BACKGROUND OF THE INVENTION Rear view mirror assemblies, and in particular wing mirrors are normally designed so that the position of the mirror can be adjusted from within the vehicle. A pair of motors are normally provided within the mirror head which adjusts the mirror about a vertical and a horizontal axis.

Another mirror assembly, which overcomes the need to incorporate adjustment motors within a mirror head is a mirror known as a mono-axis mirror. In this design, driver adjustment is provided only via movement of the mirror head with respect to the vehicle mounting bracket. This is normally about a substantially vertical axis.

The need for adjustment of the mirror about a horizontal axis can be avoided by positioning the mirror so that for a majority of drivers there is no need for adjustment about a horizontal axis. Such a mirror is described in British Patent Appln No. GB 9724211.9.

Regardless of whether the design is a mono-axis mirror, or a conventional dual-axis mirror adjustment, it is desirable to enable a mirror or mirror head to be returned to a preset position. In the case of a mono-axis mirror, if the mirror is moved from a parked position where the mirror head is adjacent the motor vehicle, then it would be desirable to return the mirror head to the required position for a particular driver. In addition, it would be desirable to store several positions for different drivers who may use that vehicle.

In the case of mirrors having adjustment about horizontal and vertical axis, it would be desirable to store several positions of the mirror for different drivers.

One problem associated with electric motors and associated gear drive trains is backlash within the gears which is difficult to totally eliminate. This problem is addressed in the abovementioned British patent specification. Accordingly, the invention needs to take into account gearing backlash to ensure that the mirror is returned to the precise predetermined position.

The invention disclosed in this specification also includes means to electronically control, in a preferred embodiment, the mirror movement mechanisms referred to above and includes the measurement of the angle of rotation of the reflective element; controlling the speed of adjustment such as high speed for backlash take up and parking or low speed for manual adjustment; end of travel detection and motor de-energisation control; reverse motor actuation once the desired reflective element location has been reached; and storage of mirror location settings with recall either when a new vehicle user requires their particular setting or following a power fold operation thus restoring the mirror to its previous location after being in the fold-in parked position.

BRIEF DESCRIPTION OF THE INVENTION In one broad aspect of the invention, a direct current motor speed control method comprises the steps of measuring the back electromotive force (EMF) of a rotating portion of a motor, translating said back EMF to an angular velocity and comparing said velocity with a desired velocity and dependant on whether the velocity is higher or lower than the desired velocity adjusting the period of on-time of the current pulse driving the motor.

In a second broad aspect of the invention, a motor speed controller comprises a direct current motor, a back electromotive force (EMF) detector having a voltage output representative of the back EMF of said motor; controller means for translating said voltage into a desired angular velocity and motor drive means controlled by said controller means for adjusting the angular velocity of said motor to a desired angular velocity.

In a third broad aspect of the invention, a controller for a direct current motor used to control the position of a first member relative to a second member comprises a motor pulse conditioner; and a motor pulse counter, wherein said controller counts motor pulses in a respective direction and determines a position of said first member relative to said second member and said controller provides rotations of said motor in a predetermined direction to locate said second member relative to said first member.

In a fourth aspect of the invention said controller further determines the condition of said motor relative to a previous condition and to determine whether the motor is stalled, stationary or being driven in one or other direction and thereby determine the position of said first member relative to said second member.

In a fifth aspect of the invention, said motor is coupled to said first member by mechanical coupling means having backlash.

In a yet further aspect of the invention said controller provides predetermined rotations of said motor in a predetermined direction to engage and disengage said mechanical coupling to and from said first member.

In a sixth aspect of the invention, said controller provides rotations of said motor in a predetermined direction to take up mechanical backlash of said mechanical coupling between said motor and said first member.

Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. These embodiments are illustrative, and are not meant to be restrictive of the scope of the invention. Suggestions and descriptions of other embodiments may be included but they may not be illustrated in the accompanying figures or alternatively features of the invention may be shown in the figures but not described in the specification.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 depicts a motor driver circuit; Fig. 2 depicts a controller processor circuit; Fig. 3 depicts a wiring loom arrangement between user controls and interface circuitry; Fig. 4 depicts user control interface circuitry; and Fig. 5 depicts a motor pulse detector and conditioner.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION A permanent magnet DC variable length driven electric motor is typically used to actuate the mechanism of a vehicle rear view mirror. When the rotating portion of such a motor is rotating as a result of the application of pulses of current, the motor also generates a voltage that is proportional to its angular velocity, known as its back EMF. Thus during the time the current pulse is not being applied, a back EMF is generated by the motor which is proportional to the angular velocity of the rotating portion of the motor.

