges from + 10% to + 20%, the order

  to reduce the speed of a step "(to reduce the opening angle

  of the valve by one step in relation to the actual opening angle

  ture) is produced as illustrated by step 572.

  A step is defined as being a gap obtained by evenly dividing the predetermined area of the opening angle of the lift valve into a plurality of steps.

  not as illustrated in Figure 13. Where the difference

  result is greater than 20%, the order "to decrease the speed by two steps from the current speed" is

  produced during step S73. When the difference is

  nude ranges from -10% to -20% or is greater than -20%, the orders "increase the speed of one step" and "increase the speed of two steps" are respectively produced, as well as indicated by steps 574 and 575. The program represented by the algorithm of FIG. 14 is executed by

  the microcomputer 230. The speed command signals cor-

  corresponding to steps S71 and S75 are applied by the middle

  230, the first control circuit 262 represents

  shown in Figure 10. After a period of considerable delay

  aunt illustrated by step S8, the execution of the program illustrated in Fig. 14 is repeated. When the order

  constant speed is achieved, the magnitude SPs represent

  14 is a constant value. The speed control command is produced, as shown in FIG. 14, as a function of the magnitude of the speed

effective SPc.

  As mentioned above, when the algo-

  As illustrated in FIG. 14, the actual speed is obtained by a timer programmed as shown in FIGS. 15A, 15B and 15C, instead of being calculated from the frequency of the output of FIG.

  sensor. Therefore, it is possible to detect fast-

  the actual speed. For this reason the tracking control in the automatic speed control system, immediately before reaching the target height, is carried out promptly as a result of the fact that the detection

  Elevation speed is performed quickly.

  The fourth embodiment will now be described

of the invention.

  In the aforementioned forklift truck as illustrated in FIG. 2, during the automatic control of the height of elevation, when the fork 18 has not reached the target height (target position), it happens that the control is interrupted and stopped according to the judgment of the operator. According to the prior art, such a stop operation is performed by actuating a button

  emergency stop or manual lever.

  However, when such a stop operation is controlled by acting on an emergency stop button or a

  manual lever, the shift operation of a drawer or wood-

  bucket provided in the first control valve 342, directly

  neutral position, is performed brutally. For

  this reason, the speed of raising or lowering of

  suddenly comes out nil or suddenly varies. As a result, an unwanted sensation appears and even the

  charge falls, resulting in a serious accident.

  The present invention has made it possible to solve these problems

  blemishes, as will be explained in what follows in

  referring to the attached drawing. In this form of execu-

  tion, the automatic elevation control device already used in the third embodiment is employed. Figure 16 shows an algorithm of a main program for automatic control of the

elevation height.

  During step 51, the absolute value HI of the difference between the target height (Hs) and the effective height (Hc) at which the end portion 18F of the forearm 18 arrives. During step S2, the value is determined. if the absolute valueIHI is zero or not. If the absolute value HI is equal to zero, the fork 18 is considered to have reached the target height. Therefore, as illustrated by step S3, the stop command of the drive motor is produced. When the absolute value is not equal to zero, it is determined in step 54 whether the absolute value HI is equal to or less than 50 cm. If the absolute value H greater than 50 cm, in step S5, the order of maintaining the current speed is produced. In step S5, if the absolute value HH is equal to or less than 50 cm, the execution of the program proceeds to step 56. In this step 56, it is determined whether the absolute value HI is equal to or less than 20 cm. If the absolute valueIHIis

  50 cm and over 20 cm,

  in step 57, the average speed command command signal, this signal being applied to the first control circuit 262. If the absolute value IHl is less than or equal to 20 cm, it is delivered, during the step 58, a low speed command command signal, for example of very low speed, this signal being applied to the first control circuit 262. Thus, the first control circuit 262 delivers the angle command signal of opening of the valve corresponding to each input signal and to transistors 322T1 to 322T4 constituting the drive circuit 322 'of the servomotor, in order to control the drive motor

  322M. So, as can be seen from the description

  previous, the first control valve 342 and the lift cylinder 346 are controlled according to the output of the drive circuit of the servomotor 322 '. During such automatic control of the height of elevation, while the fork 18 has not yet reached the target height, it may happen that it is necessary to stop the movement of the fork 18 according to the decision of the operator. In this case, it is good to stop progressively and slowly

fork 18.

