Control and monitoring arrangements for an aperture closure member

Current through a motor is sensed to create a voltage which is amplified. The amplifier is followed by a high pass filter and a low pass filter. This recovers commutator pulses from the motor current, rejecting mains ripple and higher frequency noise. Commutator pulses are counted. Other arrangements could be used for injecting pulses into the motor supply, for counting at a remote position. Various techniques are described for controlling the motor in accordance with the result of counting.

This is a national stage application filed under 35 USC 371 based on International Application No. PCT/GB2004/001216 filed Mar. 19, 2004, and claims priority under 35 USC 119 of United Kingdom Patent Application No. 0306390.6 filed Mar. 20, 2003.

The present invention relates to control and monitoring arrangements.

DC motors are commonly used to drive items such as aperture closure members. It may be necessary to control and monitor the position of the aperture closure member for safety or other reasons. For example, when the aperture closure member is a sliding door, roller shutter door or the like, it may be necessary to monitor the member while it is closing, in order to detect the presence of an obstruction, and take appropriate remedial action, such as stopping or reopening the door.

The present invention provides a DC motor current monitoring arrangement, comprising:

current sensing means operable to create a waveform signal representing the waveform of the motor current;

filter means for the waveform signal and providing a high pass filter function and a low pass filter function, the high pass function having a frequency threshold above the frequency of mains interference and below the frequency of pulses in the waveform signal and indicative of movement created by the motor, and the low pass function having a frequency threshold above the frequency of the said pulses,

whereby the pulses are passed by the filter means to be available for counting.

The pulses may be commutator pulses. The pulses may be injected into the motor current in dependence on the said movement.

The filter means may comprise separate high pass and low pass filter means. The low pass filter means preferably follows the high pass filter means.

The arrangement may further comprise amplifier means. The amplifier means is preferably operable to amplify the waveform signal prior to filtering by the filter means.

The frequency threshold of the low pass filter function is preferably above the highest frequency of pulses to be created by the motor.

The arrangement may further comprise counter means operable to count pulses passed by the filter means. The counter means may be provided by a processor device.

The invention also provides a method of monitoring DC motor current, in which a waveform signal representing the waveform of the motor current is created and is filtered by a high pass filter function and a low pass filter function, the high pass function having a frequency threshold above the frequency of mains interference and below the frequency of pulses in the waveform signal and indicative of movement caused by the motor, and the low pass function having a frequency threshold above the frequency of the said pulses, whereby the pulses are passed by the filter means to be available for counting.

The pulses may be commutator pulses. The pulses may be injected into the motor current in dependence on the said movement.

The high pass and low pass filter functions may be applied separately, preferably with the low pass filter function following the high pass filter function.

Amplification may be applied, preferably to amplify the waveform signal prior to filtering.

The frequency threshold of the low pass function is preferably above the highest frequency of pulses in the DC motor current.

Pulses passed by the filter functions are preferably counted, such as by means of a processor device.

In a second aspect, the invention provides a monitoring arrangement for use with a DC motor, the arrangement comprising:

detecting means for detecting movement of an item driven by the motor, to produce a pulse train; and

switch means operable to change state to cause current to be drawn from or to cease to be drawn from the motor supply, the state of the switch means being controlled by the pulse train in order to inject a pulse train into the motor supply.

The detecting means preferably comprises a sensor responsive to one or more features of the item to detect movement thereof. The detecting means may comprise a Hall Effect sensor responsive to the movement of one or more magnets carried by the item. The item may be rotatable, to cause the or each feature to repeatedly pass the sensor. The detecting means may further comprise an oscillator operable to provide an oscillating output only when enabled by the sensor. The sensor may enable the oscillator when passing of the feature is detected.

The arrangement may include a second monitoring arrangement remote from the first monitoring arrangement and operable to detect a pulse train carried on the motor supply, whereby communication between the monitoring arrangements may be solely by means of the motor supply. The second monitoring arrangement may be a monitoring arrangement in accordance with the first aspect of the invention.

