GB2271858A - Component locking in an electronic weighing machine - Google Patents

Description

2271858 COMPONENT LOCKING IN AN ELECTRONIC WEIGHING MACHINE The present

invention relates to a mainsoperated electronic weighing machine.

is Weighing machines of this kind with a motor-driven arresting device and/or motor-driven weight-switching device are generally known. To be understood by the term "weight-switching" is substitution weight switching, as used in analysis weighing machines, and calibration weight switching in which one or more calibrating weights can be lowered onto a measurement value pick-up. A weighing machine with calibration weight switching is described in, for example, DE-OS 38 15 626.

It is a disadvantage of the known machines that no arresting or change in the setting of the weight switching is possible on the failure of the mains voltage supply to the machine or on separation of the connection of the machine to the mains. Consequently, a manual actuation facility must be provided and/or a corresponding warning must be present in the operating instruction. However, these measures do not exclude the possibility that the operator of the weighing machine, when it is desired to transport the weighing machine to another place, simply pulls out the mains plug, lifts the machine up and transports it without attention to the manual facility or the warning. Thus, the weighing machine can be transported with sensitive components unlocked and/or in a setting of the weight switching device which is vulnerable to transport shocks.

There is thus a need for a weighing machine in which a movable component can be arrested automatically to allow transport without prior attention by the operator.

According to the present invention there is provided a mainsoperated electronic weighing machine comprising a load value detecting device, a electronic control, evaluating and display system for controlling the machine, evaluating detected load values and displaying weighing results, means drivable to produce an arrested state of a movable component of the machine, and a direct current electrical motor operable in response to a signal from the system indicative of interruption of mains voltage supply to the machine to drive said means to produce the arrested state, the system including, an electrical energy storage device arranged to supply sufficient energy to the motor, after interruption of the mains supply, to enable operation of the motor until the arrested state is produced.

In one preferred embodiment, in which the weighing machine has an arresting device, the arresting device is driven by the direct current electrical motor and the electronic system on interruption of the mains supply voltage gives to the motor a command for arresting, the motor being associated with a capacitor with a capacitance so dimensioned that it can, without further energy feed, supply the motor with energy up to the end of the arresting operation. In another embodiment, in which the weighing machine has a weight-switching device, this is achieved ipthat,, the weightswitching device is driven by the direct current electrical motor and is the electronic system on interruption of the mains supply voltage gives to the weight-switching motor a command to move the weightswitching device into the arresting position, the motor being associated with a capacitor with a capacitance so dimensioned that it can, without further energy feed, supply the motor with energy until the arresting position is reached.

If the weighing machine comprises both a motor-driven arresting device and a motor-driven weight-switching device, both features can function separately from each other, thus with separate motors, but a common motor can be used.

In order, in the case of for example only brief voltage supply to the machine, to prevent the movable component having to remain in an unarrested state, for preference the motor or motors for the unarresting and/or for the resetting of the weight-switching device is or are released from the arresting position only after the capacitor has been charged up to a sufficient level. This can be effected by, for example, an appropriately dimensioned time delay element or an appropriately arranged electronic monitor.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic sectional view of an upper pan weighing machine, with weight-switching device, embodying the invention; Fig. 2 is a circuit diagram of a control circuit of the machine; Fig. 3 is a schematic sectional view of an analysis weighing machine or microbalance, with an arresting device.,embodying the invention; and Fig. 4 is a schematic sectional view of an analysis weighing machine or microbalance, with a weightswitching device, embodying the invention.

