GB2334753A - Barrier drive - Google Patents

Abstract

A barrier has a beam which is moved in the vertical plane for opening and closing in applications such as car parks. Drive is provided by an AC motor (15) which has symmetrically-arranged coils for forward and reverse motions. A main controller (12) delivers full motion signals for either direction, and also low-speed signals in which parts of the main cycle are chopped. Low-speed signals are identified by a braking controller (13) which activates a braking operation in which the signals are converted to identical signals to both coils simultaneously so that they act against each other for fast braking. The braking time is reduced from approximately 1.5 seconds to 0.3 seconds.

Description

"A Barrier" The invention relates to a barrier of the type comprising a control system which controls a motor which in turn drives a beam or gate via a transmission. The beam or gate may move in a vertical plane or in a horizontal plane for the opening or closing movements.

Typically, the beam or gate (hereinafter referred to as a beam) is driven by an ac motor which receives powcr from a mains supply. The power switches are controlled by the drive signals to cause full forward or reverse motion of the motor, and when these signals stop the beam comes to rest by inertia. In some cases the control system delivers signals which cause only part of the power to be delivered to the motor, thus reducing speed. For example, if only half of the mains cycle is delivered to the motor, the speed is reduced to half.

Switching from forward to reverse directions is typically achieved in a balanced single phase motor by a balanced signal phase pole switch.

While this approach is often satisfactory for applications such as gates controlling access to domestic dwellings, problems arise for applications which require intensive use of the barriers such as public car parks. For each use, the time required for stopping can take in the region of 1.5 to 2.5 seconds, thus causing a long cycle time and limiting throughput.

Another disadvantage is that it is difficult to control exactly the stop position of the beam.

It is therefore an object of the invention to provide a barrier which has cycles of shorter duration.

Another object is to provide more accurate open and closed positions.

According to the invention, there is provided a barrier comprising a control system controlling a motor, in turn driving a beam via a transmission, wherein, the motor is an AC motor having a coil for forward drive and a coil for reverse drive, the coils being symmetrically arranged, and the control system comprises means for delivering a full drive signal to one coil at a time for full speed motion, and for delivering similar signals to botn coils simultaneously for braking.

By providing a motor having a symmetrical coil arrangement and by delivering control signals simultaneously to both coils for braking, the coils act against each other to cause the beam to brake very quickly.

It has been found that motor life is not affected to a significant extent if the braking signals are delivered for a time period in the range of 100 to 500ms, and this time is preferably approximately 300ms In one embodiment, the braking signals are pulsed. This helps to minimise heat generation in the coils.

Preferably, the braking signals are pulsed with on periods of one-third of each cycle.

In one embodiment, the control system comprises a main controller comprising means for delivering full speed and low speed drive signals, and a braking controller comprising means for monitoring signals from the main controller and for automatically generating the braking signals when low-speed signals are detected.

In the latter embodiment, the low speed signals may be out-of-phase pulses to the two coils.

In one embodiment, the control system comprises an RC circuit for setting the duration of the braking signals.

In one embodiment, the braking controller comprises means for pulling output terminals to ground during the balance of time between the braking duration and the low speed duration.

In the latter embodiment, said means may comprise a voltage divider circuit.

In a further embodiment, the motor is permanent capacitor induction motor.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a perspective view from above of a barrier of the invention; Fig. 2 is a block diagram of a control system of the barrier; and Fig. 3 is a circuit diagram of the braking controller of the control system.

Referring to the drawings and initially to Fig. I there is shown a barrier 1 of the type for controlling entrances to car parks. The barrier 1 comprises a support structure 2 having a base plate 3 secured to the ground. A beam 4 is rotated in a vertical plane by a bracket 5.

The bracket 5 is driven by a control system 10 which controls an AC motor 15 which in turn drives the bracket 5 via a transmission, not shown. In this embodiment, the transmission is of the type comprising a crank wheel which is rotated 1800 to move a con rod which in turn is connected to the bracket 5. However, the transmission may be of any other suitable type.

Referring to Fig. 2, the control system is indicated by the numeral 10 and it comprises a power supply 11 which receives a main supply input and delivers DC to a main controller 12 and to a braking controller 13. It also delivers AC to power switches 14 for an AC permanent capacitor induction motor 15. The power supply also delivers AC to accessories such as a coin mechanisms.

Operation of the control system 10 is now described with reference to Fig. 3 which illustrates the braking controller 13 in more detail. The AC motor 15 is a single phase permanent capacitor induction motor having a full load speed of 2800 rpm, an outlet power of 150 Watts, a starting torque full load of 80%, a 1.2 Amp current rating and an 8.4 micro Farad capacitance. The coils are symmetrical, one for forward movement and the other for reverse movement.

The main controller 12 is configured to generate the following signal outputs: - A continuous signal for either of the windings at any one time for full forward or full reverse motion.