  The operation of progressive stop of the fork is carried out as follows (command mode): I.- It is determined if the control is carried out at high speed, at medium speed or at low or very low speed; 2.- If the command is carried out at high speed, the order relating to the high speed is transformed into the average speed order 3.- If the command is carried out at medium speed, the order relating to the average speed is transformed into order of very low speed;

  4.- If the order is made at very low

  the movement stop command is produced or

  the sequence of continuation of the order

  matic. When the very low speed command is made immediately before the target height is reached, while an automatic command is made, this automatic control continues;

  5.- When the order is entered into the

  As a result of the progressive control of the drive motor, a) the drive motor is decelerated and stopped after a predetermined delay based on the following process: high speed - medium speed - T - very low speed - v stop (process mode change as a function of time); b) the order is made according to the conditions

  drive. For example, when the order is made

  killed at high speed, the target distance (target position)

  Hs is transformed into the distance that is obtained by adding

  both 50cm at the current position and the order is changed so that the command at medium speed is carried out. If the fork is within a distance of 20cm from the target target position, the order is changed so that a very low speed control is performed and the fork is stopped at the position visited.

  If, on the other hand, the order is made

  is averaged, the adjustment is made in such a way that the target position Hs is 20cm. Thus, the order is modified so that a very low speed control is achieved and the fork comes to stop in the target position (method of converting the control mode to function

distance).

  The methods defined above in paragraphs 1 to 4 and 5b will now be described with reference to Fig. 17. A subroutine for the progressive stop command, i.e., the method defined in paragraphs 1 to 4 and b, as shown in Fig. 17, are set in the main program stored in the microcomputer 230 and which is illustrated in Fig. 16. The microcomputer 230 is provided with a push-button switch 232B for

  the issuance of the progressive stop order. When applying

  on the pushbutton switch 232B, the order

  AP progressive stop in Fig. 17 is produced. The half

  the client determines, in step S1, whether the

  effective speed is high (VE) average (VM) or low (VB) or even very low, from the output signal of the elevator height sensor 102. If the speed is high (VE), the execution of the program go to step S2. During this step S2, the value 50cm is entered in the value of the target height (Hs) and the execution of the program passes to the main program for the automatic control of the

  elevation height. If the speed is average (VM), the

  execution of the program proceeds to step S3. During this step 53 a value of 20 cm is introduced into the value of the target height Hs and the execution of the program proceeds to the main program as illustrated in FIG. 16. If the speed is very low (VB), the execution of the program passes

  at step S4. During this stage S4, the main program

  the automatic control of the lift height

  tion, which is illustrated in Figure 16, is continued provided that the target height Hs is the same as the previous height. The microcomputer 230 then executes the

  main program for the automatic control of the

  Elevator on the basis of the progressive stop order

  shown in FIG. 17. The command-command signal cor-

  respondent is applied from the microcomputer 230 to the

  first control circuit 262. If it is assumed that the furnace

  Che 18 is being lowered, the end portion 18F of the fork 18 is thus completely stopped as shown in Figure 18A. If it is assumed however that the fork 18 is being raised, this fork 18 is stopped as illustrated in FIG.

  18A and 18B the symbols have the following meanings:

  vantes: EL elevation; AB lowering; ELVE elevation at high speed; ELVM elevation at medium speed; ABVE lowering at high speed; ABVM lowering at medium speed; VM average speed; VB low speed; V speed

  T time; IF soft stop switch closed.

  During the automatic control of the height of

  when the push-button switch 2328

  order to issue the progressive stop order, which is

  provided in the microcomputer 230, is closed, the microcomputer

  230 determines the distance required to stop the fork 18 according to the speed reached immediately before that moment. The deceleration operation is performed by gradually reducing the set speed until the fork 18 reaches the target height. At this time, the fork 18 is found to be completely stopped. In other words, speed control is done in a way

  until the fork 18 is brought to the

  Ret. Therefore, this eliminates any potential shock

  being caused by the stopping of fork 18. It is

  that there is no risk of the load falling.