Referring now to the drawings, there is shown in Fig.1 an electronic weighing machine comprising a system carrier 1, which is fixed relative to a housing of the machine and at which a load receiver 2 is fastened to be movable in vertical direction by way of two guide rods 4 and 5 with hinges 6. The load receiver 2 in its upper part carries a load pan 3 for reception of a load to be weighed and transmits the force corresponding to the mass of the load by way of a coupling element 9 to a load arm of a transmission 1 ever 7. The lever 7 is mounted on the carrier 1 by a crossspring joint 8. A coil body with a coil 11 is secured to a compensating arm of the lever 7. The coil 11 is disposed in an air gap of a permanent magnet system 10 and produces a compensating force. The magnitude of the compensating current through the coil is regulated by a position sensor 16 and a regulating amplifier 14 so that equilibrium prevails between the weight of the load and the electromagnetically produced compensating force. The compensating current produces a measurement voltage which is fed across a measuring resistor 15 to an anal og-to-digital converter 17. The digitalised result is taken over by a digital signal-processing unit 18 and indicated digitally in a display 19. Also present is a T temperature sensor 26, which transduces the temperature of the measurement value pick-up into a digital signal and feeds it by way of a line 31 to the unit 18. The unit 18 can thereby correct temperature- induced errors in the measurement value.

The load arm of the transmission lever 7 has a prolongation 12 extending beyond the fastening point of the coupling element 9 and continuing as a downwardly offset part 22. Fastened at the part 22 are three vertical centring pins, of which only two pins 24 and 25 are visible in Fig. 1. These centring pins carry a calibrating weight 13. The weight has a bore 29, which extends frombelow and terminates in a conical surface 23. The bore passes exactly through the centre of gravity of the weight 13 so that the conical surface lies vertically above that centre of gravity.

Also shown in Fig. 1 is a lifting device for the calibrating weight 13, the device comprising a prong 20 guided in a sleeve 21, which is fixed to the housing, to be movable in vertical direction. The device for the movement of the prong is indicated schematically by an eccentric 28 and a direct current electrical motor 41. The prong 20 extends through an opening 27 in the part 22 and into the bore 29 in the calibrating weight 13. In the illustrated setting, in which the weight rests on the centring pins and thereby on the transmission lever, the conical tip of the prong is disposed closely below the conical surface 23. When the prong is raised by the eccentric 28, it comes into contact with the conical surface 23. lifts the weight 13 off the transmission lever and urges it against abutments 39 fixed to the housing. This is the normal setting of the calibrating weight (weighing position and arresting position), whereas the lowered setting shown in Fig. 1 is assumed only for a calibrating process. The centre of gravity of the weight 13 can be displaced slightly by the screw 38 so that a fine adjustment can be achieved.

After actuation of a calibrating key (not shown), the digital signal processing unit 18 activates a calibration control 40 by way of a 1 i ne 36. The control 40 starts the motor 41 and, after the calibrating weight 13 has been placed on the transmission lever 7/12/22, the unit 18 waits for the measurement value from the pickup to settle down, takes over the value, computes and stores a new calibration factor and,by way of the control 40, causes the motor to lift the weight 13 back into the weighing/arresting position.

The parts of the weighing machine described so far are generally known and therefore have been described only briefly in terms of function and construction.

The calibration control 40 includes a capacitor 30 as an energy storage device. This capacitor 30 is always kept charged. As long as mains supply voltage is applied without interruption, the capacitor does not come into function. Only when the mains supply voltage for the weighing machine is interrupted, for example, when the mains plug is pulled out of the supply socket, and when the calibrating weight-switching device is disposed in the calibrating state or a transitional state at that instant, does the capacitor 30 become effective to supply energy to drive the motor 41 to cause the weighing and arresting position to be restored. The control 40 receives the command for this operation from a voltagemonitoring circuit within the microprocessor 18 or from a separate voltagemonitoring circuit.

An exemplary circuit for the control 40 of the motor 41 is illustrated in Fig. 2. The capacitor 30, which can have, for example, a capacitance of 1 farad, is charged by a diode D1, wherein the internal resistance of the supply voltage limits the charging current. When the voltage at the capacitor 30 reaches the threshold voltage of a Zener diode PD.3, T, a transistor T1 becomes conductive and one input 50 of a gate IC1.1 is set to high level. The microprocessor 18 can then, by way of the line 36 and a transistor T5, switch the gate 1C1.1 to be conductive and control the drive of the direct current motor 41 by way of a diode D2, resistors R4 and R6 and a transistor T2. A resistor RS in that case serves for current limitation for the motor 41. The circuit part 55 framed by dashed lines also functions as a monitoring circuit which permits the microprocessor 18 to control the drive of the motor 41 only after a minimum voltage across the capacitor 30 has been reached. It is thereby achieved that, after the switching-on of the supply voltage, the motor 41 can operate only after the energy stored in the capacitor 30 is sufficient to let the motor 41 run back again into its initial setting.