The back EMF of the motor can be measured and using a calibration table the motor's angular velocity can be determined and compared with a desired angular velocity of the motor. If for example measured back EMF corresponds to an angular velocity higher than that desired, the on-time of the current pulse driving the motor can be reduced the next time the motor is energised. Correspondingly, if the measured back EMF is indicative of a lower than desired angular velocity of the motor, the on-time of the current pulse driving the motor is increased.

This closed loop measurement and control technique is not affected by the load on the motor. The magnitude of back EMF is generated merely by the angular velocity of the motor and not the amount of work it is doing.

Thus the circuits depicted in Figs 1 and 2 are one embodiment of the above described closed loop measurement and control arrangement of a DC motor. A motor (not shown) is connected between the motor A line and motor B line. Since the motor may rotate in either of two directions, motor A and B lines are bi-polar in operation.

The motor driver circuit (Fig. 1) primarily comprises an integrated circuit U1 and interface components which are under the control of integrated circuit U2 in Fig. 2.

When the motor driver (Fig. 1) makes the motor A line positive and motor B line negative current flows from motor A line through the motor to motor B line for the on-period of the driving pulse. Back EMF occurs causing motor A line to remain positive with respect to motor B line and the amplitude of this back EMF voltage appears as an input to the micro controller U2 via R14 (Fig. 2). D5 (Fig. 1) provides a return path for the voltage amplitude measurement. D4 (Fig. 2) protects the micro controller U2 from over voltage and C12 acts as a low pass frequency filter to block spurious high frequency voltage fluctuations not related to back EMF.

An A to D converter in the micro controller provides a conversion of the analog voltage magnitude into a digital representation which can be used to determine what adjustments should be made to the next driving pulse. The code to perform the function of determining the adjustment direction and magnitude of the angular speed magnitude of the motor also uses inputs from predetermined values as well as user operable switches and also depends on whether the motor is being manually or automatically controlled. For example, full speed operation in the reverse direction is required to promptly take up backlash or alternatively during movement of the mirror for fold-in or out operation preset speeds can be used. In contrast, the user may use a control switch which provides motor speed signals proportional to the position of the switch thus the desired speed is variable during a manual adjustment operation. Alternatively, a fixed low speed may be used when the control switch is activated. Switches SW1,2 and 3 (Fig. 3) provide this type of input data to the micro controller U2 (Fig. 2) via inputs PB1,2 and 3 respectively.

A feature of this embodiment of the invention is the ability to automatically adjust the mirror housing and reflective element in the housing to a predetermined position for varied purposes including fold-in and fold-out associated with "parking"the mirror housing, restoring the reflective element to its position following a parking fold-in or out operation; or restoring the reflective element to a particular user desired location.

To achieve this function the apparatus must be capable of not only measuring back EMF as described previously but of position detection storage and recall plus position locking once the location of the reflective element has been reached.

Permanent magnet DC motors comprise two or more coils in a permanent magnetic field and plural brushes to provide a conduction path to the rotating coils of the motor (rotor). DC motors have other like configurations of stators and rotors (eg the stator may have the coils not the rotor) but in general a pulse of current is required to be applied to each successive coil to energise them in sequence to create the motive force which rotates the shaft of the motor. The number of pulses per complete revolution of the shaft is directly proportional to the number of coils in the motor and is not related to the load or speed of the motor.

Pulses of varying duration (pulse width modulation) are required to drive the motor.

Thus the angular displacement of the shaft of the motor is proportional to the number of commutator pulses in a given time provided that the rotation of the shaft is in the same direction during that given time.

The amount of current provided to the motor will also vary but is directly proportional to the work being done by the motor (ie the revolutions per minute of the motor shaft may be small but the high current being drawn is indicative of the high torque being provided by the motor shaft to operate the mechanical elements of the mirror assembly).

