FR2610559A1 - APPARATUS FOR DISMANTLING PARTS - Google Patents

Abstract

THE INVENTION CONCERNS AN APPARATUS FOR DE-MAGNETATION OF PARTS. IT RELATES TO AN APPARATUS INCLUDING MAGNETIC TRANSFORMERS 50 AND DE-MAGNETIC TRANSFORMERS 52 INTENDED TO ENSURE THE RETENTION OF A PART ON A MAGNETIC CHUCK. PHOTO-EMISSIVE DIODES ARE ASSOCIATED WITH RESISTORS WHICH CAN BE CIRCUITED SO THAT THE HOLDING FORCE IS ADJUSTABLE IN DIFFERENT MODES, ALLOWING THE APPLICATION OF A MAXIMUM FORCE OR A VARIABLE FORCE OR THE RELEASE OF A PART . APPLICATION TO GRINDERS.

Description

The present invention relates to a method and a

  demagnetization apparatus.

  More specifically, the invention relates to the field of demagnetization of parts that have been magnetized, so that they can be used later. These parts may have been magnetized either deliberately or inadvertently during another operation but, to be used as parts, they must be demagnetized. Whether deliberately or inadvertently magnetized, the operation of the apparatus according to

  the invention is the same, but the domain of disarmament

  has reached a degree of elaboration so

  much of it applies to parts that have been deliberately

  lovingly. The most important example of this situation is a grinding or grinding machine in which parts are held by a magnetic mandrel. The parts thus retained are deliberately magnetized and, after rectification, the magnetization force is removed. There remains a magnetism in the pieces as well

  in the chuck, and a desir-

  to suppress this residual magnetism.

  This general area has been highly developed, and development to this stage involves various phases

  or various modes of controlling the holding force of the

  gnotism that keeps the pieces on the mandrel, and the subsequent phase of demagnetization. In these different phases and modes, different levels of sustaining force are used, including levels that are known as "peak", "variable" and "residual". Each of these phases has a particular purpose, but is obviously used individually, none of them being used in combination and, in general, in a grinding operation, it is necessary that the holding force can be

  well set at different levels. A fourth mode

  ration "is also used to demagnetize the piece

  and his release from the sustaining forces.

  So far, the various levels of the sustaining force during these demagnetization operations have

not been well regulated.

  In the application of the invention to

  the device not only regulates the demagnetization but also controls the chuck, and the device

  can therefore be called a mandrel control device.

  Although the device is particularly applicable to

  grinding machines, it is also suitable for other phases of

  mantation. The invention therefore relates generally to a

  new process and apparatus for regulating and

  set an order for setting the hold and the demagnetization

  of parts in a control operation of a mandrel.

  A more particular object is the production of an apparatus and a method particularly suited to a grinding machine, in which various phases of the forces

  Magnetics are used, and with the characteristics

following benefits and advantages:

  1. a new and effective security feature

  rity is used as a solidarized action that prevents accidental movement of the mandrel

  from one phase of the sustaining force to another.

  2. The invention facilitates the adjustment maneuver of the holding forces, ensuring the retention of parts in the

  grinding machine, and thus accelerates the associated grinding operation.

fication.

  3. The invention implements new indica-

  controllers of the controlled operating steps (rectification

  tion) and the implementation of the various steps.

  4. The invention can be easily incorporated into the overall electrical controls usually incorporated in the machine in which it is operated, by

example of a grinding machine.

  Other features and advantages of the invention

  tion will become more apparent from the following description,

  with reference to the accompanying drawings in which: Figure 1 is a simplified elevation of a grinding machine in which the demagnetizer of the invention is used;

  FIG. 2 is a diagram showing the device

  FIGS. 3 to 7, which together form a diagram

plet of the apparatus; and

  FIGS. 3 to 7 together represent the differences

  parts of the circuit of the apparatus according to the invention.