In a third aspect, the invention provides an aperture closure member control arrangement, comprising:

pulse means operable to create a train of pulses as the closure member moves;

counter means operable to count pulses of the train;

control means operable to determine the position of the closure member from the pulse count and to provide an output for modifying the manner in which the closure member is driven, in accordance with the predetermined position;

wherein the control means determines at least one speed change position and a reversing position and causes, in use, the speed of the closure member to change as the closure member passes the speed change position in at least one direction, and causes, in use, the response to an obstruction to change as the closure member passes the reversing position in at least one direction.

The pulse train may be created by a sensor responsive to one or more features of an item driven by a drive means which drives the closure member. The pulse train may be created by commutation of a DC motor used to drive the closure member.

The counter means preferably counts pulses created by different means at different positions of the closure member. The choice of pulses to be counted is preferably changed as the closure member passes the speed change position.

Preferably the pulses are provided to the counter means by an arrangement in accordance with the first or second aspect of the invention.

Preferably a speed change position is located near a fully open or fully closed position of the closure member, and the closure member is caused, in use, to slow down as the closure member passes the speed change position in the direction of the fully open or fully closed position. Speed change positions may be located near a fully open and near a fully closed position.

The reversing position is preferably located near the fully closed position of the closure member, and the closure member is caused, in use, to re-open when obstructed while closing, unless the closure member is between the reversing position and the fully closed position. The closure member may be caused, in use, to stop when obstructed while closing, if the closure member is between the reversing position and the fully closed position.

The reversing position is preferably between the fully closed position and the or the corresponding speed change position.

The invention also provides a method of controlling an aperture closure member, in which a train of pulses is created as the closure member moves, pulses of the train are counted and the pulse count is used to determine the position of the closure member and to modify the manner in which the closure member is driven, in accordance with the determined position, wherein at least one speed change position and a reversing position are defined, and the speed of the closure member changes as the closure member passes the speed change position in at least one direction, and the response to an obstruction changes as the closure member passes the reversing position in at least one direction.

The pulse train may be created by a sensor responsive to one or more features of an item driven by a drive means which drives the closure member. The pulse train may be created by commutation of a DC motor used to drive the closure member. The pulse count may be derived from pulses created by different means at different positions of the closure member. Preferably the choice of pulses to be counted is changed as the closure member passes the speed change position.

Preferably the train of pulses is created in accordance with the method of the first aspect of the invention.

Preferably the closure member is slowed down as the closure member passes the speed change position in the direction of the fully open or fully closed position. There may be speed change positions located near a fully open and near a fully closed position.

The closure member is preferably caused to re-open when obstructed while closing, unless the closure member is between the reversing position and the fully closed position. The closure member is preferably caused to stop when obstructed while closing, when the closure member is between the reversing position and the fully closed position.

Preferably the reversing position is between the fully closed position and the or the corresponding speed change position.

FIG. 1illustrates an aperture closure member arrangement10. A closure member in the form of a door12formed of articulated slats12A is guided along a track14, which has a generally vertical leg14A and a generally horizontal leg14B. Drive to the door12is provided by a shaft16which in turn is driven by a DC electric motor18through two pulley wheels18A connected by a drive belt18B, as shown schematically inFIG. 1A.

A similar track (not shown) is provided at the other side of the door12. The tracks are installed with the vertical legs extending up either side of the aperture to be closed (such as an aperture in the outer wall of a building). The horizontal legs of the tracks extend back from the aperture, into the building. When the door12is closed, the slats12A form a vertical barrier between the vertical legs of the tracks. To open the door, operation of the motor18and shaft16moves the door up to a horizontal position, supported by the horizontal legs of the tracks. The motor has a fast speed and a slow speed, the latter being used when the door is approaching the ends of its range of movement.

The motor18is shown schematically inFIG. 2, which also shows a monitoring arrangement for monitoring the current supply to the motor18.

The motor18is connected through relays20A,20B between a positive supply rail22and ground potential at24. The relays20A,20B are shown in their de-energised condition. The motor18is disconnected from the rail22and inoperative. Energising one of the relays20A,20B will cause the corresponding side of the motor18to be connected to the rail22, allowing DC current to pass through the motor18, turning the motor. This, in turn, turns the shaft16and drives the door12. The direction of the motor18, and thus the direction of movement of the door12is determined by the choice of relay20A,20B, so that the motor18can be driven in either direction, according to this choice.