- No output signal for the motor to be stationary.

- Out-of-phase signals at one third of mains frequency one delivered to both windings for low speed motion. For example, pulses are delivered to the forward coil and pulses delayed by 1200 pulses are delivered to the reverse coil.

These signals can be either delivered directly to the power switches 14 as indicated by interrupted lines, or they may be intercepted by the braking controller 13. The braking controller 13 is configured to allow the full drive signals to be routed directly through, however, it uses the pulsed low-speed signals as a trigger to generate a braking signal for the power switches 14.

In more detail, the control signals from the main controller 15 are received at terminals Tl and T2. T1 receives the signals for one coil and T2 for the other. When the pulsed low-speed signals are received, the comparators IC 1, IC2, IC3, and IC4 cause the potential at position A in the circuit to go high. This transition is routed through the capacitor C3, thus causing the potential at point B to also go high. However, the level at B remains high only for the duration of charging of the capacitor C3 and this time is set by the values of C3 and a resistor R11 which connect point B to ground. A comparator IC5 receives a reference input at its negative terminal, this being set by the value of the resistors R5 and R6. While the potential at B remains higher than this reference, the output potential at point C remains high. Thus, a consistent high output level is maintained at C for the duration of charging of the capacitor C3. This signal is broken into pulses by the comparator IC6. The comparator IC6 receives as an input the negative transitions at the terminals T1 and T2 and these cause the output of 1C6 to go low, thus causing it to act as a sink to pull D, and therefore C don. This causes the signal at C to be a series of pulses which are present for the duration of the period set by the capacitor C3 and the resistor R11. These pulses appear at the output terminals T3 and T4 which are delivered to the power switches 14 simultaneously for control of both of the coils.

Thus, the coils act against each other simultaneously to cause very quick braking. The duration of the braking pulses is 1 sums, and there are typically 20 for each braking action.

It has been found that a braking signal time duration of 100 to 500 ms is effective, and a duration of 300 ms is particularly effective. However, the total time period for the low speed signals may be as much as 1.5 seconds and the balance of the time between 0.3 and 1.5 seconds is handled by pulling the voltage at the output terminals T3 and T4 to ground.

This is achieved by operation of the comparators IC7 and IC8 which perform this function comparing the voltages at points E and F. The voltage at point E is half that at point A i.e. +V/2 during the 1.5 second reduced speed period, and 0V otherwise. The voltage at point F is one tenth of +V, except when it is pulled high to +V by point D via the diode D7. Therefore, the voltage at point F is higher than point E except during the balance of the reduced speed period after the 0.3 second braking time has expired.

When full drive signals are received at the input terminals T1 and T2, these are routed directly to the power switches 14 by resistors S and T, shown in Fig. 3.

It will be appreciated that the invention provides for very fast braking, thus greatly reducing the cycle time for a barrier. This is very important as it dramatically increases the throughput for applications such as car parks. At the same time, however, the life of the motor is not reduced as extra load and heat generation is minimised because the braking signals are pulses.

The invention is not limited to the embodiments described but may be varied in construction and detail within the scope of the claims.

Claims (12)

1. Claims 1. A barrier comprising a control system controlling a motor, in turn driving a beam via a transmission, wherein, the motor is an AC motor having a coil for forward drive and a coil for reverse drive, the coils being symmetrically arranged, and the control system comprises means for delivering a full drive signal to one coil at a time for full speed motion, and for delivering similar signals to both coils simultaneously for braking.
2. 2. A barrier as claimed in claim 1, wherein the braking signals are delivered for a time period in the range of 100 to 500ms.
3. 3. A barrier as claimed in claim 2, wherein the braking signals are delivered for a time period of approximately 300ms.
4. 4. A barrier as claimed in any preceding claim, wherein the braking signals are pulsed.
5. 5. A barrier as claimed in claim 4, wherein the braking signals are pulsed with on periods of one-third of each cycle.
6. 6. A barrier as claimed in any preceding claim, wherein the control system comprises a main controller comprising means for delivering full speed and low speed drive signals, and a braking controller comprising means for monitoring signals from the main controller and for automatically generating the braking signals when low-speed signals are detected.
7. 7. A barrier as claimed in claim 6, wherein the low speed drive signals are out-of phase pulses to the two coils.
8. 8. A barrier as claimed in claims 6 or 7, wherein the braking controller comprises means for pulling output terminals to ground during the balance of time between the braking duration and the low speed duration.
9. 9. A barrier as claimed in claim 8, wherein the said means comprises a voltage divider circus .
10. 10. A barrier as claimed in any preceding claim, wherein the control system comprises an RC circuit for setting the duration of the braking signals.
11. !1. A barrier as claimed in any preceding claim, wherein the motor is a permanent capacitor induction motor.
12. 12. A barrier substantially as described with reference to the drawings.