GB2281826A

GB2281826A - Preventing excessive motor speed

Info

Publication number: GB2281826A
Application number: GB9416483A
Authority: GB
Inventors: Guenther Boesche; Rupert Weber; Olaf Kunz; Gerhard Froehlich; Alfred Punzert
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-09-13
Filing date: 1994-08-16
Publication date: 1995-03-15
Anticipated expiration: 2014-08-16
Also published as: DE4330823A1; GB2281826B; ITMI941854A1; CH689133A5; ITMI941854A0; DE4330823C2; IT1275023B; GB9416483D0

Description

1 2281826 Drive device with a safety device for special-OReration

The prior art

The invention proceeds from a drive device according to the type of the main claim. Drive devices of this kind are commonly known. They are used widely inter alia in machine tools and robots where they are used to drive movable elements. With machines and robots alike there is an operating danger for the operator from the movements of moveable elements during normal operation. For accident prevention, plants of this kind therefore as a rule comprise a safety device which only permits operation of the moveable elements when it is ensured that no operator is within the machine or robot radius of action. This is effected in a simple manner, for example, by covers or doors which must be closed as a prerequisite for normal operation. Situations regularly arise however in which an operator has to enter the radius of action of the machine or robot, for example to change tools, to set a machine or to programme a robot. So that this may be possible, a part of the safety conditions which are to be complied with during normal operation, is annulled. In order also to guarantee sufficient operational safety in this form of operation, referred to hereinafter as special operation, the VDI standard 2854 for example requires that the rate of motion for all movable axes is limited to a maximum value of 2 m/minute. The regulation of the standard furthermore demands that the recording of the speed for each axis is effected abundantly, i.e. at least twice. A simple way of satisfying the last requirement in 2 particular, is to arrange two revolution counters at the motor or the moved part, one normally being available anyway to monitor the signals of the two sensors when a maximum value is exceeded. By arranging a further revolution sensor at the motor, the constructional size of the motor is possibly considerably enlarged, particularly with small motors. Additionally. for the same reason, the drive increases in price.

The object of the present invention is therefore to specify a drive device with an electronically commutated motor which guarantees high safety for an operator also during special operation, without substantial additional expenditure with regard to design and the costs associated therewith.

This object is achieved by a drive with the characterizing features of the main claim.

A drive device according to the invention requires only one, already available revolution sensor. A further revolution signal for safeguarding abundant recording is obtained by utilizing at least one motor phase current. The concept is achievable with small additional expenditure. As a rule, only one additional current sensor is required in the motor supply lines. It has the additional advantage of retrofitting onto available plants. It also readily complies with the accident prevention regulations laid down, for example, in the VDI standard 2854.

The detection of the second revolution signal expediently takes place in a central control unit which also controls the motor. The signal recorded by the current sensor is expediently digitized for this.

According to a further expedient accomplishment for obtaining a second revolution value, the fundamental wave is filtered out of the signal supplied by the current sensor by means of an analog filter in order to derive revolution information from the fundamental wave.

It is particularly advantageous, in addition to the number of revolutions themselves, to monitor at least one of the internal signals in the motor regulator which controls the dynamic behaviour of the drive. In so doing, it can be advantageously recognized in advance whether an axis rate of motion will exceed a specified limit value. Such monitoring also offers the advantage of retrofitting onto available drives. Moreover, it can advantageously be included into the machine or robot monitoring during normal operation.

An embodiment of the invention is explained in more detail in the following with reference to the description.

Drawing The Figure shows a block switch diagram of a proposed drive device.

Description

The main components of the drive shown in Figure 1 are a mains rectifier 11 for supplying a constant-voltage intermediate circuit 12, an inverse rectifier 13 connected to the circuit 12 and a motor 14 supplied by the inverse rectifier. Between the mains rectifier 11 and the A.C. network 24, a contactor or a comparable electromagnetic power switch 16 is connected. on at least one of the phase supply lines 17 to the motor 14, a sensor 18 for recording the phase current supplied to the motor 14 is located. Connected directly to the motor 14, a revolution sensor 15 is disposed. Substantial components of the mains rectifier 11 and the inverse rectifier 13 are in each case power semiconductors. They are controlled by a control 10 which also controls the power switch 16. For this purpose, the 4 control is connected bidirectionally to the elements of the mains rectifier 11, inverse rectifier 13 and power switch 16. The signal of the revolution sensor 15 and the current signal recorded by the sensor 18, 18F, are led to the control, as a rule, by means of unidirectional connections.

The main components of the control 10 - the structure shown was chosen for explaining the invention described here, it is not mandatory and can differ in practice from the one illustrated - are a central control unit 20 which above all controls the motor 14, that means the regulating of the number of revolutions n, rotor position L and current I, a store 23, a user specific integrated switching circuit 19 (ASIC) which evaluates the signals of the normally highresolution revolution sensor 15 and makes available information iherefrom, to the central control unit 20, about the rotor position L and the number of revolutions n of the drive 14 in the form of binary data. The control also comprises an input/output componentry 22. The central control unit 20 and the switching circuit 19 further form the main components of a safety device, the function of which is explained in the following. All named elements are connected by means of a data bus 24. An analog/digital converter 21 connected in series to the central control unit 20 is further used for digitizing the readings coming from the sensor 18, 181.