The motor18is a DC motor which may be conventional in itself. The motor18will have a commutator arrangement by means of which the current is switched between the coils of the motor, as the motor turns.

Motor current is sensed at26by means of a motor current sense resistor28. This is in series with the motor18to create a voltage at26which varies as the motor current varies.FIG. 4illustrates a typical voltage at26, and will be described in more detail below.

The voltage from point26is applied to an amplifier30by means of a series capacitor C1and resistor R1connected to the non-inverting input32of the amplifier30. Within the amplifier30, a feedback arrangement is provided by resistors R2, R3to provide an overall gain set by the ratio R2/R3.

The input32is biased by means of three resistors R4and an associated capacitor C2to provide an intermediate rail34at a voltage intermediate the voltage of the main supply rail36for the current monitoring arrangements27.

The output of the amplifier30is applied to a high pass filter38which is of conventional design, based around an operational amplifier40. Input from the amplifier30is applied to the non-inverting input of the amplifier40through series capacitors C3, C4. Feedback is applied at42through a resistor R5. Bias is applied to the non-inverting input by resistor R6connecting that input to the intermediate rail34.

Feedback to the inverting input40B is provided from the common terminal of a voltage divider formed by series resistors R7connected between the output of the filter38, and the intermediate rail34.

The output44of the high pass filter38is applied as the input of a low pass filter46, based around a further operational amplifier48. The low pass filter46is again conventional in itself, having series resistors R8connected from the output44to the non-inverting input48A, and feedback through a capacitor C4to the point50between the resistors R8. The non-inverting input48A is coupled to the intermediate rail34by a capacitor C5.

A voltage divider provided by resistors R9is associated with the output52of the filter46, the inverting input48B and the intermediate rail34, in a similar manner as the connections of the resistors R7within the high pass filter38.

The output52is connected through a series protection resistor R10to an analogue input of a microcontroller54. The microcontroller54is controlled by appropriate software. Within the microcontroller54, an analogue-to-digital converter is provided at56to convert the waveform received from the filter46to a pulse train, which is counted by an up/down counter58. The counter58is controlled to increment or decrement by an input60from an operator control (not shown). The input60indicates the required direction of movement. The input at60is also passed on, at60A, to control the operation of selecting one of the relays20A,20B in order to determine the motor drive direction.

A further circuit, shown inFIG. 3, is associated with the motor18and will be described more fully below. The purpose of the circuit ofFIG. 3is to inject additional pulses into the current sensed by the resistor28, for reasons which will also be described below. In order to obtain a clearer understanding of the invention, it is first appropriate to describe operation of the current monitor arrangement27in more detail, with reference toFIGS. 4 to 6, and in the absence of operation of the circuit ofFIG. 3.FIGS. 4 to 6show waveforms at various positions through the arrangement27.

FIG. 4illustrates an example of the voltage expected at26, arising solely from the current through the motor18. This exhibits an approximate sinusoidal form arising from the presence of relatively low frequency mains supply ripple. In the U.K., mains supply ripple will be at a frequency of 100 Hz. Pulses in motor drive current, caused each time the commutator switches, are also present. InFIG. 4, the commutator pulses64are illustrated at a frequency of about 1 kHz, which may correspond with fast operation of the motor18. In slow operation mode, the commutator pulses may be at 400 Hz. Other frequencies for fast and slow operation may be chosen, particularly in the light of factors such as door weight etc.

The waveform is also found to exhibit short pulses of very high frequency noise66, arising from commutator contacts arcing, bouncing or the like.

The waveform ofFIG. 4is first applied to the amplifier30. The gain of this amplifier is set so that the final output at52swings across substantially the whole of the voltage range acceptable at the microcontroller54in order to provide good discrimination between cycles of the waveform, to improve the quality of the pulse train created by the A/D converter56. The bias of the amplifier30causes the output52to be centred at the voltage of the intermediate rail34.

