IMPROVEMENTS IN WINDSCREEN WIPERS

Abstract: A straight line wiper of the kind where a belt or chain drive (1) on two pulleys or gear wheels (2, 3) and driven by a motor (10), drives a wiper (4, 5) along a straight line path driven by movement of the upper flight of the belt (1) in one direction and by the lower flight in the reverse direction between two ends of strok positions (6, 7). The apparatus includes a motor speed profile arrangement which reduces the speed of the motor (10) as the wiper (4, 5) approaches each end of stroke position (6, 7) and increases the motor speed as the wiper (4, 5) moves away from each end of stroke position (6, 7).

Description: Improvements in Windscreen Wipers This invention relates to a straight-line windscreen wiper of the type used on large marine vessels. A straight-line wiper offers the advantage of a swept area that can cover substantially the whole window being wiped. Also it can be constructed in a robust form so as to deal with extreme conditions. The wiper generally uses a continuous drive means in the form of a belt which runs between two equal sized pulley wheels. Alternatively the continuous drive means may be a chain running on sprocket wheels. The blade of the wiper is fixed to a wiper carriage which runs and is guided in a casing, and which is attached by an appropriate linkage to the belt. One of the wheels is free to rotate on its bearings whilst the other is driven by an electric motor, or both may be driven, so that the carriage moves in a linear path along the casing. Referring to Figure 1 of the accompanying drawings the motion of the carriage is reversed at each end (a, and b) of stroke by the motion of the carriage attachment point being transferred from the upper to the lower flight and vice versa. The motor is generally run at one speed , so the velocity V of the carriage (and hence of the wiper blade) is as shown in Figure 1 of the drawings accompanying this Patent Application. The rate of change of velocity f (i.e. acceleration) is shown in Figure 2. The value at the end of stroke is large, typically 5g. The large value is currently accommodated by the use of damping mechanisms, and by limiting the size of the wiper arm and blade (and hence inertia) to values such that there is an acceptable life and acceptable levels of the physical manifestation of acceleration and deceleration shocks. The problem of large start up and slow down shock is particularly acute with heavy duty marine wipers, be cause of the extreme conditions which are encountered. In particular the system needs to be extremely robust and a high pressure has to be applied to the wiper blade to ensure reliable operation in adverse weather conditions which are accentuated by salt or icing. In accordance with the present invention there is provided a heavy duty wiper device which includes a continuous drive means operating over spaced wheels, which is arranged to carry a wiper carriage to cause it to travel in a to and fro motion between said spaced wheels, and a drive motor for driving one of said spaced wheels, characterised by speed profiling means for controlling the speed of said motor, said speed profiling means being arranged to control the motor speed so as to perform an operational to and fro cycle where in a region at each end of the travel of said wiper carriage the motor speed is, over a selected period of time, smoothly increased from a low speed to an operational speed as it leaves each end of travel position and is smoothly reduced from the operational speed to the low speed as it approaches each end of travel position. A variable speed of operation is often provided in current designs. This is achieved by crude (open-loop) regulation of the motor speed using a speed setting control which reduces the average current fed to the motor (generally either dc or series-wound ac). In conjunction with the essentially constant wiper torque demand, this results in a lower average speed. By sensing the position of the carriage, it is possible to provide a profiled decrease of motor speed on approach to an end of motion, and a subsequent increase back to the normal speed for the motion across the main travel. Most systems also incorporate a 'park' position sensor, such that on reaching that end of stroke the motor is caused, in a simple control circuit, to be stopped. One simple method of achieving the smoothed action according to the invention is to make use of this park position sensor P to engage a speed demand profile as shown in Figure 3. In a proposed embodiment, this profile is generated using a microcontroller, whose output drives an E 2 -potentiometer. By sensing the relative timing of the end of its time based profile and the occurrence of another park sensor signal, the system can adjust itself so that the end of its profile is kept close to the start of the next profile. Alternative possibilities are as follows: 1. A motor with encoder (simple pulse generator) enhances the accuracy of the position of speed change and can be used for more precise closed-loop motor speed control. One physical carriage position sensor is still needed. 2. A toothed belt in combination with 1 above would give even more certainty of position of the carriage. A sensor picking up the motion of the belt (optically from the tooth profile of the belt or the pulley) can be used in place of the motor encoder and thus offer the most direct positional data. 3. Schemes 1 or 2 can be used in combination with an inverter drive i.e. a drive that controls the speed of the (lower cost and more rugged) induction motor, by the alteration of supply frequency. Usually this will comprise a rectifier to convert the supply to DC and a solid state inverter which~converts the supply back to AC at a variable frequency. 4. The profile of the speed can be made to simulate simple harmonic motion, and thus give the appearance of a natural oscillating motion with smooth acceleration to a maximum position followed by a corresponding smooth deceleration. In summary the invention provides control of linear blade speed local to the end of travel on a straight line wiper thus reducing the end of stroke shocks, thereby allowing larger blades and arms to be used for a given casing and carriage mechanism, thereby extending the range of capability, and furthermore reducing the noise generated and enhancing the life of the wiper system. Control of speed throughout the travel of the wiper can be used to generate simple harmonic motion, or merely at the end of travel zones. For a fuller description of existing straight-line wipers reference is made to our Wynstruments patent specifications, for example No. GB 1,490,597. An embodiment of the invention will now be described by way of an example with reference to Figure 4 of the drawings which shows a schematic diagram of a wiper mechanism incorporating the present invention. Continuous drive means 1 in the form of a continuous belt operates over spaced pulley wheels 2 and 3 to carry a wiper carriage 4 including a wiper blade 5 to cause it to travel in a to and fro motion between end of travel points 6 and 7 while running on a slide track (not shown) . The mechanism is essentially as described in our earlier British patents numbers 1490597 and 1502199 utilises a motor 10 which drives the right hand pulley 3. With this arrangement the upper flight of the continuous belt 1 drives the carriage from left to right until it reaches and end of travel position 7 when it is brought back on the lower flight of the belt until it again reaches the end of travel position 6. A park sensor 8 in the form of a reed switch is located at the first extremity position 6 and is operated by a magnet 9 carried by the carrier 4. In a normal wiper mechanism the reed switch 8 is wired in parallel with a park switch which when opened enables the carrier to continue movement until it reaches its end of travel at which point the reed switch opens and current to the motor is cut off. The present invention makes use of this reed switch 8. At this point it should be noted that the reed switch 8 is shown at the left hand end of the travel, however it could be at either the free running left hand end or the right hand driven end, since the motions at each end are the same and a continuous symmetrical speed profile occurs in each direction of travel. The speed profiling means 10 is shown schematically as a block diagram. A central processing unit CPU, into which a timer T and the reed switch output are fed, generates the speed profile in the manner previously discussed and this profile is fed to an inverter I which then feeds the speed controlled supply from an AC supply to the motor 5 . Referring to Figure 3, the reed switch 8 provides a signal at the start of the to and fro cycle and again at the end, i.e. when the carrier again reaches the position 6 area, The difference between the actual time of the signal S and the adjacent minimum point in the cycle is then used to correct the time period for the next cycle, so that synchronisation is maintained.