The arrangement shown has the following functions. If the drive 14 is in the special mode of operation, then the control 10 monitors the element moved by the drive 14, whilst maintaining a specified maximum value rate of motion. The maximum value is expediently held in a special area of the store 23 as a revolution signal, said signal being proportional to the rate of motion of the moved element. The monitoring is effected twice. On the one hand the control 10 monitors the revolution signal n supplied by the revolution sensor 15 when the specified limiting value is exceeded. This takes place expediently with the aid of the user specific integrated switching circuit (ASIC) 19, to which the reading of the revolution counter 15 is directly led. The switching circuit 19 works independently of the processor of the central control unit 20 with regard to this revolution monitoring. The control 10 detects a second revolution value from the measuring signal of the phase current to the motor 14, supplied by the sensor 18, 181. As a rule this current has a sinusoidal course, the frequency of the sinusoidal oscillation being proportional to the number of revolutions. The detection of the second revolution value from the phase current can, as shown in the Figure, take place in the central control unit 20 after firstly converting the analog measuring signal into a digital value I. Another possible embodiment is to provide a filter circuit known per se, which firstly detects a likewise analog revolution signal from the analog readings of the sensor 18. In a simple manner, such a filter circuit is a low-pass filter, the cut-off frequency of which is such that the filter filters out the fundamental wave of the motor current. A comparator circuit connected after the filter supplies a signal proportional to the number of revolutions by detecting the zero crossing of the fundamental wave. This signal in turn is expediently converted into a digital value, for example by the analog/digital converter 21. To support the significance of the signal obtained with the low-pass filter, the cut-off frequency is always expediently tracked correspondingly to the respective desired revolution value. The second revolution signal obtained is likewise compared by the control unit 20 with the maximum value held in the store 23. Should either the central control unit 20 or the user specific integrated switching circuit 19 ascertain that one of the revolution signals exceeds the maximum value held in the store 23, then the ascertaining unit sends a signal to the input and output componentry 22 which leads to the shut down of the drive. The said unit causes the shut down 6 through simultaneous clearing of the power switch 16 from the A.C. network 24 and the disconnecting of the inverse rectifier 13. The double interruption in turn ensures redundancy; Should either the clearing of the power switch 16 from the A.C. network 24, or the disconnecting of the inverse rectifier 13 fail, the motor 14 is nevertheless shut down. The above described revolution monitoring is not limited to use during special operation. With a correspondingly adapted revolution maximum value it can of course likewise be used in normal operation.

Additionally or alternatively to the number of revolutions, the control 10 monitors certain internal control signals arising when the specified range of values in the control circuits for controlling the current I, number of revolutions n, and position L of the motor 14, is exceeded. These signals correspond to a perfect operation of the drive by maintaining the specified limiting speed during special operation. They are expediently held in a special area of the store 23. The motor regulator normally has a cascade structure, the number of revolutions regulator being connected in series to the current regulator, the positioning regulator in turn being connected in series to the number of revolutions regulator. A suitable internal control signal for monitoring, for example, is in this case the output signal of the positioning regulator, which signal shows the desired value for the number of revolutions regulator connected after it. A further suitable signal is formed by the way in which the number of revolutions regulator is set, which, with corresponding variations, exceeds regulator limiting values specifiable between the desired and actual number of revolutions. When the specified internal limiting values are exceeded, the control 10 locks into excess of the specified limiting speed or an interference of the drive. In this event, the control in turn conveys a signal to the input and output unit 22, which leads to the shut down of the power switch 16 and inverse 7 rectifier 13. An advantage of monitoring the internal control signals as opposed to the simple monitoring of the measured actual number of rotations, is that excesses of the specified axis limiting speed or faults in the drive can be recognized, in many cases, before the excess or the fault in the motor 14 actually takes place.. The monitoring of the internal control signals is not only sensible during special operation but also during normal operation. It can be brought into play in particular here for the early recognition of faults in the drive.

Whilst keeping to the basic concept, by using as many as possible of the already available signals to abundantly monitor a drive whilst maintaining a specified number of revolutions, diverse variations of the arrangement shown in Figure 1 are possible. This applies in particular to the design and structure of the-control 10.

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Claims

1. Drive device with an electronically commutated motor, a constantvoltage intermediate circuit, an inverse rectifier connected to the circuit for controlling the motor and a safety device which monitors the number of revolutions of the motor whilst maintaining a specifiable maximum value during special operation and which interrupts the energy supply to the motor when a revolution signal is larger than the specified maximum value, the revolution signal being formed by recording the signal supplied by a revolution sensor, characterized in that the safety device derives a further revolution signal from the temporal course of the current in at least one of the phase supply lines (17) to the motor (14) which current it detects by means of a sensor (18, 180').

2. Drive device according to claim 1, characterized in that the safety device comprises a central control unit (20), which processes digital signals, for determining the further revolution signal, to which control unit the readings of the current sensor (18, 18f) digitized in an A/D converter (21), can be guided.

3. Drive device according to claim 1, characterized in that the determining of the further, in particular of the second revolution signal is carried out by analog filtering of the fundamental wave of the temporal course of the motor current recorded by the current sensor (18, 18f).

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4. Drive device according to claim 1, characterized in that the interruption of the energy supply to the motor (14) is carried out by switching an electromagnetic power switch (16) connected in series to the mains rectifier (11) and/or by disconnecting the inverse rectifier (13).

5. Drive device according to claim 2, characterized in that the comparison of the revolution signal (n) obtained by an electromechanic revolution sensor (15), with the specified maximum value, is carried out in a switching circuit (19) independent of the central control unit (20).

6. Drive device according to claim 1, characterized in that the control of the motor (14) at least includes the control of current and number of revolutions and that the safety device records at least one internal control signal arising during the controlling, then tests whether the signal lies within a specified range of values and interrupts the energy supply if it lies outside the specified range of values.

7. Drive device according to claim 6, characterized in that the motor control has a cascade structure, a number of revolutions regulator being connected in series to a current regulator and a positioning regulator being connected in series to the number of revolutions regulator and that the internal control signal is the output signal of the positioning regulator.

8. Either of the drive devices substantially as herein described with reference to the accompanying drawing.