The amplified waveform is applied to the high pass filter function provided at38. The frequency threshold of the high pass filter function is chosen to be above the frequency of the mains supply ripple, but below the frequency of the commutator pulses64. In this example, the frequency threshold would be between 100 Hz and 400 Hz. It will be understood by the skilled reader that a precise cut-off frequency will not be provided by a filter of the design shown inFIG. 2, but that the components can readily be selected in order to cause the filter38to reject mains supply ripple, resulting in an output at44as shown inFIG. 5, containing only the commutator pulses64and the noise66. Mains supply ripple62has been removed.

The waveform ofFIG. 5is then applied to the low pass filter function provided at46. This has a frequency threshold above the frequency of commutator pulses. Again, the threshold will not be a precise cut-off frequency, but in practice, as the noise66has a frequency which is very much higher than the frequency of pulses64, the characteristics of the filter46can readily be selected to reject the noise66, so that the output52, applied by the filter46to the microcontroller54, contains only the commutator pulses64, having rejected the noise66. The pulses, as they appear at52are shown inFIG. 6.

Thus, the arrangement27has recovered the commutator pulses64from the waveform at26, rejecting the lower frequency, mains supply ripple, and the higher frequency noise66. The waveform ofFIG. 6can then be used by the A/D converter56to create a pulse train for counting at58.

The number of commutator pulses created by one revolution of the motor18is fixed by the design of the motor18. The length of travel of the door12for each rotation of the motor18is fixed by the gear ratio of the drive train. Consequently, counting commutator pulses ofFIG. 5provides an accurate and precise measurement of the position of the door12. For example, a practical example may give rise to in excess of fifty commutator pulses per 1 cm of door travel.

However, this analysis assumes that no slippage occurs between the pulley wheels18A and drive belt18B. If any slippage occurs, the motor18may continue to turn without the door12moving the corresponding distance, resulting in an inaccuracy in the commutator pulse count. Any such inaccuracy is unlikely to be significant, in practice, if it occurs over a small part of the range of movement, but may become significant if errors accumulate over a large part of the range of movement. The circuit ofFIG. 3seeks to address this issue.

The circuit70ofFIG. 3is connected at72across the motor18(the terminals72being illustrated inFIGS. 2 and 3). The purpose of the circuit70is to inject pulses into the motor current supply, through the terminals72, for detection by the circuit27ofFIG. 2.

In broad outline, the circuit70includes a Hall Effect sensor74which controls an oscillator76to produce a pulse train consisting of bursts of high frequency oscillation. These pulses are used to control the state of a transistor78to cause current to be drawn or not drawn from the connections72, thus injecting current pulses into the motor current supply sensed at28. This allows information to be sent from the sensor74to the circuit ofFIG. 2without requiring additional wiring connecting the circuits ofFIGS. 2 and 3.

In more detail, the circuit70has a bridge rectifier80drawing power from the terminals72for a power supply at82which provides a positive supply rail84.

The positive supply84is provided to the Hall Effect sensor74at86. The sensor74is also connected to the ground rail at88and provides an output at90. The Hall Effect sensor74is conventional in itself and provides an output90at a voltage mid-way between the rails84,88in the absence of a magnetic field in the vicinity of the sensor74. However, in the event that a north magnetic pole92of sufficient strength faces the sensor74, the output90will drop towards the level of the rail88.

The magnet92is mounted on the pulley wheel18A (not shown inFIG. 3) which is fixed to the shaft16, so that as the pulley wheel18rotates with the shaft16, the magnet92repeatedly passes the sensor74. Since the pulley wheel is fixed to turn with the shaft, this process is not affected by any slippage between the pulley wheel and the drive belt18B.

The output90of the sensor74is applied to the base of a transistor TR1having a collector resistor R11connected to the positive rail84, to form an inverter. A second inverter94provides an output applied to a pulse shaping circuit96. By virtue of the double inversion, the output of the inverter94is high in the absence of a magnet, and drops low as the magnet92passes the sensor74.