  According to the present embodiment of the invention,

  tion, the progressive stop operation is performed by implementing the method defined in paragraphs 1 to 4 and 5b

  precedents. However, the present invention is not limited

  such a procedure. This stopping operation progresses

  sif can be executed by implementing the defined process

  nor paragraphs 1 to 4 and 5a. In this case, instead of adjusting and determining as a function of distance (steps S1-S4 and step S6 shown in Fig. 16 and steps 52 and 53 shown in Fig. 17) it is sufficient to use the adjustments and determinations

  according to the time. As an example, the operation will be

  fork lift 18. The procedure to be followed

  described below can also be applied to the

  fork as shown in the figures.

  18A and 18B, as a result of the actuation of the

  Push button 232B (IF), the microcomputer 230 issues a reduction order of one step of the speed reached immediately before that instant. The microcomputer also emits, after a predetermined period of time, an additional order of decrease of one step of the speed. The fork 18 is thus completely stopped. Since the control of the stop of the fork is made of a

  On a regular basis, it is possible to completely eliminate the shock

  when the fork is stopped suddenly. There

  therefore, there is no risk that the load will fall.

  It is clear from the foregoing description

  that the device according to the present invention has the following advantages:

  During an automatic control operation of the

  When a progressive stop operation is required, pushbutton switch 232B is pressed to issue the soft stop command. The shutdown operation is thus controlled by making good use of the speed reduction method.

  elevation that was reached immediately before the

  2328 (push button

  paragraph 5 (a) or the process of

  the speed of elevation as a function of distance (method explained in paragraph 5b), these methods being established in microcomputer 230. The appropriate setting of time and distance, at the time of use of the aforementioned methods, prevents any drop in the load,

  because of the progressive stop of the fork.

  In the programs illustrated in FIGS. 16 and 17, in which the method set forth in paragraph 5b is used, values of 50 μm and 20 μm are used as the target distances. However, the distance is not limited to such values. Depending on the situation of a load 40 placed on the horizontal portion 18H of the fork 18, the preselected distance of 50em and 20c can be modified in a suitable manner. The microcomputer 230

  can then adjust freely, based on this modified value.

  the speed of deceleration.

  We will now describe the fifth embodiment of the present invention which aims to stabilize the control of the speed of elevation. Automatic order

  the speed of elevation is effected by means of

  This automatic control of the elevation height, if the actual elevation speed is too high compared to the speed required for proper control of the elevation speed, is controlled by the microcomputer shown in FIG. command signal

  tending to close the first control valve 342 is

  plicated to the first control circuit 262, from the middle

  230. As a result, if the speed of

  effective detection detected by the elevator height sensor.

  102 is still high, the microcomputer 230 delivers a control signal for closing the first control valve 342. However, since the speed change as a function of the opening angle of the valve is

  very brutal, as illustrated by the characteristic curve

  Figure 19, if, for example, the corresponding order is

  At the opening angle of the valve 892 is produced, the fork is stopped. If this fork is thus stopped, the speed of elevation is too low and the microcomputer

  230 produces an order of acceleration (in the direction of

  opening of the valve). However, if the elevation speed becomes too high in a short period of time, the same operation is initiated, which results in that the speed variation can not be done in a regular manner and that it is difficult. to stabilize the elevation speed. The presently described embodiment has the following

  characteristic that, when carrying out an automatic

  the predetermined height of elevation, limits

  upper and lower are assigned to the order of opening

  servocontrol valve, such that the opening angle order of the valve is within the predetermined range and the function capable of supplying, at the first control circuit 262, a control signal

  for the opening angle order of the valve, which is

  to the drive circuit 322 of the servomotor controlling the first control valve 342, so that the opening angle order of the valve is limited in the range

  predetermined, is returned to the microcomputer 230.