The motor 41 now causes the calibrating weight 13 to be lowered onto the lever 7/12122 for calibration, as described by reference to Fig. 1. The reaching of the calibrating position is reported to the microprocessor 18 by way of a line 51 through opening of a switch S2. The microprocessor 18 thereupon stops the motor 41 by way of the line 36. A transistor T3 in that case acts as short- circuit brake. Brief running-on of the motor 41 does not cause difficulties in that case, since the prong 20 rests on the flat minimum of the eccentric 28 and its tip has a spacing from the surf ace 23. After standstill of the weighing machine and takeover of the calibrating result into the microprocessor, the microprocessor 18 starts the motor 41 again and the motor runs until reaching the weighing/arresting position, which is reported to the microprocessor by way of a line 52 through the opening of a switch S1. The microprocessor then stops the motor 41.

If the mains supply voltage is now interrupted, an input 53 of a gate IC1. 4 falls to low level. If the switch S1 is open, i.e. the calibrating weight-switching device is in the weighing state,Which is equal to the arresting position, then nothing happens. if, however, the switch S1 is closed, thus if the motor 41 is running or if the device is in the calibrating state, then also an input 54 of a gate IC1.3 is at low level and a gate IC1.2 switches through and supplies or continues to supply the motor 41 with current by way of a diode D3, the resistors R4, R6 and the transistor T2. The motor 41 thus continues to run, or starts up and runs, and stops only when the switch S1 opens. The gates IC1.1 to IC1.4 receive their operating voltage Vo directly from the capacitor 30 and are types which also operate with low operating voltage, so that, even if the capacitor 30 is discharging, their function is ensured until the end position of the motor 41 is reached.

If the weighing machine is not controlled by a microprocessor, the drive control of the motor 41 can, of course, be realised by other circuits. For example, these can include relays which are so connected that when all relays drop back into the rest position, the motor 41 receives current from the capacitor 30 until the weighing and arresting position is reached.

A second embodiment of electronic weighing machine is shown in Fig. 3, in particular a lower pan analysis weighing machine or microbalance with motor-driven arresting. The weighing machine comprises a housing 61, which encloses a weighing chamber 62, a chamber 63 for a measurement value pick-up and a chamber for the electronic system 64. The pick-up again operates on the principle of electromagnetic force compensation and consists of a beam 65, which is mounted to be rotatable by means of a spring joint 67 on a block 66 fixed to the housing. Depending from a shorter lever arm of the beam 65 is a movable intermediate member 60, which in the lower region 68 carries a weighing pan stirrup69 and a weighing pan 70. Fastened to a longer lever arm of the beam 65 is a coil 71, which is disposed in the field of a permament magnet system 72.

A] so present is an electronic system 64, of which only a drive control circuit 73 for arresting and an associated capacitor 74 are indicated. Arranged at the front of the machine is a display 75 for the weighing result.

is To enable safe transport, the weighing machine of Fig. 3 has an arresting device which consists of two levers 76 and 77 for locking the beam 65 and two pressure chambers 78 and 79 for locking the movable intermediate member 60. The arresting levers 76 and 77 are mounted at their righthand ends at fixed points 80 and 81 of the housing 61 and, for locking, are acted on near their other ends by eccentrics 82 and 83 and urged against the beam 65 to arrest it. The eccentrics are driven by a direct current electrical motor (not shown) and controlled selectably by the drive control circuit 73. This drive control circuit 73 functions as already described in rel at i on to Figs. 1 and 2 and drives the arresting device automatically in the event of the mains supply voltage to the weighing machine being interrupted. In the same manner, the movable intermediate member 60 is locked for transport by means of the pressure members 78 and 79, the associated eccentrics 84 and 85 and a further direct current electrical motor (not shown).