Within the circuit96, a NAND gate98has two inputs100. Input100A is connected directly to the common terminal of a parallel capacitor C6and resistor R12, the other terminals of which are connected to the positive rail84. The input100B is connected to the output of the inverter94and, through a diode D1to the common terminal102of the capacitor C6and resistor R12.

Consequently, in the absence of a magnet92, the common terminal102will be high, both inputs100A,100B will be high and the output of the gate98will be low.

When a magnet92passes the sensor74, the output of the inverter94falls. This sends the output of the gate98high but also pulls the common terminal102low. The common terminal102is then held low by the capacitor C6for a period set by the time constant of capacitor C6and resistor R12, so that the output of the gate98will remain high for this period, even if the output of the inverter94goes high during this period. In this example, the period is set at about 100 ms.

Thus, the output of the gate98goes high for a period of about 100 ms, each time the magnet92passes the sensor74.

The output of the gate98is used to control the oscillator76. The oscillator76is a gated free-running pulse generator. The mark-space ratio of the output is controlled by the resistive-capacitive time constant provided by frequency control capacitors76A and resistors76B and by the biasing of diodes76C. Operation of the oscillator76will be apparent to the skilled reader. For the purpose of this description, it is sufficient to point out that the output of the oscillator76is from a gate104which is in turn controlled by the output of the gate98. The output of the gate98is applied by means of a series RC time constant circuit C7, R13. Capacitor C7initially pulls the common terminal99high, with the output of the gate98. The voltage at99then decays with a time constant, in this example, of about 12 ms. Thus, each time a magnet passes the sensor74, the output of gate98goes high for about 100 ms and a burst of oscillations, lasting about 12 ms, appears at the output108of the oscillator76.

The frequency of oscillation is set by the component values within the oscillator76and in this example, is set at about 4 kHz.

Thus, each time a magnet92is sensed by the sensor74, a 12 ms burst of 4 kHz oscillation is provided by the output108and applied through an inverter110and series resistor R14to the gate of the transistor78.

Each time a burst of 4 kHz oscillation is received at the base of the transistor78, the transistor78will be switched (at 4 kHz) for a period of 12 ms. This causes current through the resistor R15which is in series with the transistor78and across the bridge rectifier80. Consequently, a 12 ms burst of 4 kHz current is drawn from the terminals72and thus injected onto the current waveform passing through the motor18. The injected bursts of 4 kHz oscillation will therefore appear in the current which is sensed at the sensing resistor28. They will be above the cut-off frequency of the high pass filter38. The cut-off frequency of the low pass filter46is set to be above the oscillation frequency (such as at 6 kHz or above) so that the bursts of oscillation are passed to the microcontroller54. This cut-off frequency is also above the frequency of commutator pulses when the motor is in a fast mode, but that is not important, because fast commutator pulses are ignored by the microcontroller54.

The circuit ofFIG. 3operates only when the motor18is in fast operation, supplied by a relatively high voltage supply. When the voltage drops at72for slow speed operation, insufficient voltage arises for current to be drawn by the Zener diode Z1of the power supply82, and supply to the rail84ceases, shutting down the circuit70.

FIG. 7shows one cycle of the waveform ofFIG. 6on an enlarged scale, and showing a 12 ms burst112of 1 kHz oscillation, superimposed on a commutator pulse64.

Consequently, the microcontroller54is provided with commutator pulses relating to rotation of the motor18, and with high frequency bursts derived from rotation of the shaft16, pulley18A and magnet92. This allows the microcontroller to choose which of these types of pulse to respond to, the significance of which can now be explained with reference toFIG. 6.

FIG. 8shows a single axis120representing the count held by the counter58. The count is derived in part from commutator pulses and in part from high frequency injected bursts. At one extreme of the count range, for example the lowest count, the count indicates the fully closed position at122. At the other extreme count, for example the highest count, the count represents the full open position of the door, at124. Other counts represent speed change positions126A,126B and a reversing position128. Control functions68, within the microcontroller54, can readily identify the occurrence of a count which represents the positions126A,126B,128and issue an instruction at an output68A to cause the speed of the closure member to change, or the response to an obstruction to change, as can now be described.

