GB2442246A

GB2442246A - Light controlled pedestrian crossing with tactile indicator

Info

Publication number: GB2442246A
Application number: GB0619053A
Authority: GB
Inventors: Richard Keith Duley
Original assignee: Radix Systems Ltd
Current assignee: Radix Systems Ltd
Priority date: 2006-09-27
Filing date: 2006-09-27
Publication date: 2008-04-02
Also published as: GB0619053D0

Abstract

A box for a light controlled pedestrian crossing comprises a push button, a visual signal module 19 comprising direct current (DC) operated light emitters and a tactile signal module 18 comprising a DC electric motor 14 that drives a rotary tactile indicator (fig 1, 12) projecting from the box. In use alternating current (AC) power is applied to input terminals 16, and circuitry to operate the tactile indicator motor 14 and the visual signal module 19 share a common component, at least a common rectifier BRI. The DC motor circuitry may include a switched mode power supply, a current limiting network to limit torque, voltage limiting components D1, D2, and a switch TR1 to enable free movement of the tactile knob (fig 1, 12). The box enables economies to be made when tactile and visual indicators are to be operated from the same AC supply.

Description

LIGHT CONTROLLED PEDESTRIAN CROSSINGS

This invention relates to tight controlled pedestrian crossings.

It is wefl known that visually handicapped pedestrians have difficulty in determining a safe crossing period at complex traffic signal controlled pedestrian crossings. At simple installations an audible indicator is effective but where more than one crossing exists in a limited area dangerous ambiguities may result The Highways Agency have, therefore, issued a specification (TR0157) describing a tactile indicator which can be installed in the existing pedestrian push button boxes. This tactile indicator comprises an electric motor which rotates, specifically, a knurled cone projecting from the bottom of the push button box to indicate safe crossing conditions.

In a known arrangement. the electric motor is supplied with D.C. power by a power supply connected in parallel with a lamp for illuminating a visual invitation to cross signal at a far side signal box. The existence of a far side signal box on one side implies that close to (usually above) the push button box on both sides of the crossing, is a signal box which acts as the far side signal box for the other push button box. The far side visual signals are run on 230 v A.C. So, partly as to reduce the voltage supplied to the push button boxes, the power supply for the motor is located in the local signal box and appropriate 0 C is run to the push button box from the signal box.

A problem with the conventional far side signal box is that some people become confused when the visual invitation to cross signal changes when they are only part way across the crossing, despite the provision of a flashing signal intended to mean do not start". A proposal described in GB-A-2 379 287 takes advantage of a recent departure in the form of a near side signal box. Since this cannot be seen once the pedestrian has started, the confusion is avoided. This specification discloses a nearside push button box or push button and signal box for a light controlled pedestrian crossing, containing a unitary tactile indicator comprising a 0 C. electric motor driving a rotary tactile indicator projecting from the signal box, and a power supply connected to receive A.C. power in parallel with a light emitter for illuminating a visual safe to cross signal, and to supply D.C. power to the electric motor. This arrangement avoids the wiring necessary with a remote power supply.

The invention is based on the realisation that economies may be made in the component count.

In accordance with the invention, one or more boxes for use on one side of a light controlled pedestrian crossing, contains, or together contain, a pedestrian demand push button, a visual signal module and a tactile signal module, the visual signal module including one or more D.C. operated light emitters and, in use, converting A.C. power applied to input terminals, to operate the light emitter(s) to illuminate a visual invitation to cross signal, and the tactile signal module having a D.C. electric motor drivingly connected to a rotary tactile indicator projecting from its box and, in use, converting A.C.

power applied to said input terminals, to drive said motor to rotate the tactile indicator, said visual signal module and tactile signal module sharing common components including at least a common rectifier for connection to said input terminals.

The tactile signal module preferably includes a switched mode power supply having a controlled output voltage to define the offload speed of the motor.

The one or more boxes preferably include a network or device for limiting current drawn by the motor to, and maintaining said current, when limited, at a chosen value.

The switching rate of the power supply is preferably at least 150 kHz.

A series parallel zener diode arrangement is preferably included, to limit the peak input voltage to the switched mode power supply, to a value which the power supply can tolerate.