Current variations can also be detected by direct measurement of the current or detecting rapid decreases in current consumption of the motor.

A pulse separator (all of Fig. 5) may be required to enable accurate discrimination between commutation pulses and current consumption pulses caused by load variation as all current pulses relate to current consumption whether they are commutating or not.

In this embodiment, when the motor is energised by the motor controller chip U1, motor current flows through R2 and R18 (Fig. 1) across which a voltage proportional to the current occurs. This voltage signal is provided to a low pass filter (Fig. 5) consisting of R7 and R8 as well as C9 and C11.

C8 and R9 of U5: A create a voltage which is proportional to the difference between the incoming signal via the low pass filter and an internal bias voltage of the operational amplifier U5: A which is set by R20, R22 and C7. This portion of the circuit is referred to as a differentiator.

A Schmitt trigger circuit is provided by R10, Rll and R12 with C15 working with U5: B which converts the differential signals from the output of U5: A (at pin 1) and the internal bias voltage set by R20, R22 and C7 into two logic levels. This circuit buffers the logic signal and also has a hysteresis provided by Rll, R10 and filtering provided by R12 and C15.

The output of the Schmitt trigger is provided to a pulse conditioner comprising a mono-stable circuit based on U6: A which lengthens the period of the typically short pulses to eliminate multiple counting of noise near the pulse of interest.

Finally, the logic pulses at the output of U6: A are provided to the PULSE input of U2 (Fig. 2) for counting via D2. Thus the function of the pulse separator (all of Fig.

5) is clear from the prior paragraphs.

The micro controller is thus able to determine from a predetermined start position (eg fully to one or other of the end of travel or a start position represented by the desired position of the reflective element for example) a relative measurement of the element's location from the predetermined start position by using the pulse separator of Fig. 5. Since the micro controller also knows in which direction the motor is turning it can decrement or increment the relative measurement accordingly so as to maintain an accurate relative measurement. Since the counts being made are independent of speed and load on the motor they are useable for repeatably restoring one or more preferred locations even though the initial adjustment may have been made manually by the operator.

It is also possible to gauge the relative position of the mirror by counting the pulses required to park the mirror after a manual adjustment in which case the operation of parking the mirror is done with no pulse width modulation so that motor current is substantially constant and pulse counting is used to determine its relative position.

As previously discussed it is also important to be able to determine whether the element being actuated has reached its end of travel or alternatively stopped or become stuck unexpectedly intermediate the ends of its travel. Using either current drawn or the length of a pulse required to obtain a required back EMF it is possible to detect a stalled or overload condition of the motor.

If a current drawn measurement is made during normal operation of the motor and the current measured exceeds a predetermined level for more than a predetermined period the motor is determined to have stalled and in response to this the motor controller cuts-off current supply to the motor.

In the case of the motor being controlled based on back EMF measurements, the current supply pulse width on-time is also monitored and as the load on the motor increases the on-time extends. Once the on-time has exceeded a predetermined period the motor is determined to have stalled and in response to this the motor controller cuts-off current supply to the motor.

In a preferred embodiment motor supply current pulse on-time is controlled by the micro controller U2 (Fig. 2) and flows through R2 and R18 creating a voltage across them which is proportional to the current drawn by the motor. Any high frequency component of this signal is attenuated by R7 and R8 working in conjunction with C9 and C11 (Fig. 5). Signal IMOTORF is input to the micro controller U2 (Fig. 2) at pin 8 within which an A to D converter translates the analog voltage variations to a digital representation of the voltage and hence a digital representation of the current flowing through the motor. If a predetermined current limit is exceeded, the micro controller cuts-off current supply to the motor as it has determined that the motor has stalled.

Using the circuit and techniques described above, software installed in the micro controller can perform one or more of the following tasks: 'When the vehicle is parked as signified by a park indication by way of a switch means related to the vehicle ignition being off, gear lever position or some other arrangement, the external rear view mirror housing is folded-in to a park position When the vehicle is no longer parked the mirror housing is folded-out to a use position and the reflective element (eg a mirror) is restored to the position it held prior to the housing being folded-in. There is no deployed position and associated detent to locate this mirror head in this position with a mono-axis mirror. In this case, the mirror needs to be accurately returned to the position last used by the driver or another pre-stored position.