For example, counts within the region130, between the speed change positions126A,126B represent the door at intermediate positions, i.e. away from its fully closed or fully open positions. Over this region of its movement, It is safe, in normal operating conditions, to move the door12at its faster speed, i.e. by driving the motor18at its fast speed. This corresponds with the production of fast (e.g. 1 kHz) commutator pulses64and the injection of 4 kHz bursts by the circuit70. Over this region of its movement, counting 4 kHz bursts avoids any inaccuracy arising in the count from belt slippage, because rotations of the shaft16are being counted directly. However, the position measurement is coarse. For example, if only one magnet is used, the count represents complete turns of the shaft16. As the door approaches the fully closed or fully open position, the count made by the microcontroller54will Indicate that the corresponding speed change position126A,126B has been reached. When this is detected by the arrangement68, the output68A is changed to reduce the motor18to its slower speed. This switches off the circuit70, and commences slow (e.g. 400 Hz) commutator pulses64. Commutator pulses then continue to occur, at a slower rate, but still retaining the relationship between pulse numbers and distance travelled, subject to slippage. However, the distance between the speed change position126A,126B can be set to be small (much smaller than the length of the mid region130) so that slippage errors do not aggregate to an unacceptable degree. This function ensures that as the door12approaches its extreme positions, it is moving more slowly, so that any impact against end stops etc. is less severe, particularly if these have moved by mechanical misalignment or the like. Thus, this function of causing the speed of the closure member to change as the closure member passes the speed change position126is primarily provided for reasons of reliability, i.e. to reduce the risk of damage to the mechanisms when the extreme positions are reached.

In the region132, between the fully open position and the corresponding speed change position126B, it is appropriate to continue monitoring door position by counting commutator pulses. When the door stops moving, the count may be recalibrated, if any belt slippage has occurred.

Near the fully closed position, various additional safety features are Increasingly desired or required, sometimes by legislation. For example, it is desirable that if the door is obstructed, as it is nearly fully closed, it should stop and reverse to re-open. This ensures that, for example, a trapped limb is released rather than being injured.

The provision of this facility is assisted by the definition of a reversing position128. If an obstruction is encountered while the door is closing, but in the region134, between the reversing position128and the fully open position124, the motor18is stopped and reversed in order to re-open the door. However, if the obstruction is sensed while the door is closing and is in the region136, i.e. between the reversing position128and the fully closed position122, the motor18is merely stopped, leaving the door at the position it has reached.

It is envisaged that the reversing position128can be set so that the gap then left by the door12is smaller than any body part likely to be within the gap, so that a body part would already have been encountered and the door re-opened, before reaching the reversing position128. Thus, an obstruction between the reversing position128and the fully closed position122may be the result of mechanical misalignment, calibration error etc., rather than the presence of a body part, and thus does not require the door to be re-opened.

It can therefore be understood that the reversing position128can be set independently of the speed change position126A,126B, so that the separate requirements of mechanical reliability and safety can be addressed independently.

Furthermore, safety within the region132is enhanced by counting commutator pulses within this region, rather than high frequency bursts. This ensures that position measurement is much finer than in the mid region130, there being many commutator pulses for each turn of the shaft16.

Thus, in addition to making decisions about stopping or re-opening the door, in accordance with the position along the axis120, the microcontroller54also makes decisions about the source of the signals to be counted. That is, the microcontroller54detects when the speed change position126A is reached in either direction, and changes between counting commutator pulses or high frequency bursts, so that high frequency bursts are measured in the region130, and commutator pulses are measured in other regions.

It is an important advantage of the arrangements described above that no wiring, in addition to the motor current supply, is required between the circuits ofFIGS. 2 and 3to allow them to communicate with each other. This simplifies installation.

Many variations and modifications can be made to the apparatus and methods described above, without departing from the scope of the invention. In particular, many different circuit arrangements could be envisaged, other than those shown inFIG. 2. Other divisions could be chosen between analogue and digital portions of the circuit. For example, filtering could be achieved by digital means. Band pass filtering could be used, rather than separate high pass and low pass filtering. The arrangements could be applied to other types of aperture closure members, such as sliding doors, roller shutters, vertical lift doors or high lift doors.