A switching device is preferably included in series with the motor, the switching device being operative to close when power is supplied to the motor and to open when power is not supplied to the motor. This ensures the tactile indicator can be "twirled" in both directions when power is not supplied to the motor. I'

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a pictorial view of a nearside signal box for a light controlled pedestrian crossing; Figure 2 is a circuit diagram of a tactile indicator embodying the invention, for a nearside signal box; and Figure 3 is an alternative circuit diagram to that shown in Figure 2.

Referring to the drawings, a light controlled pedestrian crossing has a near side signal box 2, for indicating when it is safe for a pedestrian to cross the road. The box 2 is mounted on a pole 4 at a convenient height such that a pedestrian desiring to cross can and operate a push button 6. As is conventional, operation of the push button initiates a process which results in 48 v A.C. being supplied to a lamp to illuminate a green sign 8 of a person walking, inviting a pedestrian to cross. After a period power to the green sign 8 is cut and 48 v A.C. is supplied to a lamp to illuminate a red sign 10 of a stationary person, indicating it is not safe to cross. Although the illumination of the green sign may be accompanied by a audible signal, in cases where that might be ambiguous to a visually impaired pedestrian, a tactile indicator can be provided. This has a knurled frusto-conical knob 12 projecting from the box 2 and is rotated by an electric motor 14 through a gear box, not shown, when it is safe to cross.

To this end, 48 v AC. is supplied to the input terminals 16 of a tactile signal module 18, which includes the motor 14, gear box and knob 12. The tactile signal module shares a full wave bridge rectifier BR1 with a visual signal module 19, which includes other components of a switched mode power supply to convert the rough DC output of the rectifier BR1 to supply LEDs, not shown, to illuminate the green invitation to cross sign.

Returning to the tactile signal module 18, the input A.C. is rectified by the rectifier BR1. Rectified A.C. is fed via a voltage limiting zener diode combination Dl, D2 and via a parallel smoothing capacitor Ci to the input pins 7 and 6 of an LM 2594 integrated circuit switched mode buck regulator lCl. This is physically smaller than a transformer-based power supply, which is important since the space inside the box 2 is limited, and dissipates less power. The output voltage of the regulator appears on pin 8 and is smoothed by a pi network comprising a parallel fly back schottky diode D3, a series inductor Li, and a parallel capacitor C2. The regulator ICI operates at a switching rate of 150 kHz which facilitates the use of a smaller value inductor Li and capacitor C2, than would provide adequate smoothing if a lower switching rate were used. Naturally, an even higher switching rate would facilitate of even smaller values. Use of smaller values of inductance and capacitance facilitate the use of physically smaller components which is important again, since the space available inside the box 2 is limited.

As is conventional, the smoothed D.C. output voltage at node 20 is controlled by a feedback loop. Thus a potential divider consisting of resistors R2 and R3 provides a proportion of the voltage at node 20 to pin 4 of ICI. A capacitor C3 provides a differential component to the feed back signal.

The values of R2 and R3 are chosen so that the voltage at node 20 provides an off load motor speed to drive the knurled knob 12 at a speed within the range required by the Highways Agency specification TR 0157. When the motor is loaded, by a person grasping the knurled knob 12, the torque generated by the motor 14 is limited by controlling the current it draws. The torque at the knob 12 is thus limited to that allowed by TR 0157.

To this end, node 20 is connected to the input pin IN of a LM3I 7T voltage control integrated circuit 1C2. The output pin OUT of 1C2 is connected to the motor 14 via a series resistor R4. Node 24, between the resistor R4 and the motor is connected to the feedback pin ADJ of lC2 which thus acts to maintain the voltage across R4 at a predetermined value, and thus a predetermined current, as long as there is sufficient voltage at node 20 to generate that current. On no load, therefore, the voltage at node is insufficient and the current falls below the predetermined current, the motor speed being limited by the voltage at node 20. As the motor is progressively loaded, the current through resistor R4 increases until it reaches the predetermined limit, when 1C2 maintains it at that value even if the motor stalls. The reduction of the voltage across the motor, due to the drop across resistor R4 as the torque, and thus current, increases is not so great as to fall outside the 20% tolerance set by TR 0157 The level of the current, and thus the torque, is set by the value of R4.