  To better consider the nature of the invention,

  It should be noted that a demagnetization operation

  that necessarily a magnetization. In the application of the demagnetization apparatus to a grinding machine as previously indicated, the parts being held on the table by a magnetic mandrel, the mandrel and the parts themselves are magnetized. When the parts have to be released, the magnetic holding force is removed, but the residual magnetism indicated above is usually very important and this residual magnetism must be removed so that the parts can be removed

  mandrel. The operation is carried out in the phase of

  tation; in this phase, the piece is magnetized repeatedly, that is to say that it is magnetized according to a series

  reverse steps successively or with polari-

  opposed, and the voltage is reduced at each step and,

  in the last step with the last inversion, the magnet

  is usually nil or nearly so. Thus, the demagnetization operation comprises these magnetization steps, and

  the entire magnetization phase is controlled and executed

  cut by the demagnetization or control apparatus

mandrel according to the invention.

  The different levels of magnetic force

  holding the parts in place on a grinding machine, are used

  in the various stages of a rectification operation.

  tion. These steps have been developed in coordination with the development of demagnetization devices and have been

  currently made possible by the important development of

  both demagnetization devices. In a grinding operation, it is obviously necessary that the parts are firmly held in place, and the "maximum" setting gives the great holding force necessary for actual grinding. This "maximum" level may have different values in different grinding operations, but in any grinding operation it has a value

  predetermined and does not exceed this value.

  The "variable" phase is used to maintain

  parts with different characteristics, in opera-

  different types of rectification. It also happens that some parts, because of their characteristics such

  that their shape or lack of mechanical resistance, must

  may be restrained by a lesser force. These different types

  parts should be selected on the basis of their

  in each individual operation of rectification

  tion, and these forces may be different in

  successive rations of rectification. For example, a

  piece can be hollow and is placed on

  with a concave face down and, if a large holding force was applied, it would cause deformation or curvature of the workpiece and, in this case, as in many other cases,

  maintenance is used so that it does not distort the part.

  Although, in this case, a lower rectification force must be used, this is tolerable because of the non-deformation criteria. The device is of a type such

  that it allows a setting at different selec-

  in "variable" mode, these values being lower than those of the "maximum" mode, depending on the characteristics of the rectified part in each individual operation.

of rectification.

  In another step of the grinding operation, it may be desirable to remove a single piece of

  chuck to check the grinding, before grinding

  complete, and to put it back in place for the

  Following the rectification operation, this surrender

  place to exactly correspond to the previous position

  toothed. In this step, only the first part must be removed and not the others and the holding force is reduced to the "residual" value so that this part can be removed. This "residual" force is sufficient for it to maintain the parts in their original position in the absence of any other external force. After performing this verification operation, the part is put back in place and the device is again

  "maximum" or "variable" setting, and the rectification operation

cation continues.

  When the entire rectification has been completed

  the device is set to "release" and, therefore,

  quence, the demagnetization operation is performed. This step is described in detail and it is not necessary to describe it for the moment, but the resulting effect is the reduction of the holding force to a zero or almost zero value so that the part can be released from the mandrel. . Reference is now made in detail to the drawings; FIG. 1 shows a grinding machine 12 of known type having

  a table 14 which moves longitudinally in transla-

  in the horizontal direction as indicated by the double arrow 16, and the workpiece, bearing the reference 18, is placed on the table and is held there by a magnetic mandrel 20 incorporated in the table. A wheel 22 works in a vertical slot 24 and is lowered in contact with the workpiece so that it performs the grinding operation when the workpiece moves in translation below.

  the wheel under the control of the table.

  We now refer to the electric circuit; FIG. 2 represents the arrangement of FIGS. 3 to 7 and

  it should be noted that mandrel 20 and part 18 are

  at the bottom of Figure 3.

  As a matter of convenience for the consideration of the different parts of the circuit shown in the various figures, reference is made to the mixed lines which separate the circuit parts and the conductors which have been cut are identified on both sides of the cutting lines so that the adaptation is facilitated. The parts of each driver that are cut carry the same

  references on both sides of the cut line and the references

  are used throughout the circuit description

  electric. The vertical line 7 of cut separates the figures

  3 and 6 and the cut conductors are designated individually.

