Abstract:
A method for electronically controlling a bicycle gearshift comprising at least one derailleur is disclosed, comprising the sequential steps of:
   a) imparting a movement on the derailleur of the gearshift until the derailleur is in an intended position;   b) waiting for a predetermined time period,   c) performing a check whether the derailleur is in the intended position, within a possible predetermined tolerance,   d) in case said check has a negative outcome, imparting a movement on the derailleur of the gearshift until the derailleur is in the intended position.   
 
     A derailleur and an electronically servo-assisted bicycle gearshift comprising control electronics comprising modules adapted to carry out the method outlined above are also disclosed.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to a method for electronically controlling a bicycle gearshift, and to an electronically servo-assisted bicycle gearshift. 
       BACKGROUND 
       [0002]    A motion transmission system in a bicycle comprises a chain extending between toothed wheels associated with the axle of the pedal cranks and with the hub of the rear wheel. When there is more than one toothed wheel at at least one of axle of the pedal cranks and the hub of the rear wheel, and the motion transmission system is therefore provided with a gearshift, a front derailleur and/or a rear derailleur are provided for. In the case of an electronically servo-assisted gearshift, each derailleur comprises a chain guide element, also known as cage, movable to move the chain among the toothed wheels in order to change the gear ratio, and an electromechanical actuator to move the chain guide element. The actuator in turn typically comprises a motor, typically an electric motor, coupled with the chain guide element through a linkage such as an articulated parallelogram, a rack system or a worm screw system, as well as a sensor of the position, speed and/or acceleration of the rotor or of any moving part downstream of the rotor, down to the chain guide element itself. It is worthwhile noting that slightly different terminology from that used in this context is also in use. 
         [0003]    Control electronics changes the gear ratio automatically, for example based on one or more detected variables, such as the travel speed, the cadence of rotation of the pedal cranks, the torque applied to the pedal cranks, the slope of the travel terrain, the heart rate of the cyclist and similar, and/or based on commands manually input by the cyclist through suitable control members, for example levers and/or buttons. 
         [0004]    In order to drive the actuator, instead of assuming that the toothed wheels are equally axially spaced and therefore moving the chain guide element always by the same amount, the control electronics use a table of values containing, for each toothed wheel, the value that a variable of the derailleur must assume to position the chain in engagement with the toothed wheel. Such a value can be a differential value with respect to the adjacent toothed wheel, or it can be an absolute value with respect to a reference, for example with respect to a reference toothed wheel or to an end of stroke condition or to a condition of lack of excitation of the motor. 
         [0005]    From the point of view of magnitude, the command value of the actuator can for example be the distance travelled by a mobile point taken as a reference on the derailleur, the number of steps or revolutions that the motor should be made to perform, a length of excitation time of the motor, the value of a supply voltage of a motor having an excursion proportional to the voltage, furthermore it can be the value emitted by the sensor associated with the motor, a numerical value stored in a register and representative of one of the aforementioned quantities, etc. 
         [0006]    In particular, the motors of the actuators can be driven for a number of steps or for a length of excitation time or with a voltage that are appropriate for each upward or downward gearshifting and then automatically stopped, while the sensors are used to supply a feedback signal to the control electronics so that it can possibly take care of actuating the motors of the actuators again in case the intended position has not been reached, namely in case the aforementioned variable of the derailleur has not assumed the table value. This may for example be due to the fact that the resistant torque offered by the derailleur, which to a certain extent depends on how the cyclist is pedalling, was too high, greater than the maximum torque that can be delivered by the motors through the linkage. 
         [0007]    The values of said table of values are nominal values, set in the factory, which take the number of toothed wheels in the derailleur (front or rear) and the respective thicknesses and pitches into account. Typically, such nominal values provide that, in the absence of the driving signal of the actuator, namely with command value at zero, the chain is in engagement with the toothed wheel having the smallest diameter, although as can be seen from the aforementioned examples, this condition is not necessary. 
         [0008]    There are also some known gearshifts, for example from EP 1 426 284 A1 and from European patent application 11425204.2 not yet published at the priority date of the present application, wherein the nominal command values of the actuator are replaced in use by actual command values of the actuator, to take into account the variations in position of the toothed wheels, with respect to the nominal ones of a gearshift taken as a reference, due to various factors. 
         [0009]    In the present description reference will be broadly made to “command values of the actuator”, meaning the actual ones where present, or the nominal ones, referring to a reference gearshift, in case the actual ones are not present. 
         [0010]    More specifically, EP 1 426 284 A1 disclosed an electronically servo-assisted gearshift wherein a setting operating mode, an adjustment operating mode and a normal ride mode are implemented. In the setting mode, the chain is brought into alignment with a single preselected toothed wheel, preferably the one having the smallest diameter, and a biunique correspondence is set between the physical position of the actuator and the logic value associated with the gear ratio relative to the preselected toothed wheel, preferably zeroing a counter to the content of which the nominal values of the table are referred. In the adjustment mode, the chain is brought into engagement and alignment with a preselected toothed wheel and an adjustment variable (“offset”) of the logic value associated with the gear ratio relative to the preselected toothed wheel is set. During the normal ride mode, the actuator is moved into physical positions determined by the logic values associated with the toothed wheels as adjusted by the adjustment variables. In this way, the misalignments between the chain and one or more toothed wheels are compensated, caused for example by impacts or collisions or by small differences between the size and/or the position of a replaced toothed wheel and the replacement one. 
         [0011]    Moreover, European patent application 11425204.2 discloses in particular a method for electronically controlling a bicycle gearshift and a gearshift that implements it, comprising the steps of: 
         [0012]    a) detecting a first actual command value of an actuator such as to position a motion transmission chain in engagement with a first of at least three coaxial toothed wheels, and a second actual command value of the actuator such as to position the chain in engagement with a second of said toothed wheels, 
         [0013]    b) for each toothed wheel, determining a nominal command value of the actuator theoretically such as to position the chain in engagement with said toothed wheel, and 
         [0014]    c) computing an actual command value of said actuator at least for each of said toothed wheels other than the first and second toothed wheel, based on said nominal command values and said first and second actual command value. 