Back to back zener diodes D4 and D5 limit the voltage which could be generated by manual twirling of the knob 12, so as to protect the circuit especially against high reverse bias.

If a visually impaired pedestrian grasps the knob 12 when it is not rotating, it is common for her or him to reinforce her or his perception that the knob is not rotating by twirling it manually. It happens in practice that the direction in which it is natural to twirl it is opposite to the direction in which it is driven by the motor 14. Unfortunately, this forward biases diode 03 which provides a low impedance circuit for the e.m.f. generated by the manually rotated motor. This leads to a rather high level of torque at the knob 12.

In order to ameliorate that effect a NPN switching transistor TR1 has its collector emitter path connected in series with the motor 14. The base is connected via a resistor R5 to node 20, so that when the 48 v signal is applied to terminals 14, 16 and node 20 is at its operating voltage, the transistor TRI saturates allowing the motor to run. When, however, no 48 v signal is applied to the terminals 14, 16 so that node 20 is not at its operating voltage, (reverse) twirling the knob 12 and thus the motor 14, reverse biases the transistor TR1 opening the circuit through 03 and preventing the high torque at the knob 12.

The tactile signal module 18 and the visual signal module 19, may be contained by the same nearside box 2, in which case the modules may share a common circuit board.

In some cases it may be appropriate for the two modules to share other components, e.g. a switched mode power supply. It will generally be necessary for the tactile signal module to have its own current limiting network.

In some arrangements, nearside visible signals are provided in a box separate from the push button box. In that case the distribution of the components between the two boxes may be varied. For example, D.C. to drive the motor or the LEDs directly may be supplied from one box to the other. In an alternative the rough DC output from the rectifier BR1 may be supplied from one box to the other.

In Figure 3, components correspond to those identified by the same references in Figure 2. In Figure 3 the rectified voltage from BRI is fed to a feedback voltage control network. A voltage limiting combination of a resistor R8 and zener diode ZD5 removes any high voltage transients from the input and feeds a limited voltage to the IN pin of a voltage regulator 1C3. The resistor R8 also limits harmonics caused by the remaining circuit being non linear. The voltage on the OUT pin is smoothed by the capacitor Cl and fed back to the ADJ pin of the regulator lC3 via a voltage divider comprising resistors R6 and R7, to control the output voltage. Any high voltage instability is limited by the capacitor C4.

A diode D2 has been added in series with the current measuring resistor R5. This increases the feed back gain so reducing the voltage swing (and thus change in the motor speed) before the current limit begins.

Claims

CLAIMS: 1. One or more boxes for use on one side of a light controlled

pedestrian crossing, said one or more boxes containing, or together containing, a pedestrian demand push button, a visual signal module and a tactile signal module, the visual signal module including one or more D.C. operated light emitters and, in use, converting A.C. power applied to input terminals, to operate the light emitter(s) to illuminate a visual invitation to cross signal, and the tactile signal module having a D.C. electric motor drivingly connected to a rotary tactile indicator projecting from its box and, in use, converting A.C. power applied to said input terminals, to drive said motor to rotate the tactile indicator, said visual signal module and said tactile signal module sharing common components including at least a common rectifier for connection to said input terminals.
2. One or more boxes, as claimed in claim 1, wherein the tactile signal module includes a switched mode power supply having a controlled output voltage to define the offload speed of the motor.
3. One or more boxes as claimed in claim 1 or 2, including a network or device for limiting current drawn by the motor to, and maintaining said current, when limited, at a chosen value.
4. One or more boxes as claimed in claim 2 or claim 3 when dependent on claim 2, wherein the switching rate of the power supply is at least 150 kHz.
5. One or more boxes as claimed in claim 4, including an arrangement, to limit the peak input voltage to the switched mode power supply, to a value which the power supply can tolerate.
6. One or more boxes as claimed in claim 2 or any preceding claim dependent thereon, including a switching device in series with the motor, the switching device being operated to close when power is supplied to the motor and to open when power is not supplied to the motor.