  7a to 7c. The vertical cut line 8 separates FIGS. 4 and 5 and the cut conductors

  this feature are individually designated by the references

  8a and 8b. The vertical line 9 separates FIGS.

  and 7 and the cut drivers are designated individually

  9a to 9h. The horizontal line 10 separates FIGS. 4 and 6 and the conductors which it cuts bear the individual references 10a to 10d, with also

  the driver 10e between FIGS. 5 and 6. The horizontal line

  zontal 11 separates figures 5 and 7 and the drivers it

  section individually refer to 11a to 11d.

  The circuit comprises a power supply circuit 26 shown in FIG. 3 and a control circuit 28 shown in FIGS. 4 to 7. The circuit comprises a source 30 of alternating current connected to a transformer.

  32 of power, with leads 34, 36, 38 and 40

  binding the power transformer to the mandrel 20.

  The power supply circuit 26 includes the secon-

  certain magnetization transformers, the trans-

  complete trainers being incorporated in Figure 4. Each transformer has a primary and two secondary, together forming a game, and they form a magnetization game 50 and a demagnetization game 52. For the identification of the transformers, the primaries are designated with the same main numerical reference, followed by the suffix P while the secondary ones have the same main numerical reference but the suffix S and additional suffixes 1 and 2. These transformers have the role of adjust the current flowing from the power transformer 32 to the mandrel 20 and they work in cooperation with

  thyristors 56, 58 (FIG. 3). Thyristors 56 are desirably

  Each of them is individually identified by the references 56A, 56B and is associated with the secondary 50S respectively, and likewise the thyristors 58 are designated individually by the references 58A, 58B and are associated with the secondary 52S during operation. During the excitement of the secondary

  S, 52S as described in the following, these secondary

  conduct the thyristors 56, 58 in the conductive state and regulate the current flowing from the power transformer 32 to the mandrel 20. The set of transformers 50 is used to hold the workpiece on the mandrel in the grinding operation, and both games are used during

the demagnetization operation.

  Thyristors, transistors, rectifiers, bidirectional switches and gates

  can be called generically "valves".

  Reference is made to the control circuit of FIGS. 4 and 5; a main or control transformer 60 is powered by the AC source. The control circuit 28 also comprises (bottom of FIGS. 6 and 7) a switching device 62 comprising four individual "release" 62A, "residual" 62B, "variable" 62C and "maximum" 62D switches; the power circuit also comprises a potentiometer 64 (lower right part of Figure 7) having an arm 65. The individual switches 62A, 62B, 62C, 62D are manually operated individually according to the function to be filled as indicated by the names associated with them and, as indicated above, during the

  various stages of rectification and subsequent operations

  associated setting rules, including demagnetization

and partial demagnetization.

  Two full wave bridge rectifiers 70,

  72 (Figure 4) start from secondary 60S, the first to

  a trigger circuit 74 and the second one a

  76 of direct current. A pilot circuit 78 of dot and bar pattern (FIG. 5) of known type is incorporated in the control circuit and has an input pin 80, number 5, and a series of pins 82, numbers 1018, and a pin 84, number 1, at a reference position. Pin # 1 is

  connected to an adjusting resistor 86 and the other pins

  They are connected to setting resistors 88, these resistors being connected to a common conductor 90 joining the conductor 8d.

  Driver 8a is a common driver appearing

  all of Figures 4 to 7; of Figure 4 (upper right), it goes to the left and down in this figure; it goes from this position of figure 4 on the right in figure 5 and goes down then goes on figure 7 where it goes down to the left and goes down on the left on the

figure 6.

  The potentiometer 64 (lower right portion of FIG. 7) is connected at its low value end, at 91, to a conductor 9j and to the common conductor 8a and is connected, at its high value end, at 93, to the conductor 9i. When putting into operation the grinding machine and the apparatus according to the invention, the operator,

  in an initial step, turn off the power switch

  alternation 30 (Figure 3) and maneuvering the switching device 62 (lower part of Figures 6 and 7) according to the desired mode. For the "maximum" mode, it closes the switch 62D (FIG. 7) so that the pin n 12 of the toggle chip 94 (middle part on the left of FIG. 7) goes to a low level. Then, the transistor is turned on and, via a

  conductor 95 ', a digital switch 96, a conductor

  96 ', a digital switch 97 which is then closed, a conductor 11b and the conductor 97' (Figure 5) and the driver circuit 78, a positive voltage is placed on the pin n 5 of the driver circuit. This tension is

  continuous type and its value is determined by the

  voltage tester 76 which operates at approximately 12 V.