         [0015]    According to such a document, in this way it is possible to take into account not only the size differences of the components of the frame and the mounting tolerances of the gearshift, but also size differences inside the pack of toothed wheels with respect to the theoretical reference gearshift on which the nominal values are based. 
         [0016]    The Applicant has now perceived that, after the derailleur has reached the intended position at the end of its movement actuating a gearshifting—also when a feedback actuation of the derailleur is used and therefore the aforementioned movement includes movements correcting the resistant torque effect—, unintentional movements of the derailleur can follow, due to the elasticity of the linkage arranged between the motor of the actuator and the chain guide element, as well as due to vibrations due to the irregularity of the road surface. In the present description and in the attached claims, the derailleur is meant to be in intended position when the aforementioned variable of the derailleur has assumed the command value relative to the toothed wheel currently engaged. 
         [0017]    Such unintentional movements, even when they can be considered micro-displacements, can cause imprecisions in the actuation of subsequent gearshifting, particularly when the command values are expressed as differential values between adjacent toothed wheels and subsequent undesired movements can add to one another. Furthermore, such movements from the intended position can cause an imprecise engagement if not even the disengagement of the chain from the toothed wheel, and/or a greater wear of the mechanical parts. 
         [0018]    The technical problem at the basis of the invention is to counteract the undesired displacements of a derailleur of a bicycle gearshift. 
       SUMMARY 
       [0019]    In an aspect thereof, the invention concerns a method for electronically controlling a bicycle gearshift comprising at least one derailleur, comprising the sequential steps of: 
         [0020]    a) imparting a movement on the derailleur of the gearshift until the derailleur is in an intended position; 
         [0021]    b) waiting for a predetermined time period, 
         [0022]    c) performing a check whether the derailleur is in the intended position, within a possible predetermined tolerance, 
         [0023]    d) in case said check has a negative outcome, imparting a movement on the derailleur of the gearshift until the derailleur is in the intended position. Preferably, step a) of imparting a movement on the derailleur comprises actuating a motor of the derailleur and stopping it automatically when it is assumed that the derailleur is in an intended position, and carrying out a feedback control of the derailleur obtaining a feedback signal from at least one sensor, and optionally actuating the motor again in case the intended position has not been reached. 
         [0024]    Said step a) can be carried out as a consequence of a gearshifting request signal or to carry out a repositioning following a negative outcome of the check whether the position of the derailleur is the intended one, within a possible predetermined tolerance. In other words, even after step d) has been carried out, steps b), c), d) can be carried out. 
         [0025]    Preferably, between two successive executions of said step a) to carry out a respective gearshifting, said step b) of waiting and a step cl) of reading an actual position of the derailleur, as well as optionally said steps c) and d), are carried out cyclically, wherein said predetermined time period is comparatively long, preceded by at least one execution of said steps b), c), d), wherein said predetermined time period is comparatively short. 
         [0026]    Preferably, step b) of waiting for a predetermined time period comprises monitoring the passing of time with at least one timer. 
         [0027]    Typically, the intended position of the derailleur is a position that allows the positioning of a motion transmitting chain into engagement with a first of at least two coaxial toothed wheels, and it is evaluated based on a current value of a variable of the derailleur, wherein a predetermined value of the variable of the derailleur is provided for each toothed wheel associated with the derailleur. 
         [0028]    For the predetermined value of the variable of the derailleur for each toothed wheel, or command value, any numerical representation can be used that is representative of the condition of the derailleur in which the chain is in such a physical position as to engage on a specific toothed wheel. 
         [0029]    Preferably, the command values are represented with a numerical representation having a proportional scale. 
         [0030]    Preferably, step c) of checking is repeated a predetermined number of times irrespective of the outcome of each check, when said step a) is carried out to actuate a gearshifting. 
         [0031]    Preferably, said step d) is repeated at most a predetermined number of times before a second execution of step a) actuating a gearshifting consequent to a second gearshifting request signal. 
         [0032]    Each repetition of said step d) for the predetermined number of times can be carried out when said step c) of checking with a negative outcome is carried out after the comparatively short time period or when said step c) of checking with a negative outcome is carried out after the comparatively long time period. 
         [0033]    Preferably, if during said step b) of waiting there is a gearshifting request signal, the intended position is updated and the execution of step a) is returned to. 
         [0034]    In a second aspect thereof, the invention concerns an electronically servo-assisted bicycle gearshift, comprising: 
         [0035]    a chain and toothed wheels system for transmitting motion from the axle of the pedal cranks to a driving wheel of the bicycle, said motion transmission system comprising at least two toothed wheels that are coaxial along an axis selected from the axle of the pedal cranks and the axis of the driving wheel, 
         [0036]    at least one derailleur comprising a chain guide element and an actuator of the chain guide element to move the chain in engagement with a preselected toothed wheel of said at least two coaxial toothed wheels, and 
         [0037]    control electronics comprising modules adapted to carry out the method outlined above. 
         [0038]    Preferably, said actuator comprises a DC brush motor driven by a suitable number of “steps”, each corresponding to a fraction of a revolution, more preferably to one thirty-second of a revolution. 
         [0039]    In an aspect thereof, the invention concerns a derailleur comprising a chain guide element and an actuator of the chain guide element to move a chain in engagement with a preselected toothed wheel of at least two coaxial toothed wheels, and control electronics comprising modules adapted to carry out the method outlined above. 
         [0040]    In an aspect thereof, the invention concerns a bicycle comprising an electronically servo-assisted bicycle gearshift as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]    Further features and advantages of the present invention will become clearer from the following detailed description of some preferred embodiments thereof, made with reference to the attached drawings. In the drawings: 
           [0042]      FIG. 1  schematically illustrates a perspective view of a bicycle equipped with an electronically servo-assisted gearshift according to the present invention, 
           [0043]      FIG. 2  illustrates a block diagram of the electrical and electronic part of the electronically servo-assisted gearshift according to an embodiment of the present invention, 
           [0044]      FIG. 3  schematically illustrates a data structure used according to the present invention, 
           [0045]      FIG. 4  illustrates an examplary flow chart of the electronic control of the gearshift according to the invention, and 
           [0046]      FIGS. 5-10  are schematic time charts illustrating the operation of the electronic gearshift controlled according to the flow chart of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0047]    With reference to  FIG. 1 , a bicycle  1 , in particular a racing bicycle, includes a frame  2  formed in a known way of tubular elements defining a bearing structure  3  for a rear wheel  4  and a fork  5  for a front wheel  6 . Handlebars  41  having a tubular structure are operatively connected to the fork  5  and to the frame  2 . 