  In the automatic control of the lift height

  According to the present embodiment of the invention, for example when performing a command at low or very low speed, the device is designed such that the speed command can be produced only between 0 min. . and e max. in terms of the opening angle order of the valve as shown in Fig. 19. In this figure, the opening angle of the valve is also divided into several steps indicated by 6 0 For example, the opening angle of the valve is divided into 50 steps. We will now describe the present embodiment of the automatic control of the following height of elevation

  the invention, with reference to an algorithm for the program

  Figure 21 shows the speed of elevation shown in FIG. 21 and the characteristic curve illustrated in FIG. 20 which shows the variation of the valve opening angle as a function of the elevation speed. In Fig. 20, the opening angle of the valve is divided into a plurality of steps, which allows the speed to be easily adjusted by increasing or decreasing it one step at a time. In Figure 20, it appears that the speed control zone

  average is superimposed on the low speed zone. The mic-

  computer 230 runs the pitch control program

  of elevation as shown in FIG.

  Computer 230 determines first, in step S1, whether the speed is average or very low. If the control is placed in the average speed control condition, the

  upper limit O Lmax. and the lower limit p Lmin.

  the opening angle of the valve (opening angle of the lift valve) are substituted for the upper limit

  S max. and at the lower limit Smin. the speed of

  This is illustrated by step 52. This establishes the operational speed control range. With regard to the very low speed control, the same adjustment is made during step 53. The comparison

  between the set speed and the actual speed (

  detected by the elevation height sensor 102) is performed in step S4. In step 55 is realized

  a check to determine whether an increase or decrease

  speed is required. When it is necessary to increase the speed, the opening angle of the valve is increased by one step. In step S6, it is determined whether the

  speed is located above the upper limit

  Smax speed. when you add a step to the angle

  effective opening. If the speed is higher than

  re to the upper speed limit Smax., we do not add a step to the effective opening angle, to maintain at its present value the opening angle of the valve (see step

  S9). If the speed is not greater than the upper limit

  speed controller Smax., a control signal of

  speed corresponding to the effective opening angle

  step (step SB). When the deceleration of the speed

  required, in step S5, the opening angle of the valve is reduced by one step. In step 57, it is determined whether the speed corresponding to the effective opening angle of the valve reduced by one step is less than the speed limit.

  lower Smin. If this reduced speed is lower

  below the limit Smin., the speed control signal of the actual opening angle of the valve is maintained (see step S9). If, on the other hand, the reduced speed of one step is greater than the lower speed limit Smin., The speed control signal is reduced again by one step.

  as regards the effective opening angle (see

  eg S10). In step 55, if the actual value of the speed is equal to the value of the set speed, the actual present signal corresponding to the angle order

  opening of the valve is maintained.

  Thus, the speed command command signal

  corresponding to one of the steps 58, 59 and S10 of the algorithm

  theme of Figure 21 is applied to the first circuit of

  command 220, from the microcomputer 230, for

  kill a speed command from the automatic command

tick of elevation height.

  The program for the speed control is stored in the microcomputer 230 as follows: when performing a command at medium speed, the upper limits C Lmax are set beforehand. and lower 0 Lmin. the opening angle of the valve (opening angle of the lift valve 342) respectively corresponding to the

  upper limits Smax. and lower Smin. speed.

  The microcomputer 230 delivers a command command signal

  speed applied to the first control circuit 262

  in accordance with the algorithm shown in FIG. 21, so that the opening angle of the valve is within the aforementioned range of variation of the angle. The same order is made with respect to the order to

low speed.

  As is evident from what precedes

  because the control device of the lift valve

  A prior art fork does not establish the opening range of the lift valve when adjusting the speed, this speed is too high or too high.

  low when it is outside the predetermined range.

  As a result, it is difficult to adjust the speed and

  this has the consequence that the latter becomes unstable.

  On the contrary, according to the present invention, the range of

  Elevator valve adjustment is limited to the pre-set range.

  determined. Therefore, the variable speed range

  the actual lifting is narrowed according to the limita-

  adjustment range of the lift valve. As a result, the last form of execution mentioned above makes it possible

  stabilize the elevation speed.