A third embodiment of the electronic weighing machine, with a substitution weightswitching device, is shown in Fig. 4. Parts corresponding to those in Fig. 3 are denoted by the same reference numerals and are not further explained. The substitution weight switching device consists of a weight carrier 90, which is secured to the movable intermediate member 91 and carries several weights 92, of which only two are illustrated, by way of example, in Fig. 4. The weights 92 can be lifted off the carrier 90 by hooks 93, which are attached to the housing at points 94, and can be arrested in this raised position. The transport position is that position in which all weights are lifted off. In Fig. 4, all weights are shown lowered and resting on the carrier 90, which is the zero setting. The hooks 93 are moved by eccentrics 95, which in turn are driven by direct current electrical motors (not illustrated). The control of the motors is effected by an electronic drive control system 96 which, according to the load on the weighing pan 70, lays more or fewer weights 92 onto the carrier 90 or removes them therefrom until there is approximate equilibrium at the beam 65 and the remaining weight difference can be compensated for by the coil of the electromagnetic force compensation system. On interruption of the main supply voltage, the electronic system 96 controls the direct current electrical motors so that the weights are all lifted off, which represents the transport position, and draws the energy necessary for this from the capacitor 74.

The mechanical parts are illustrated only schematically in the drawings, as the exact construction is not relevant to the actual invention. Specific constructions can be readily determined by the expert.

In a weighing machine with both an arresting device and a weightswitching device, separate direct current electrical motors can, of course, be provided for the arresting device and for the weight-switching device. In that case, a separate capacitor for energy storage can be provided for each motor or both motors can be supplied with energy from a single capacitor. It is also possible to use a single direct current electrical motor for both functions and, by means of additional couplings, drive either the arresting device or the weight-switching device or both.

Claims (12)

1. A mains-operated electronic weighing machine comprising a load value detecting device, an electronic control, evaluating and display system for controlling the machine, evaluating detected lead values and displaying weighing results, means drivable to produce an arrested state of a movable component of the machine, and a direct current electrical motor operable in response to a signal from the system indicative of interruption of mains voltage supply to the machine to drive said mens to produce the arrested state, the system including an energy storage device arranged to supply sufficient energy to the motor, after interruption of the mains supply, to enable operation of the motor until the arrested state is produced.
2. 2. A weighing machine as claimed in claim 1, the movable component being a part of the detecting device and said means being an arresting device for arresting the part.
3. 3. A weighing machine as claimed in claim 1, the movable component being a load to load the detecting device and said means being a displacing device to displace the load into and out of an arrested position.
4. 4. A weighing machine as claimed in claim 1, comprising further such means drivable to produce an arrested state of a further movable component of the machine, the motor being operable to drive both said means.
5. 5. A weighing machine as claimed in claim 1, comprising further such means drivable to produce an arrested state of a further movable component of the machine, and a further such motor operable to drive the further means, the storage device being arranged to supply such energy to both motors.
6. 6. A weighing machine as claimed in claim 1, comprising further such means drivable to produce an arrested state of a further movable component of the machine, a further such motor operable to drive the further means., and a respective such storage device to supply enery to each motor.
7. 7. A weighing machine as claimed in any one of claims 4 to 6, the two movable components being a part of the detecting device and a load to load the detecting device and the two said means being an arresting device for arresting the part and a displacing device to displace the load into and out of an arrested position.
8. 8. A weighing machine as claimed in any one of the preceding claims, wherein the storage device comprises a capacitor.
9. 9. A weighing machine as claimed in any one of the preceding claims, wherein the system includes a monitor to monitor the energy being stored by the storage device following application of mains voltage to the machine and to permit operation of the motor or motors, as the case may be, by the mains voltage only after the stored energy is sufficient for the arrested state to be produced through operation of the motor or motors solely by supply of that energy.
10. 10. A weighing machine as claimed in any one of the preceding claims, wherein the system includes a time delay element effective, following application of mains voltage to the machine, to permit operation of the motor or motors, as the case may be, by the mains voltage only after a predetermined time period.
11. 11. A weighing machine substantially as hereinbefore described with reference to any one of Figs. 1, 3 and 4 of the accompanying drawings.
12. 12. A weighing machine as claimed in claim 10 and substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

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