         [0048]    The frame  2 , at its lower portion, bears an axle of the pedal cranks or pedal units  7 , of the conventional type, to actuate the rear wheel  4  through an electronically servo-assisted gearshift according to the invention, indicated in general with reference numeral  8 . 
         [0049]    The gearshift  8  comprises a rear gearshift group  9  and a front gearshift group  10 . Rear gearshift group  9  includes a plurality of toothed wheels or sprockets  11  having different diameters and coaxial with the rear wheel  4 . Front gearshift group  10  includes a plurality of toothed wheels or crowns or gearwheels  12 , having different diameters and coaxial with the axle of the pedal cranks  7 . 
         [0050]    The toothed wheels  11  of the rear gearshift group  9  and the toothed wheels  12  of the front gearshift group  10  can be selectively engaged by a closed loop motion transmitting chain  13 , to provide the different gear ratios available, through the electronically servo-assisted gearshift  8 . 
         [0051]    The different gears ratios can be obtained by moving a chain guide element (cage) of a rear derailleur  14  of the rear gearshift group  9  and/or a chain guide element (cage) of a front derailleur  15  of the front gearshift group  10 . 
         [0052]    In the respective derailleur  14 ,  15 , the rear chain guide element and the front chain guide element are moved by a respective electric motor  16 ,  17  ( FIG. 2 ), typically equipped with a reducer and associated with the chain guide element through an articulated parallelogram linkage. Alternatively, it is possible to use other types of motor or other types of actuator or linkage that are well known in the art, for example a rack or worm screw system, for example the one described in U.S. Pat. No. 6,679,797, incorporated herein by reference. 
         [0053]    The derailleurs  14 ,  15  typically comprise a respective position, speed and/or acceleration sensor  18 ,  19  ( FIG. 2 ). The sensor can be associated with the rotor of the motor  16 ,  17 , or with any mobile part “downstream” of the rotor, down to the chain guide element itself. 
         [0054]    The details of the construction of the derailleurs  14 ,  15  are not illustrated here since the present invention lies outside their specific construction. For more details, reference shall be made for example to the description of the patent applications and patents quoted above. 
         [0055]      FIG. 2  represents, in the form of a block diagram, the electrical and electronic part of the electronically servo-assisted gearshift according to an embodiment of the present invention. 
         [0056]    An electronic power unit or board  30 , equipped with a battery, supplies the electrical power to the motors  16 ,  17  and to the sensors  18 ,  19  of the derailleurs  14 ,  15 , to an electronic board referred to hereinbelow as interface unit or board  32 , and possibly to an electronic board referred to hereinbelow as sensor board or unit  34 . The battery is preferably of the rechargeable type and the rear derailleur  14  can include, in a per se known way, a dynamo-electric unit to recharge the battery. In  FIG. 2 , the power supply lines are not shown for the sake of simplicity. 
         [0057]    The electronic power board  30 , the interface unit  32  and the sensor unit  34  as a whole form an electronic controller or control electronics  40  of the electronically servo-assisted gearshift  8 . Alternatively, there can be a single electronic board or a different number of electronic boards. 
         [0058]    In the present description and in the attached claims, therefore, under electronic controller or control electronics  40  a logic unit shall be meant, which can however be formed of many physical units, in particular of one or more distributed microprocessors that can be contained for example in the electronic power board  30 , in the interface unit  32  and/or in the sensor unit  34 . 
         [0059]    The electronic power board  30  is housed for example in one of the tubes of the handlebars  41  or in one of the tubes of the frame  2 , for example at a support for a drinking bottle (not illustrated). The interface unit  32  is housed for example in one of the tubes of the handlebars  41  or in a grippable device or manual control device  42  mounted on it. The sensor board  34  is housed for example in one of the tubes of the frame  2 , near to the sensors associated therewith. 
         [0060]    The transfer of power, data and information among the various components is carried out through electric cables, advantageously housed inside the tubes of the frame  2 . The transfer of data and information signals can also take place in wireless mode, for example with Bluetooth protocol. 
         [0061]    During travel, the rear and front derailleurs  14 ,  15  are controlled by the electronic controller  40  based on upward or downward gearshifting request signals entered by manual control devices  42 , or semi-automatically or automatically by the electronic controller  40  itself. The manual control devices  42  can for example comprise levers or buttons suitable for switching the state of switches  36  connected or arranged on the interface unit  32 . The switches  36  can be directly actuatable or each one through a lever, or two buttons can be actuatable by a swing lever. 
         [0062]    Typically, there are levers or buttons ( FIG. 2 ) arranged on or near a handgrip of the handlebars  41  for the upward and downward gearshifting signals, respectively, of the rear gearshift group  9 , and levers or buttons arranged on or near the other handgrip of the handlebars  41  for the upward or downward gearshifting signals of the front gearshift group  10 . There are typically also levers or buttons for actuating one or more of the switches  36 , which are intended to control auxiliary functions, like for example the selection of an operating mode. 
         [0063]    In the gearshift  8 , the electronic controller  40  and more specifically the sensor unit  34  preferably also has one or more sensors  38  of travel parameters, such as the travel speed, the speed of rotation of the pedal cranks, the slope of the travel terrain, the heart rate of the cyclist and the like, associated therewith. 