When the vehicle external rear view mirror is in a folded-out position the vehicle user can manually control the reflective element position The vehicle external rear view mirror assembly can be tested by an external computer device and/or preset to a factory configuration.

The mirror may have means for preventing backlash through the gear train that is used to rotate the mirror. This may comprise a clamping clutch arrangement that is released upon initial movement of the mirror. The control circuit can be programmed to re-engage any backlash prevention means that may be used.

As backlash will always exist no matter the quality of the mechanics of the apparatus, backlash take up can be implemented by applying full supply voltage to the motor in the required backlash direction. A reduced voltage may be used to reduce operating speed. It will then be necessary to ignore the expected start current peak and wait for the current to rise to a preset level which signifies the end of the backlash. The supply to the motor is then switched off. Alternatively, other means may be used to control motor operation to take up backlash, including operating the motor for a predetermined number of pulses.

Obviously, there is a need in relation to a mono-axis mirror to reduce any movement of the mirror head which might otherwise result from backlash within the gear drive train. One particular way in which this can be achieved is the use of a rotation inhibiting means such as a clutch or friction device located between the mirror head and the mounting bracket which has a force applied to it to prevent movement of the mirror head with respect to the bracket. With the drive arrangement associated with this type of mirror, it is preferable for the electric motor to also disengage and re-engage the rotation inhibiting arrangement. With such an arrangement, it maybe necessary to run the electric motor in the opposite direction for a brief period of time subsequent to mirror head motion to ensure re-engagement of the rotation inhibiting means.

When the micro controller operates the motor to move the mirror the motor first acts to disengage the rotation inhibiting means and then to subsequently rotate the mirror head. The duration required to disengage the rotation inhibiting means will generally be a fixed period or angle of mirror head rotation that is the same with each operation of the motor. Accordingly, this predetermined period can be allowed for within the operation of the motor and taken into account so that the mirror can be returned to the required position. In addition, the motor can then be run in a reverse direction for at another predetermined period to ensure proper re-engagement of the rotation inhibiting means.

The micro controller can also be arranged to perform a number of operations which are preferable so as to ensure reliable and easy use of the mirror assembly.

The vehicle user may manually control the position of the reflective surface if the mirror assembly is in an unparked condition. When a manual operation by the control switches is initiated, the signals from the switches are received by the micro controller and preceding the receipt by the motor of the required control signals, the motor will be operated to take up any backlash that may have developed.

This automatic take up of the possible backlash avoids the mechanism lurching and minimising any delay. The reflective element is then moved in the desired direction either at constant speed or at a speed proportional to the position of the user operated switch. If the operator switch is released prior to the take up of all of the mechanical backlash, the micro controller should continue to take up backlash until it is eliminated and then stop the motor.

When a park function of the mirror assembly is initiated, one of two preferable further functions are performed.

If a manual move of the reflective element has been performed since the last parking operation, backlash is taken up in the outward direction and the motor is then operated to move the reflective element to a fold-in position at full speed while pulses are counted. When the end stop is reached (current rise or other means of end stop detection) the micro controller stores the count in a non-volatile memory (preferably a EEPROM contained within the micro controller U2 (Fig. 2)).

In one example the starting point of the relative counting process can be the desired position of the reflective element.

If no manual move has occurred since the last park operation the micro controller simply moves the reflective element at full speed until it has detected a stop condition (counts or current rise for a period of time or alternatively applying current limiting to the motor for a predetermined period of time).

When the mirror assembly is to be unparked the motor is controlled to drive the mechanism to fold-out at maximum speed until the stored amount of pulses have been recounted. The motor is then stopped and the re-engagement of the rotation inhibiting means as previously described is performed.

With respect to the counting of motion pulses from the motor it may be necessary to apply a correction count to account for some unrecoverable backlash.

The correction may preferably add a 50 count when the mirror assembly unparks or reduces by a 50 count when the mirror assembly parks or some such other correction arrangement.

It will be appreciated by those skilled the art, that the invention is not restricted in its use to a particular application described and neither is the present invention restricted to its preferred embodiment with regards the particular elements and/or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention, therefore, the invention should be understood to include all such modifications within its scope.