  This shows a negative or low voltage

  calves 4, 7, 13, 14 of the pellets 96 "and 96" '(half

  5) and spindle 4 of the wafer 97. Simultaneously, a high level signal appears at the complementary output pins 3, 9, 12, 15 of the wafers 96 "and 96" and at the spindle. No. 3 of the chip 97. This high level signal is applied to the bases of the pads 97a and 97b and the transistor 98 ". The 96 ", 96", 97 ", 97a, 97b pellets have four NPN transistors incorporated in each chip When applying the high level signal to the bases as indicated above, the transistors

  pellets 97a, 97b and 98 'become conductive.

  This puts the resistors 86, 88 and 98 'in circuit and the

  capacitor 103 (FIG. 4) is charged to its greatest vi-

  This allows the transmission of a maximum DC signal in the case of the set of magnetization transformers 50. The conductor 97 'comprises a capacitor 98 (upper part of Figure 5), the capacitor being mounted across the potentiometer 64 (Figure 7) on one side by the aforesaid elements 97', 97, 96 ', 96, 95' , 95, 94, and the other side through the conductors 8a and 103 '(lower right portion of Figure 7), in parallel with a transistor 100 (top of Figure 5) in a set 99. The capacitor 98 and the set 99 ensure

  a linear decrease in demagnetization steps.

  During the operation of the pilot circuit 78, following the application of a voltage to the input pin n 5, some of the resistors 86, 88 and 98 "are switched on, which corresponds to the internal function of the circuit If no voltage is applied to pin 5, none of the resistors are in circuit and, when selectively increasing levels of voltage are applied, the number of these resistors that are put into circuit is high and the higher the voltage of

  output is high. The circuit thus established through

  pilot circuit 78 provides the voltage regulation

  continuous output applied to the magnetic chuck.

  A voltage of suitable value, 12 V in this case, is transmitted by the transformer 60 (top of Figure 4) through the rectifier 72 to the terminals 91, 93 of the potentiometer 64 (lower right part of the figure

  7) through the described circuit elements

  previously and, depending on the setting of the potentiometer, a corresponding level voltage is transmitted to the control circuit 78. Depending on the number of resistors 88 which are in circuit, according to the predetermined voltage applied, a

  corresponding output voltage is applied to the

  103 (middle upper part of Figure 4) in the output lead 90 (8d) (middle upper part of Figure 5). A zero crossing detector 104 (upper left part of FIG. 4) comprising transistors, causes transistor 108 to conduct each zero crossing of the assembly 104. This discharges the capacitor 103 and triggers a delay or a sequence of synchronization

phase.

  This phase delay is obtained thanks to the time constant RC which is determined by the value of the capacitor and the number of resistors 86 and 88 switched on by the assembly 78. A transistor assembly 110 is associated with the capacitor 103 and comprises transistors 112,

  114, and the voltage across the capacitor 103 is

  controlled by the transistor 114 and, when the voltage of the capacitor 103 rises above the reference voltage determined by the transistor 112, the transistor 114 is at

  the conductive state. In the cycle of "liberation", the de-

  voltage growth in the capacitor 103 determines the DC output signal, while the decrease in the

  capacitor 98 determines the overall time of the cycle of

  mantation. The transistors 112, 114 are arranged

  However, any variation in voltage in transistor 114 caused by temperature variation is compensated for.

  by a similar variation in the transistor 112.

  Another transistor 116 forms a buffer for the

  the output signal of the set 110, this signal being different

  Reacted by a capacitor 118, and the setting of the value of the capacitor 118 increases or decreases the width of the trigger pulse that occurs at the output of a NAND gate 120. This NAND gate 120 is connected. enter

  NAND-associated gates 122, 124, associated with trans-

  respective trainers 50, 52 indicated above. The

  NAND gates 122, 124 are validated and excited alternately

  according to the operation of a CMOS oscillator chip 125 (lower left portion of FIG. 4) and elements controlled by its output signal. The NAND gate 122 controls the transformer 50 which acts as a holding transformer in the holding operation of the grinding machine while the two transformers play.

  alternately a role in the demagnetization operation.