         [0064]    In an embodiment, the electronic controller  40 , in order to actuate a gearshifting, actuates the motor  16 ,  17  and, based on the signal of the sensor  18 ,  19 , stops the motor  16 ,  17  when the desired gear ratio has been reached, namely when the chain guide element of the derailleur  14  or  15  has reached such a position as to allow the correct engagement of the chain  13  with the desired toothed wheel  11  or  12 , for example the wheel adjacent (having a larger or smaller diameter, respectively) to the one at which it was located when the (upward or downward, respectively) gearshifting command was generated through the manual control device  42  and the switch  36 , and/or by the electronic control unit  40 , based on the output of the sensors of the travel parameters  38 . The desired toothed wheel may not be adjacent to the starting toothed wheel, in the case of multiple gearshifting. 
         [0065]    In an alternative embodiment, the motors  16 ,  17  are driven for a time or for a number of steps or with a voltage value that are appropriate for each upward or downward gearshifting and then automatically stopped, while the sensors  18 ,  19  are only optionally present and in such a case are used to provide a feedback signal to the electronic controller  40  so that it can possibly take care of actuating the motors  16 ,  17  again in case the physical position that brings the chain  13  in engagement with the desired toothed wheel  11  or  12  has not been reached. This may for example be due to the fact that the resisting torque offered by the derailleur  14 ,  15 , which to a certain extent depends on how the cyclist is pedalling, was too high, greater than the maximum torque which can be delivered by the motors through the linkage. 
         [0066]    The motors  16 ,  17  can for example be stepper motors. Preferably, the motors  16 ,  17  are DC brush motors that are driven by a suitable number of “steps”, each corresponding to a fraction of a revolution, more preferably to one thirty-second of a revolution. The choice of such a fraction is advantageous for processing, since it is an integer multiple of  2 . 
         [0067]    The electronic controller  40  further comprises memory means  44 , based on which the electronic controller  40  determines the command values of the actuators such as to position the chain  13  in engagement with the toothed wheels  11 ,  12  desired on each occasion. 
         [0068]    The electronic controller  40  can implement a rear counter  46  and a front counter  48 . The counters  46 ,  48  can for example each be made of a register or of a variable stored in a memory cell. The electronic controller  40 , in the normal ride operating mode of the gearshift  8 , drives the derailleurs  14 ,  15  and keeps track of their current position by increasing or decreasing the counters  46 ,  48 , for example by one unit for each step imposed on the motor  16 ,  17  and/or based on the reading of the sensors  18 ,  19 . The counters  46 ,  48 , where provided for, express the current position of the derailleurs  14 ,  15  in the same unit of measurement as the command values stored in the memory means  44 . In this case, the counters  46 ,  48  can also act as sensors  18 ,  19 . 
         [0069]    The memory means  44  of the command values and the counters  46 ,  48  are shown as stand-alone parts of the electronic controller  40 , but they can be physically implemented in one or more of the memory devices present in the electronic boards  30 ,  32 ,  34 . 
         [0070]    In simpler bicycles, there can be only the rear gearshift group  9  or only the front gearshift group  10 , with the simplifications to the above that will be manifest to those skilled in the art. 
         [0071]    For easiness of explanation, hereinafter the rear gearshift group is referred to in particular. What follows is applicable, alternatively or additionally, to the front gearshift group, mutatis mutandis. 
         [0072]      FIG. 3  illustrates a data structure, stored in a memory area of the electronic controller  40 , like for example the aforementioned memory  44 , or in any case accessible thereto, wherein the command values Q i  of the actuator are stored in the form of a table  60 , with i being an integer number between 1 and N, for each toothed wheel or sprocket of a gearshift group. In the example case of a rear gearshift group containing eleven sprockets, the table comprises the command values from Q 1  to Q 11 . 
         [0073]    More specifically, the command value Q 1  represents, in a suitable measurement unit, the theoretical condition of the gearshift in which the chain  13  is in such a physical position as to engage on the sprocket  11  having the smallest diameter of the rear gearshift group  9 ; the command value Q 2  represents the condition, in the same measurement unit, in which the chain  13  is in such a physical position as to engage on the sprocket  11  adjacent thereto of the rear gearshift group  9 ; etc. up to the command value Q N —in the case illustrated Q 11 —which represents the condition, again in the same measurement unit, in which the chain  13  is in such a physical position as to engage on the sprocket  11  having the maximum diameter of the rear gearshift group  9 . 
         [0074]    The command values Q i  are preferably stored in the factory as values, called “nominal values”, referring to a standard or reference gearshift and possibly adjusted later, as values called “actual values”, to take misalignments between the chain  13  and one or more toothed wheels  11  into account, caused for example by impacts or collisions, or by small differences between the size and/or position of a replaced toothed wheel and the replacement one, as well as size differences of the components of the frame and the mounting tolerances of the gearshift, and by size differences inside the pack of toothed wheels with respect to the theoretical reference gearshift on which the nominal values are based. 
         [0075]    For example, each command value Q i  can be expressed as a value, possibly stored in the counter  46 , that the output of the sensor  18  must take up or as a value of a driving quantity of the motor  16 . 
         [0076]    For example, when the actuator comprises a stepper motor or a motor driven by fractions of a revolution as stated above, each command value Q i  can be expressed as the number of steps necessary to reach the condition of engagement with the i-th toothed wheel, starting from a reference position, corresponding for example to an end of stroke position or to the condition of lack of excitation of the motor  16  or to the condition of engagement with the toothed wheel having the smallest diameter. 
         [0077]    Each command value Q i  can also be expressed as the position of a specific point of the actuator or of the chain guide element, or as the distance of such a point, for example in millimetres, from a reference plane, for example taken on the bicycle, or in the condition of engagement with a reference toothed wheel. Furthermore, each command value Q i  can be expressed as the value of a power supply voltage of a motor  16  that causes a movement of the chain  13  proportional thereto, or in other ways, according to the type of actuator, as will be understood by those skilled in the art. 
         [0078]    Each command value Q i  can also be expressed in a differential manner, with reference to the adjacent toothed wheel, for example as the distance to be travelled, as the number of steps to be carried out, as the actuation time of the actuator, etc., according to the type of actuator, as will be understood by those skilled in the art. In this case, for each toothed wheel there will more precisely be a command value starting from the toothed wheel of immediately smaller diameter and a command value starting from the toothed wheel of immediately greater diameter, the changes to be made to what follows being within the skills of those skilled in the art. In an even more elaborate embodiment, there can be, for each toothed wheel and for each direction from which it is reached, a command value based on which to bring the chain temporarily for the engagement operation, and a command value based on which to bring the chain upon successful engagement. 