Claims (14)

  l.- Control device for a mechanism of   loading and unloading adapted to be   in a forklift truck, comprising a detection unit (100) having at least one elevation height sensor (102) for measuring a fork elevation height (18), said elevation sensor 'elevation   (102) producing a proportional output pulse signal   at the elevation height, a control unit (200) responsive to the output of the detection unit 100 (100), which control unit (200) calculates on the basis of the output signal of the detecting unit and producing a predetermined control signal as a function of   the calculated value, and a training unit (300) replies   to the predetermined control signal of the communication unit   command (200), this training unit (300) delivering a training output signal so as to vary the   lift height of the fork of the truck, is characterized   in that the control unit (200) comprises an interface circuit (220) for receiving the input signal from   of the detection unit (100), as well as a general circuit   controller (240) comprising a memory (244)   to store data relating to a height of elevation   predetermined manner and data inputting means (246) for supplying data to the memory, and in that the control command generating circuit (240) produces a control command from a comparison calculation between the output of the detection unit (100) supplied through the interface circuit (220) and the relevant data stored in the memory (244), for performing a control of the   y3 desired elevation height in accordance with the order of com- mande.   2. Device according to claim 1, characterized   characterized in that the interface circuit (220) is provided with an elevation counter (222) for counting the   pulse signal output from the sensor Elevator (102).   3. Device according to claim 1, characterized   in that the drive unit (300) comprises a   electrical converter / hydraulic pressure (320) responds   to the output of the control unit (200), and   a hydraulic pressure drive unit (340) replies   at the output of the electrical converter / hy- hydraulics (320).   4. Device according to claim 3, characterized   rised in that the electrical converter / hydraulic pressure   It consists of an actuator (322) comprising a   drive circuit of a servomotor producing a   indicating an opening angle of a valve.   5. Device according to claim 4, characterized   characterized in that the hydraulic pressure drive unit (340) comprises a control valve (342) responsive to the output of the drive circuit of the servomotor (322), and a lift cylinder (346) hydraulically controlled by the valve control (342).   6. Device according to claim 4, characterized   in that the control unit (200) further comprises a control circuit (262) responsive to the difference between the control command supplied from the production circuit   control commands (240), and the feedback signal from   of the servomotor drive circuit (322) to control the servomotor drive circuit (322)   7. Device according to any one of the   prior art, characterized in that the circuit (240) producing the control commands comprises means for preventing storage, in the memory (244), of the data   relative to the height of elevation, when the relative   the actual lifting height, which is detected by the elevation sensor (102), is greater than the preselected upper limit or lower than the   preselected lower limit.   8. Device according to claim 7, characterized   in that these means comprise a first bidirectional counter (222A) responding to the output of the sensor of   height (102), a second bidirectional counter   (2228) to pre-establish the preselected upper limit   and which responds to the output signal of the first   bidirectional transmitter (222A), and a third bidirectional   recalibration (222C) to pre-establish the lower limit   selected and which responds to the output signal of the first   bidirectional counter (222A), storage, in the memory   re (244), of the data relative to the height of elevation being pocketed by one or other of the outputs of the second   and third bidirectional counters (222B, 222C).   9.- Device according to any one of the   1 to 6, characterized in that the circuit (240) producing the control commands produces a control command signal divided into a plurality of steps according to the elevation speed signal detected by the height sensor. elevation (102).   10.- Device according to any one of the   prior art, characterized in that the circuit (240) producing the control commands compares the setpoint value for the elevation height with the value of the actual elevation height detected by the elevation height counter (222). in a predetermined interval after this last value has been applied to it, and then produces a control command signal divided into several steps.   11.- Device according to any one of the   1 to 6, characterized in that a data configuration representing the variation of the set value for the elevation speed as a function of the absolute value of the difference between the target elevation height and the elevation height effective is stored in the memory (244) so that the circuit (240) producing the control commands issues an order which is a function of the difference between the set value for the elevation speed obtained from said data configuration and the   value of the actual lift speed.   Device according to Claim 11, characterized in that the value of the actual lifting speed is obtained by counting, by means of a timer   programmed, the number of pulses of this timer appears   between the output pulses provided by the   lift height sensor (102).   13.- Device according to claim 6, characterized   characterized in that it comprises a button switch-   pushbutton (232B) to gradually stop the motor   flow (322M) so that the circuit (240) producing the control commands transmits a deceleration command which is a function of the speed of the fork (18) immediately   before the push-button switch (232B) is   on the basis of a predetermined time or predetermined rate.   14. A device according to claim 6, characterized   in that the circuit (240) producing the control commands issues an order to limit the opening angle   a control valve (342) at a determined range.