  Other sets 126, 127 with transistors are associated with the respective transformers 50, 52, the first set

  comprising transistors 128, 129 and the second of the transistors

sistors 130, 131.

  Referring again to the patch 125 of oscillator

  (Figure 4), whose role is to regulate the operation of

  demagnetization; the following description relates to the steps

  demagnetization or inversion, and it does not depend on the value of the voltage used in the

  trip circuit 74 (FIG. 4). As noted above

  62D is used to put the apparatus in the holding phase and, after closing this switch, a negative electrical signal is taken from the common conductor 8a and is transmitted to a set 134 (lower part of the figure). 4). This set includes NAND gates 135, 136 and joins the base of transistor 142. The signal turns transistor 142 to the conductive state and enables or excites NAND gate 122 which causes conduction of transistors 128, 129, and the transformer is energized and remains energized as long as the control is in "variable" or "maximum" mode. The transformer 50 serves to maintain the excitation of the secondary 50S1, 50S2 (see also Figure 3), and the power applied to the chuck

  20 as indicated again below.

  The CMOS oscillator chip 125 and the associated circuit comprise another transistor 144 (middle of FIG. 4) and three NAND gates 146, 148, 150 (lower part of FIG. 4), the first being associated with the transistor 142 , the second transistor 144 and the third being associated with an RC network 152 which controls the CMOS oscillator chip 125 and a capacitor 155 and resistors 156, 157. The RC network also includes a sliding switch 153 which directly controls the chip 125 oscillator and allows through it

  the high, medium and low speed settings of

  DC voltage applied to the mandrel. This sliding switch is associated with resistors 157b, 157c intended to

  to be respectively connected to the network according to the posi-

  slip switch so that it determines the

  corresponding speeds during inversions.

  When the potentiometer 64 (lower part of FIG. 7) deviates from 0, the resistors 86, 88 and 98 "are switched on one by one, starting from the resistor 86 and, towards the right, verses resistors 88. In fact, this varies the charging speed of the capacitor 103 (upper part of FIG. 4), and directly adjusts the output signal and allows its variation from a minimum value to a

  maximum value corresponding to the chosen setting of the

  tiometer. This places a corresponding maximum load, of lower value, in the holding transformer 50 which itself retains the parts on the mandrel with a

  corresponding lower force, as indicated above

  ment, so that a deformation of the parts that could be

  due to a greater holding force is eliminated.

  When the device has to go into the demagnetization operation, it is set to "release" mode; the "release" switch 62A (lower part of FIG. 6) is closed and consequently the pin n 1 of the chip 163 (left part of FIG. 6) goes to a high level, the pin n 2 goes to a low level and actually opens the digital switch 96 (upper part of Figure 7) and disconnects the potentiometer 64 (lower part of Figure 7), the pin n 11 of the door 165 (upper part of Figure 5) passes to a high level and closes the digital switch 167 (upper part of

  FIG. 5), so that the capacitor 98 can be discharged

  ger. In this way, the voltage at pin 5 of the circuit

  bake 78 decreases slowly and also causes a reduction of the continuous output signal of the capacitor 98. In this step, the resistors 160 (lower right part of Figure 7) controlled by the manual switch 158 are switched on, the switch can to be moved selectively to three positions for this purpose as shown in solid lines for a position and in

  mixed lines for each of the other positions. These resistances

  are identified individually by the references a and 160d, they are connected in parallel with an associated resistor 160c (upper left part of FIG. 5) and increase the discharge rate of the capacitor 98. In the slow discharge position, only the resistor 160c is in circuit, in the medium discharge position, the resistors 160c and 160a are in circuit and in the fast discharge position, the two resistors 160b and 160c are in circuit. Simultaneously, the pad 125 of the oscillator (lower left part of FIG. 4) is enabled and reverses the polarity of the continuous output signal transmitted to the mandrel 20 (lower left part of FIG. 3). When the resistor 86 (upper part of Fig. 5 is switched off the circuit, the conductor 11a from the chip 96 "(central part of Fig. 5) goes high and causes a high level of the output signal to pass the door (upper part of Figure 7) to pin n 4. This turns the potentiometer 64 on (part

  bottom of Figure 7), and the "variable" or "maximum" mode

  wrong "can then be chosen and implemented.