         [0079]    For the sake of easiness, reference shall be made to the case of command values Q i  expressed in a proportional measurement unit. 
         [0080]    Table  60  of  FIG. 3  also indicates a field i having values from 1 to N, in this particular case from 1 to 11. However, it should be understood that in a practical implementation, this field can be absent should the command values Q i  be stored sorted by diameter of the corresponding toothed wheel. Indeed, table  60  will be looked at, as better described hereinafter, each time obtaining a specific value Q i  based on the value of a current index i=1 . . . N. If the values Q i  are sorted, it will therefore be sufficient to look at the i-th value in the table  60 . 
         [0081]    Although in  FIG. 2  a single memory  44  is shown schematically, it should be understood that in practice there can be various storage devices. Preferably, the nominal command values Q i  are stored in an EEPROM memory or in a read only memory, for example a ROM, while the actual command values are stored in the same or in another EEPROM memory or in a read and write memory. 
         [0082]    Although a single table of command values is shown for greater clarity, both the nominal command values and the actual command values could also be stored in a common data structure or in distinct tables. 
         [0083]    In the present description reference is made to the command values in use, be they the nominal one or the actual ones, and reference is made to a single table of values  60 , irrespective of the fact that there can be two distinct tables for the nominal values and for the actual values. 
         [0084]    During a normal ride operating mode, should it be necessary to carry out a change of gear ratio bringing the chain  13  to engage the i-th toothed wheel, the electronic control unit reads from table  60  the command value Q i  associated with the i-th toothed wheel and drives the actuator and in particular the motor  16  as a consequence. 
         [0085]    In particular, in case the motor  16  is of the stepper type or actuated by “steps” each one equivalent to a fraction of a revolution as stated above, it is driven to move by one step at a time or by a certain number of steps at a time. 
         [0086]    Preferably, the origin of the reference system for the command values Q i  is selected at the A-th first toothed wheel, namely Q 1 =0. 
         [0087]    It should be understood that the command values can increase for toothed wheels of increasing diameter, or increase for toothed wheels of decreasing diameter. 
         [0088]    The control method according to the invention, described in detail hereinafter, can be implemented in a controller marketed together with a derailleur, but independently of the toothed wheels, the chain and the other components of a gearshift. 
         [0089]    The electronic control of the gearshift according to the invention will now be described with reference to  FIG. 4 , which illustrates an example flow chart of an embodiment thereof, and to  FIGS. 5-10 , which are schematic time charts illustrative of the operation of the electronic gearshift  8  controlled according to the flow chart of  FIG. 4 . 
         [0090]    In a block  101 , a check counter NC is initialized to a maximum number of controls or checks MAXC that the position of the derailleur is an intended position, namely the default one of the gearshift or the one in accordance with the last gearshifting performed. The maximum number of checks MAXC is selected, together with the value of a time period MAX 2  between two successive checks described hereinafter with reference to block  118 , experimentally, as a function of the speed and the total unintentional movement time observed in the gearshift model. Such a time and speed are a function of the elasticity of the linkage arranged between actuator and chain guide element. The value MAXC can be selected, for example, of a few tens. 
         [0091]    More specifically, the intended position is the one in which the preselected variable of the derailleur as described above takes up the predetermined value Qi of table  60 , which allows the positioning of motion transmitting chain  13  in engagement with the intended i-th toothed wheel  11 ,  12 , which for example will be the one having the smallest diameter (i=1 according to table  60 ) upon switching on, the one (of index i=i′+1 according to table  60 ) immediately subsequent to the toothed wheel  11  previously engaged (of index i′ according to table  60 ) after performing a single upward gearshifting, the one (of index i=i&#39;−1 according to the table  60 ) immediately preceding the toothed wheel  11  previously engaged after performing a single downward gearshifting, or a toothed wheel not immediately subsequent or preceding in the case of multiple upward or downward gearshifting, respectively. 
         [0092]    In a subsequent block  102 , a repositioning operations counter NR is initialized to a maximum number of repositioning operations MAXR of the derailleur to be carried out when it is not in the intended position. The maximum number of repositioning operations MAXR is selected based on the conflicting requirements of maintaining a position of the derailleur that is as accurate as possible on the one hand and, on the other hand, of not placing excessive strain on the mechanical parts, preserving electrical energy and not overloading the control electronics  40 . The value MAXR can be selected, for example, as equal to a few units. A number of repositioning operations too high could lead to excessive strain on the mechanical parts of the derailleur, besides too much consumption of the battery: after a few repositioning operations it is preferable to give up repositioning and wait for the cyclist to realize that the motion transmission system is not running properly and therefore to change gear ratio. 
         [0093]    The maximum number of repositioning operations MAXR is preferably less than the maximum number of checks MAXC. 
         [0094]    In a subsequent block  103 , a counter or first timer T 1  is initialized to a value MAX 1  that represents a first time period after which it is wished to perform a check that the position of the derailleur is the intended position, between one gearshifting and the other. 
         [0095]    As discussed in the introductory part of the present disclosure, the position of the derailleur may not have remained the intended one—reached during the movement imparted to the derailleur—due to undesired movements, which may even be microscopic. 
         [0096]    The first time period MAX 1  is comparatively long with respect to the second time period MAX 2  described hereinafter with reference to block  118 , for which reason sometimes in the rest of the present disclosure and in the attached claims the expressions comparatively long timer T 1 , comparatively long time period MAX 1 , comparatively short timer T 2 , comparatively short time period MAX 2  will be used. 
         [0097]    The first time period MAX 1  can be selected, for example, as a few tens of seconds. The first time period MAX 1  can be expressed in a suitable scale. 
         [0098]    In a subsequent block  104 , it is checked whether there is a gearshifting request signal. This signal can be generated by the cyclist or automatically by the control electronics  40  based on the outputs of the sensors  38  of the travel parameters as stated above. 