Claims: CLAIMS 1. A heavy duty wiper device which includes a continuous drive means operating over spaced wheels, a wiper carriage driven by said continuous drive means so as to travel in a to and fro motion between first and second end of travel positions, and a drive motor for driving at least one of said spaced wheels, characterised by speed profiling means for controlling the speed of said motor, said speed profiling means being arranged to control the motor speed so as to perform an operational to and fro cycle where in a region at each end of the travel of said wiper carriage the motor speed is, over a selected period of time, smoothly increased from a low speed to an operational speed as it leaves an end of travel position and is smoothly reduced from the operational speed to the low speed as it approaches an end of travel position. 2. A heavy duty wiper device according to claim 1 which includes a park sensor for sensing an end of travel position of the carriage to enable the wiper to stop at a park position, characterised in that said park sensor is arrange to synchronise operation of said speed profiling means. 3. A heavy duty wiper device according to any preceding claim characterised in that said speed profiling means is arranged to provide a speed profile where in said operational cycle the motor speed increases smoothly from a low speed at a first end of travel position to an operational speed, continues at the operational speed until approaching a second end of travel position where it smoothly reduces to a low speed at the second end of travel position and then repeats the same speed profile as it returns from the second end of travel position and again reaches the first end of travel position. 4. A heavy duty wiper device according to claim 1 or 2 characterised in that said operational cycle is arranged to be in a simple harmonic motion. 5. A heavy duty wiper device according to any preceding claim having switching means for changing between a plurality of operational speed modes, for example intermittent wipe, high speed, intermediate speed and self park, each of which uses at least a part of said operational cycle. 6. A heavy duty wiper device according to any preceding claim characterised in that said speed profiling means includes AC supply means and an inverter for controlling the speed of said motor in accordance with said operational cycle.

Inventors: ELMHIRST JOHN, KIRKBY DENIS JAMES, ELMHIRST, JOHN, KIRKBY, DENIS, JAMES
Applicants: ELMHIRST JOHN, KIRKBY DENIS JAMES, WYNN MARINE LTD, ELMHIRST, JOHN, KIRKBY, DENIS, JAMES, WYNN MARINE LTD.
Application year: 1995
Main classification: B60S1
IPC codes: B60S1