  It should be noted that the possibility of adjusting the duration of the overall cycle of voltage reduction and adjustment of inversions is independent. This allows greater precision and gives great convenience in the

  parts with different hardnesses and configurations

  and other factors affecting the demagnetization operation. In this demagnetization operation, following the closing of the "release" switch 62A, the capacitor 155 (lower left part of FIG. 4)

  and the resistances 156, 157 determine the overall frequency

  while the switch 158 (lower right portion of Figure 7) provides fast, medium or slow discharge of the capacitor 98 which determines the duration of the "release" cycle. The output signal of the n-6 oscillator chip 125 is applied to a first input of the NAND gates 148, 146 and to the clock input 172, pin n 3 (lower right portion of FIG. ) of the rocker 162. The output signals of the unit 162 validate or invalidate the NAND gates 148, 146 and thereby turn the conductive or non-conductive

  transistors 142, 144, according to the cycle in question. The tran-

  sistor 142 allows the operation of the NAND gate 122 while the transistor 144 allows that of the NAND gate 124. We now refer to the "variable" mode which, as previously indicated, allows the maintenance of the parts

  on the mandrel with a force less than the maximum force

  In this "variable" mode, the arm 65 of the potentiometer 64 (FIG.

  predetermined position which, in the example considered, cor-

  three quarters of the "maximum" value as

  the implementation of this mode is ensured by closing the "variable" switch 62C by the operator (lower right portion of FIG. 6) so that pin 10 of the rocker chip 94 (Middle left part of Figure 7) has a high level and the pin n 12 of this pellet is also set to a high level, given the internal nature of the pellet, and the pin n 12 which is at a level High sets transistor 95 to the non-conducting state with opening of the "maximum" mode circuit from the high level point 93 of the potentiometer. Simultaneously, the signal

  high level closes terminals 8 and 9 of the digital switch

  173. This allows potentiometer 64 (the lower

  7) to adjust the voltage applied to pin n 5 of the driver circuit 78 (lower portion of

Figure 5).

  According to another explanation of the action of the transformers 50, 52, while the transformer 50 for example is excited under the control of the NAND gate 122, the set of secondary magnetization 50S1, 50S2 (Figure 3) is powered so that the thyristors 56 conduct, and the circuit is closed between the power transformer 32 and the mandrel. In this mode or in this phase, each time the transformer 50 is energized, the mandrel is powered and this applies both to the maintenance and

demagnetization.

  In alternate intervals in which the

  transformer 52 is excited in the mode or phase of desertion.

  the secondary 52 of the demagnetization game are excited and cause the conductive state of the

  thyristors 58, with closing of the circuit between the transformer

  32 power meter and chuck.

  -In the case of transformers 50, 52, it is necessary

  note that the secondary ones are opposed so that they

  they know a complete rectification of the current and the application of a constant power of maintenance in the mandrel. Correspondingly, each set, i.e., the magnetization set and the demagnetization set, during the demagnetization phase or mode, operates in corresponding intervals determined by the triggering and triggering circuits. oscillation indicated above and

  as described in more detail later.

  The "residual" mode is implemented by closing the "residual" switch 62B (lower part of FIG. 6) and the pin n 12 of the rocker pad 174 (middle of FIG. 6) changes to a low level. The signal from this step is applied to the pin n 2 of the gate 120 (middle of Figure 4). This interrupts the trigger pulses which no longer appear at the output, at pin n 3 of this gate, ie there is no continuous output signal flowing in units 126, 127 to transistors to transformers

respective 50, 52.

  The effect of this phase is the reduction of the holding force to a level such that a part can be removed for example to be tested, and the remaining parts are held in place, in the absence of additional external forces tending. to dislodge them. After

  these tests, the removed part is put back in place and the

  maintenance status is restored to the desired level, as

"maximum" or "variable".