         [0099]    In case the check of block  104  gives a negative outcome, in a block  105  it is checked whether the first time period MAX 1  has elapsed, namely—in the embodiment shown—whether the first timer T 1  has finished the countdown and therefore T 1 =0. 
         [0100]    In case the first time period MAX 1  has not elapsed, output NO of block  105 , in a block  106  the value of the timer T 1  is decreased, typically by a unit of the same scale as the first time period MAX 1 , and performing of block  104  of checking whether there is a gearshifting request signal is returned to. 
         [0101]    If there is no gearshifting request signal for the duration of the first time period MAX 1 , at the end of such a time period MAX 1  the first timer T 1  will have finished the countdown and therefore T 1 =0 will be true, output YES from block  105 . 
         [0102]    In this case, in a block  107  the value of the check counter NC is set to zero. The zero value is set on the check counter NC for convenience in the block diagram, but as will be immediately seen, even with such a value of the check counter NC a check of the position is actually performed. Alternatively, it is possible to use a separate flag to indicate that the comparatively slow time period MAX 1  has elapsed without gearshifting requests and actuations. After block  107 , in a block  108  the actual position of the derailleur is obtained, reading the output of the respective sensor  18 ,  19 . 
         [0103]    In a subsequent block  109  it is checked whether the repositioning operations counter NR—which is decreased in a block  113  described hereinafter—is now at zero. 
         [0104]    In the negative case, like at the first execution of block  109 , in a subsequent block  110  it is checked whether the actual position of the derailleur corresponds to the intended one, apart from a suitably predetermined tolerance, which however can also be zero. 
         [0105]    In the affirmative case, no corrective action is necessary and the value of the repositioning operations counter NR is brought back—or reconfirmed, in case it was not decreased—to the maximum number of repositioning operations MAXR in a block  111 . 
         [0106]    In case the actual position of the derailleur does not correspond to the intended one and it is not within the possible predetermined tolerance around such an intended position—output NO from block  110 —, it is provided in a block  112  to actuate the motor  16 ,  17  of the actuator until the derailleur is in the intended position, possibly exploiting the output of the sensors  18 ,  19  as feedback signal as described above. 
         [0107]    As soon as the derailleur is in the intended position, in a block  113  the value of the repositioning operations counter NR is decreased by one unit. It should be noted that in the absence of the feedback signal from the sensors  18 ,  19 , it is assumed at the end of the block  112  that the derailleur is in the intended position. 
         [0108]    Irrespective of the outcome of the check of block  110  whether the actual position of the derailleur corresponds to the intended one apart from the predetermined tolerance, after block  111  or blocks  112 ,  113 , respectively, it is checked in a block  114  whether the check counter NC—which can be decreased in a block  122  described hereafter—is now at zero. 
         [0109]    It should be noted that the same block  114  is reached in case the check of block  110  whether the actual position of the derailleur corresponds to the intended one apart from the predetermined tolerance is not carried out due to the repositioning operations counter NR running out (output YES of block  109 ). 
         [0110]    In case the check counter NC is at zero, as occurs for example in the case now examined in which no gearshifting request command has been received during a time period MAX 1 , since the check counter NC has been set to zero in block  107 , execution of block  103  is returned to, in which the comparatively long timer T 1  is reset to the maximum value MAX 1 , and then to block  104  of checking whether there is a gearshifting request signal. 
         [0111]    Before proceeding with the description of the block diagram following other assumptions the behaviour in the assumption followed of not receiving any command for a comparatively long time period MAX 1  is summarized, with reference to the schematic time charts of  FIGS. 5-7 . It is assumed in such time charts that the maximum number of checks is MAXC=3 and that the maximum number of repositioning operations is MAXR=2. 
         [0112]      FIG. 5  shows the case in which, after a comparatively long time period MAX 1 , the reading of the position (block  108 ) is within tolerance (output YES from block  110 ). Then another comparatively long time period MAX 1  is waited and, thereafter, another reading of the position is carried out, which is assumed to again be within tolerance. Since the check counter NC is always brought back to the zero dummy value, the situation put forward can repeat indefinitely. 
         [0113]      FIG. 6  shows the case in which, after a comparatively long time period MAX 1 , the reading of the position (block  108 ) is not within tolerance (output NO from block  110 ). A first repositioning is thus carried out (block  112 ), decreasing (block  113 ) by one unit the value of the repositioning operations counter NR, then another comparatively long time period MAX 1  is waited and, thereafter, another reading of the position is carried out, which this time is assumed to be within tolerance. The repositioning operations counter NR is then brought back to the maximum value MAXR (block  111 ). As above, since the check counter NC is also brought back to the zero dummy value (block  107 ), the situation put forward can repeat indefinitely. 
         [0114]    Finally,  FIG. 7  shows the case in which, after a comparatively long time period MAX 1 , the reading of the position (block  108 ) is not within tolerance (output NO from block  110 ). A first repositioning is thus carried out (block  112 ), decreasing by one unit the value of the repositioning operations counter NR (block  113 ), then another comparatively long time period MAX 1  is waited and, thereafter, another reading of the position is carried out, which once again has a negative outcome. Then a second repositioning is carried out, decreasing by one unit the value of the repositioning operations counter NR. Having assumed that the maximum number of repositioning operations MAXR is  2 —or after a number MAXR of behaviours as described—, the repositioning operations counter NR thus reaches zero. After having waited another comparatively long time period MAX 1 , another reading of the position is carried out (block  108 ), but it is not checked whether it is within tolerance (output YES from block  109 ), and in any case repositioning operations are not carried out. Since the check counter NC is brought back to the zero dummy value after every comparatively long time period MAX 1 , this last situation can repeat indefinitely: the derailleur stays in the unintended position, until the subsequent gearshifting, even if its position is checked with frequency MAX 1 . 
         [0115]    Indeed, as stated above after the maximum number of repositioning operations MAXR it is not considered suitable to move the derailleur  15  further so as not to stress too much the mechanics and not to consume too much power, preferring to wait for an intervention by the cyclist. Therefore, the check of whether the actual position is within tolerance (block  110 ) is also omitted. Vice-versa, the actual position of the derailleur is read in any case in block  108 , to keep track of it and therefore have a precise starting point and be able to carry out corrections as needed to the command values read in table  60 , especially in the case of a derailleur driven in a differential manner. 
         [0116]    In the case of non-differential command values of the derailleur  15 , keeping track of the actual position of the derailleur  15  can be avoided. In this case, blocks  108  and  109  could also have their positions inverted—and the relative outputs consequently adjusted—, therefore avoiding the reading of the actual position if the number of repositioning attempts NR has run out. 
         [0117]    Vice-versa, after reading the actual position the check of whether the actual position is within the tolerance can in any case be carried out, namely by moving the check whether the number of repositioning attempts NR has run out (block  109 ) to the output NO of block  110  of checking whether the position is within tolerance, just before the repositioning block  112 . 
         [0118]    It is also possible for example to also implement a negative check counter and a possible alarm signal to the cyclist once a maximum value thereof has been passed. Indeed, such a situation may even not be particularly critical (position just outside of the tolerance), but it could require a revision of the mechanics of the gearshift or of the command values of the table  60 . 
         [0119]    Turning back to the block diagram of  FIG. 4 , in case there is a gearshifting request signal during the elapsing of a comparatively long time period MAX 1 —output YES from block  104 —, in blocks  115  and  116  it is first provided to return—or reconfirm, in case they were not decreased—the check counter NC and the repositioning operations counter NR to the respective maximum value MAXC and MAXR allowed. 
         [0120]    Then, in a block  117  the motor  16 ,  17  of the actuator is actuated until the derailleur is in the intended position—which is a new intended position, at another toothed wheel—, possibly exploiting the output of the sensors  18 ,  19  as feedback signal as described above. 
         [0121]    As soon as the derailleur is in the intended position, in a block  118  a counter or second timer T 2  is initialized at a value MAX 2  that represents a second time period after which it is wished to carry out a check that the position of the derailleur is the intended position. Also in this case, the position of the derailleur may not have remained the intended one—reached during the movement imparted on the derailleur executing the gearshifting (block  117 )—due to undesired movements, which may even be microscopic, caused as stated above by the elasticity of the linkage of the derailleur  15  and/or by vibrations due to irregularity of the road surface. 
         [0122]    It should be noted that in the absence of the feedback signal from the sensors  18 ,  19 , it is assumed at the end of block  117  that the derailleur is in the intended position. 
         [0123]    As stated above, the second time period MAX 2  is comparatively short, since the Applicant has perceived that immediately after a gearshifting it is more likely that undesired microdisplacements of the derailleur occur. 
         [0124]    The second time period MAX 2  can be selected, for example, as a few tenths of a second. The second time period MAX 2  can be expressed in a suitable scale, preferably in the same scale as the first time period MAX 1 . 
         [0125]    In a subsequent block  119 , it is checked whether there is a (second) gearshifting request signal. 
         [0126]    In case the check of block  119  gives a negative outcome, in a block  120  it is checked whether the second time period MAX 2  has elapsed, namely—in the embodiment shown—whether the second timer T 2  has finished the countdown and therefore T 2 =0. 
         [0127]    In case the second time period MAX 2  has not elapsed, output NO of block  120 , in a block  121  the value of the timer T 2  is decreased, typically by one unit of the same scale of the second time period MAX 2 , and the execution of block  119  of checking whether there is a (second) gearshifting request signal is returned to. 
         [0128]    If the (second) gearshifting request signal is not present for the duration of the second time period MAX 2 , at the end of such a time period MAX 2  the second timer T 2  will have finished the countdown and therefore T 2 =0 will be true, output YES from block  120 . 
         [0129]    In this case, in a block  122  the value of the check counter NC is decreased by one unit and then in a block  123  it is checked whether the check counter NC is now at zero. 
         [0130]    In the negative case, like at the first execution of block  123 , one proceeds with execution from block  108  described above, carrying out a reading of the position of the derailleur, a check whether the position is within tolerance and a possible repositioning, then returning to executing block  114  of checking whether the check counter NC is now at zero, which will necessarily give a negative outcome. There is thus cyclical return to executing block  118  and therefore to waiting again for a time period MAX 2 , to the decrease of the check counter NC (block  122 ) and to the possible check of the position and possible repositioning, until the check counter NC reaches the zero value. In this cyclical repetition, the possible check of the position and possible repositioning of step  112  are carried out only until the repositioning operations counter NR reaches the zero value. 
         [0131]    When the check counter NC reaches the zero value, output YES from block  123 , the execution of block  103  is returned to. 
         [0132]    With the execution of blocks  118 - 123  now described a number NC of checks of the position are therefore carried out, at a strict frequency MAX 2 , possibly carrying out a maximum number of repositioning operations MAXR. 
         [0133]    In case the check of block  119  gives a positive outcome, and therefore a (second) gearshifting request signal intervenes during one of the NC position checks at frequency MAX 2 , in a block  124  the first counter T 1  is brought back to the maximum value MAX 1  and then the execution of blocks  115 - 118  is returned to. Therefore, in particular the new gearshifting is actuated by bringing the derailleur into the (new) intended position, and all of the counters and timers are brought to the maximum, like at the start. 
         [0134]    It is worthwhile emphasizing that, irrespective of the outcome of the checks following positioning executing a gearshifting (block  117 ) or following repositioning due to a position found to be outside of tolerance (block  112 ), a reading of the position is always carried out at least at each comparatively long time period MAX 1 . 
         [0135]    Moreover, a predetermined number MAXC of checks are always carried out at each comparatively short time period MAX 2  following positioning executing a gearshifting (block  117 ), irrespective of the outcome of the checks themselves. 
         [0136]    The behaviour in the followed assumption of receiving a gearshifting request signal will now be summarized, with reference to the schematic time charts of  FIGS. 8-10 . Analogously to  FIGS. 5-7  described above, it is assumed in such time charts that the maximum number of checks is MAXC=3 and that the maximum number of repositioning operations is MAXR=2. 