  The apparatus includes a device for indi-

visually check the individual steps during the demagnetization phase. For this purpose, a pilot circuit 176 points and bars is arranged (lower part of Figure 7). This pilot circuit with points and bars is identical to the unit 78 (lower part of the figure); the pins n 5 are interconnected, that is to say that a conductor 9k (lower left part of Figure 7), passing through Figure 6, joins the stud n 15 (lower left part of Figure 6) of the control circuit 78 (Figure 5), and pin n 5 is also connected to pad n 15 (central lower part of Figure 5). When the voltage increases at the pin n 5, the resistors 86, 88 (upper right part of FIG.

  in circuit and, simultaneously, the first photo diode

  emissive 178 (bottom of Figure 7) lights up from the

pin n 1.

  The pilot circuit 176 at points and bars comprises

  light emitting diodes 178 shown schematically.

  The first light emitting diode, when illuminated, indicates the first power level and, when the voltage increases further, the other resistors 86, 88, 98 "(upper right portion of FIG.

  one by one, and the corresponding light emitting diodes

  each level of power. As a result

  quence, when the signal - continuous output increases at

  from the beginning, the diodes light up and indicate the

  when all diodes are illuminated, the "maximum" mode is established whereas, when only some are illuminated, a "variable" mode is

  present, and the number of illuminated diodes indicates the

calf of the holding force.

  A device is provided for detecting the state of the mandrel during the grinding and adjusting operations of the mandrel and thereby assuring the determination and control of the operation of the machine (Crectifieuse)

  to which the device is associated. For example, if a

  operating fault appears, for example an interruption

  If the current is flowing through the mandrel and the parts are not properly held on the mandrel, further grinding can dislodge the retained parts and cause injury or damage to the parts. The apparatus comprises a detection element of

  current intended to stop the operation of

  or to carry out otherwise a control operation.

  This detection component is indicated in its entirety by the reference 180 (FIG. 3, lower right portion) and comprises a detection resistor 182 of

  current and the voltage drop across this resistor

  This is applied to the inverting input pin n 2 of a comparator 184. A reference voltage is set at the comparator invert input pin 3 which

  is adjusted using a potentiometer 186. When the

  sion at pin n 2 is greater than that which is

  on pin 3, pin 6 out of the com

  parator goes to a low level. In "maximum" or "variable" mode, the output signal of the comparator (at pin n ° 6) is applied by the gates 188, 190 to the base of a transistor 192 which is then turned on and this transistor turns a opto-coupler 194 into a conductive state and this device in turn triggers the bidirectional controlled switch 196. This bidirectional switch in turn supplies a relay 198 which has contacts 198b and 198c (lower right portion of FIG. ). The relay 198, through these contacts, controls the operation of the grinding machine as indicated above, according to the state of the mandrel, that is to say as long as the mandrel is in proper order of operation, and keeps the parts in place, the grinder continues to work; however, in the event of a power interruption, an appropriate compensation step is then performed, for example the separation of the grinding wheel from the pieces, etc. The contacts 198b and 198c are normally open and normally closed contacts, respectively, conveniently, but other arrangements may be used instead.

where appropriate.

  The invention implements a new feature

  Stop tick to prevent the device from being accidentally set in an erroneous mode and the operator must follow the steps in a certain order. to continue the operation of the machine of the device. The stop mode can be implemented only after the device has

  has been set to "maximum" or "variable" mode. The characteristic

  stop tick can be used by incorporating a control or switching device into the device

  for this purpose, or it can be incorporated into the recti-

  to which the apparatus applies, but, in all cases, the stop control signals are applied to pins n 13, n 14, 200, 202 (lower right portion of Figure 7) respectively. The AC supply 30 (top of FIG. 3), for example at 115 V, transmits a current to these pads so that the transistor 204 (right of FIG. 7) is put in the conducting state and a negative voltage is applied to the inverting gate 206 and thus the pin n 10 of this gate passes to a high level. This sets transistor 208 to the nonconductive state and prevents the operation of all switches 62. The output signal of gate 206 transmitted by pin 10 is also applied to inverting gate 170 (top of FIG. 7). which in turn opens the digital switch 97 so that the potentiometer 64 (bottom of Figure 7) is turned off. The digital switch 167 (upper left part of Figure 5) is also open, by

  via the inverting gate 165 (upper part

  left of Figure 5). The opening of the digital switch 167 prevents the discharge of the capacitor 98

  so that the voltage at pin 5 of the cir-

  cooked pilot 78 is constant. The voltage of the pin 10 of the gate 206 (middle of FIG. 7) is also applied to the accumulation inlets ", i.e. to the pins # 5 of the pads 96", 96 "and 97" . The result is that the resistors which are switched on while the stop signal is applied, among the resistors 86, 88, 98 ',

  remain in circuit until the stop signal disappears.

  In fact, the continuous output signal remains at a certain

  pre-set level until the stop signal is

  premium. After removal of the stop signal, the output DC signal remains at the level at which the stop signal was applied, since the

  voltage at pin 5 of the pilot circuit 78 remains constant.

  aunt. This result is achieved because the digital switches 97 (top of Figure 7) and 167 (top of Figure 5) are still open. After removal of the shutdown feature, the only mode in which the device

  can be reset is the "release" mode.

Claims (8)

  1. Apparatus for demagnetizing a mandrel (20) having an associated electromagnet, and a circuit for connecting the mandrel to a source of electrical energy, a transformer device (50, 52) incorporated in the circuit and for providing a voltage, the circuit being for applying the voltage to the electromagnet, a first pilot circuit (78) of points and bars, which can be excited by the circuit, and a plurality of resistors (86, 88, 98 ' ) associated with the pilot circuit, and a device for adjusting the voltage applied to the pilot circuit and thus ensuring the connection of a corresponding number of resistors and consequently to apply a voltage corresponding to the mandrel, characterized in that it comprises a device (176, 178) for visually indicating the value   the tension thus applied to the mandrel.   2. Apparatus according to claim 1, characterized in that the visual indication device comprises a second pilot device (176) of points and bars connected in parallel with the first pilot device, and the apparatus comprises several lamps corresponding to the resistors and the second pilot device (176) illuminates the lamps in cooperation with the connection of the respective resistors. 3. Apparatus according to claim 2, characterized in that it comprises a device (52) for demagnetizing the mandrel during operation of which the first pilot device (78) selectively disconnects the resistors (86, 88, 98 ') and thus ensures the application of a voltage to the mandrel with decreasing steps, and that the second pilot device (176) individually turns off the lamps upon disconnection of the corresponding representative resistors (86, 88, 98 '). 4. Apparatus according to claim 1, characterized in that it can be set in each of several holding modes in which the holding powers are set to different values, and a holding mode in which no holding power n ' is applied, the circuit comprising switching devices (62A, 62B, 62C) for selectively placing the apparatus in these modes, the circuit comprising a stopping device   intended to inhibit the operation of mutation.   5. Apparatus according to claim 4, characterized in that the circuit comprises a device which, after the inhibition of the switching device, allows the   resetting the device only in a corresponding mode.   less than the maximum holding power. 6. Apparatus according to claim 1, characterized in that: the mandrel (20) is used in a grinding machine which is a machine tool, the circuit comprises a control device which is controlled by the excitation of the mandrel and which is intended to excite the grinding machine and which is sensitive to the detection of the excitation of the mandrel so that it prevents the operation of the grinding machine, the circuit is intended to ensure the excitation of the mandrel at different levels of excitation selectively, and the control device is intended to prevent the grinding machine from operating at any level excitation of the mandrel.   7. Apparatus according to claim 6, characterized in that the circuit comprises a comparator (184) and a detection resistor (182) connected across the mandrel and for controlling the comparator and thus   stop the operation of the grinding machine.   Apparatus according to claim 1, characterized in that the circuit includes a manually set switching device for selectively determining the value of the voltage applied to the driver circuit (76), and the driver circuit thus adjusts the number of resistances of output (86, 88, 98 ') which are in circuit and rule   thus the value of the tenation applied to the mandrel.