         [0137]      FIG. 8  shows the case in which, after a comparatively short time period MAX 2  after actuating the gearshifting (block  117 ), the reading of the position (block  108 ) is within tolerance (output YES from block  110 ). Another comparatively short time period MAX 2  is then waited and, thereafter, another reading of the position is carried out, which is assumed to be again within tolerance. Once again, for a third time a comparatively short time period MAX 2  is waited and, since each time the value of the check counter NC is decreased by one unit (block  122 ) and since the maximum number MAXC of checks is  3  in the assumed case, the check counter NC then reaches zero. Then one moves on to waiting for a comparatively long time period MAX 1 , after which another reading of the position is carried out (block  108 ), with checking whether it is within tolerance, assumed to be positive (output YES from block  110 ). 
         [0138]    As noted above, since the check counter NC is brought back to the zero dummy value (block  107 ) if gearshifting requests do not occur during the comparatively long time period MAX 1 , such reading of the position (block  108 ) with checking whether it is within tolerance can be repeated indefinitely. 
         [0139]    If at a certain point in time the position is not within tolerance (output NO from block  110 ), as shown, a repositioning will be carried out (block  112 ) with related decrease (block  113 ) of the repositioning operations counter NR. Since such a repositioning operations counter NR is brought back to the maximum value only after a position reading within tolerance (block  111 ) or after a gearshifting request signal (block  116 ), at most a number MAXR of repositioning operations can be carried out at time periods MAX 1 . 
         [0140]      FIG. 9  shows the case in which, after a comparatively short time period MAX 2  after actuating the gearshifting (block  117 ), the reading of the position (block  108 ) is within tolerance (output YES from block  110 ). Another comparatively short time period MAX 2  is then waited and, thereafter, another reading of the position is carried out, which this time is assumed to be outside of tolerance (output NO from block  110 ). 
         [0141]    A first repositioning is then carried out (block  112 ), decreasing (block  113 ) the value of the repositioning operations counter NR by one unit, then another comparatively short time period MAX 2  is waited. 
         [0142]    Since the number of checks NC has now reached zero, there is cyclical repetition of the waiting for a comparatively long time period MAX 1 , of carrying out another reading of the position (block  108 ), and of checking whether it is within tolerance (block  109 ). If the position is not within tolerance (output NO from block  110 ), as shown, a repositioning will be carried out (block  112 ) with related further decrease (block  113 ) of the repositioning operations counter NR. Since such a repositioning operations counter NR is at this point at zero in the case of maximum number of repositioning operations MAXR=2, at the next reading of the position it is not checked whether it is within tolerance and in any case the derailleur is not repositioned. 
         [0143]    Finally,  FIG. 10  shows the case in which, after a comparatively short time period MAX 2  after actuating the gearshifting (block  117 ), the reading of the position (block  108 ) is not within tolerance (output NO from block  110 ). A first repositioning is then carried out (block  112 ), decreasing (block  113 ) the value of the repositioning operations counter NR by one unit, then another comparatively short time period MAX 2  is waited and, thereafter, a second reading of the position is carried out, which is assumed to again not be within tolerance (output NO from block  110 ). A second repositioning is then carried out (block  112 ), decreasing (block  113 ) the value of the repositioning operations counter NR by one unit. Then another comparatively short time period MAX 2  is waited and, thereafter, since the number of checks NC has now reached zero, there is the cyclical repetition of waiting for a comparatively long time period MAX 1  and of carrying out another reading of the position; since the repositioning operations counter NR is however at this point at zero (output NO from block  109 ), the check whether the position is within tolerance (block  110 ) and the possible repositioning are not carried out, however. In any case, reference is made to what has been noted earlier on the order in which the steps  109  and  110  can be carried out. 
         [0144]    In an alternative embodiment, just one or other of the check counter NC and the repositioning operations counter NR could be used, although with less degrees of freedom and/or carrying out a single check whether the position is within tolerance or a single repositioning. 
         [0145]    It is also manifest that instead of using countdown counters it is possible to use incremental counters and/or that instead of using checks of the various counters on the value 0 it is possible to use checks on the value 1, by suitably changing the value of the corresponding maximum. 
         [0146]    Moreover, it is manifest that it is possible to use timers operating according to a clock signal instead of according to the decrements set in blocks  106  and  121 , the changes to the block diagram being within the capabilities of one skilled in the art. 
         [0147]    In case the motor  16 ,  17  of the derailleur is of the stepper type or actuated by “steps” each one equivalent to a fraction of a revolution as stated above, it can be driven to move a comparatively large number of steps at a time for positioning to execute a gearshifting (block  117 ) and one step at a time or a comparatively small number of steps at a time for repositioning when position is found to be outside tolerance (block  112 ), during which the total movement is typically less than the distance between two toothed wheels. 
         [0148]    The method outlined above can also be used in the case of automatic or semi-automatic operation of the bicycle gearshift, wherein the control electronics  40  establish—based on the outputs of the sensors  38  of the travel parameters—such as the travel speed, the rotation speed of the pedal cranks, the slope of the terrain, the heart rate of the cyclist and similar—when it is suitable to change gear ratio and automatically generate the signals requesting movement of the derailleur (automatic operation) or carry out a supervision/integration of the cyclist&#39;s requests, preventing them, bypassing them, delaying them and/or integrating them with automatically generated requests, or vice-versa proposing such requests to the cyclist that in any case has the option to bypass them (semi-automatic operation). 
         [0149]    The method outlined above can also be used in the case in which the cyclist sends command signals for a change in gear ratio and the electronic controller  40  takes care of transforming them into a gearshifting request signal of the rear derailleur and/or into a gearshifting request signal of the front derailleur. The method outlined above can be implemented in any component  30 ,  32 ,  34  of the electronic controller  40 , even in a manner distributed between two or three of such components  30 ,  32 ,  34 . 
         [0150]    The method outlined above can be implemented in a controller marketed together with a derailleur, but independently from the toothed wheels, from the chain and from the other components of a gearshift.