Abstract:
An actuator ( 1 M,  1 S) with a motor ( 12 ) and a motor controller ( 11 ) is configurable to operate as a master or a slave to another actuator which is coupled mechanically for driving a common load. For the case where the actuator ( 1 M) is set as the master, the motor controller ( 11 ) receives on an input terminal (Y 3 ) an external position control signal (pC), generates a motor control signal (sC) for controlling the motor ( 12 ) based on the position control signal (pC), and supplies the motor control signal (sC) to an output terminal (U 5 ) for controlling a slave. For the case where the actuator ( 1 S) is set as the slave, the motor controller ( 11 ) controls the motor ( 12 ) by supplying to the motor ( 12 ) the motor control signal (sC) received from the master. Controlling the actuators with a master improves workload balancing and reduces damages to transmission mechanics of the actuators.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/CH2011/000038 filed Mar. 2, 2011, the contents of all of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to an actuator comprising an electric motor and a motor controller. Specifically, the present invention relates to an actuator comprising an electric motor and a motor controller whereby the actuator is used to work cooperatively, i.e. in piggyback configuration, with another actuator which is coupled mechanically to the actuator for driving a common load. 
     BACKGROUND OF THE INVENTION 
     It is common practice to couple mechanically two or more actuators for driving a common load, i.e. to use two or more actuators in piggyback configuration or simply “piggybacked”. For example, the actuators are mechanically coupled directly through attachment to a common drive shaft or indirectly through connecting rods, levers, bars, other linkage assemblies, or parts of the load to be driven, e.g. a damper or a valve. Typically, and depending on the type and way of the mechanical coupling of the actuators to each other and/or the common load, the materials used for the mechanical coupling, and the distances between the individual actuators, etc., the load is not equally distributed among the piggybacked actuators, the force provided by their electrical motors is not optimally used and combined, and, worst of all, as a result, gear and transmission mechanisms of the actuators are damaged in the process. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an actuator which is suitable to work cooperatively with one or more other actuators which are coupled in piggyback configuration, for driving a common load, which actuator does not have at least some of the disadvantages of the prior art. 
     According to the present invention, these objects are achieved through the features of the independent claims. In addition, further advantageous embodiments follow from the dependent claims and the description. 
     According to the present invention, the above-mentioned objects are particularly achieved in that an actuator, comprising an electric motor and a motor controller, is configurable to operate as a master or a slave to another actuator which is coupled mechanically to the actuator for driving a common load. The motor controller is configured, for the case where the actuator is set as the master, to receive on an input terminal an external position control signal, to generate based on the position control signal (and the load) a motor control signal, e.g. a speed control signal or a torque control signal, to control the motor by supplying the motor control signal to the motor, and to control a slave by supplying the motor control signal to an output terminal. The motor controller is further configured, for the case where the actuator is set as the slave, to receive on the input terminal the motor control signal supplied by the master, and to control the motor by supplying the motor control signal from the master to the motor. Accordingly, two or more actuators which are coupled mechanically to drive a shared load follow the control signal of one common controller which is implemented on the actuator which is set up as the master and perceives a force feedback from the slave actuators through the mechanical coupling. Thus, inherent in the speed control signal provided by the master actuator to the slave actuator(s) is not only the speed at which the actuators are controlled to run, but also the momentum, or vice versa. Thereby, counter-productive work is avoided, the work load is balanced more equally among the piggybacked actuators, and more cooperative and efficient work load sharing is achieved and energy can be conserved, without damage to gear and transmission mechanics of the actuators, because the actuators drive their common load in the same direction and do not work against each other. 
     In a preferred embodiment, the motor controller is further configured to measure, at start-up time, voltage levels at the input terminal, and to set the actuator as a slave depending on the voltage levels measured at the input terminal. Automatic detection of a slave mode, based on voltage levels at an input terminal, makes it possible to set up an actuator as a slave simply through corresponding wiring of the slave actuator, provided the defined voltage levels are supplied by the master actuator or another external control system, for example. 
     In another preferred embodiment, the motor controller is further configured to reduce the impedance of the input terminal, for the case where the actuator is set as a slave. Furthermore, the motor controller is configured to detect at the output terminal a voltage reduction caused by a lowered impedance of another actuator connected to the output terminal, and to set the actuator as the master upon detecting the voltage reduction at the output terminal. Automatic detection of a master mode, based on an interrupt which is indicated by an abrupt voltage reduction caused by a lowered impedance level of a unit connected to the output terminal, makes it possible to set up an actuator as a master simply through corresponding wiring of the master actuator, provided the impedance level is lowered accordingly by one or more slave actuators or another external unit, for example. 
     In a preferred embodiment, the motor controller is further configured to set, at start-up time, a defined first voltage level at the output terminal, and to set a defined second voltage level at the output terminal, upon having been set as the master, the defined second voltage level being different from the first voltage level. Providing a different, e.g. reduced or increased, voltage level by the master actuator at the output terminal makes it possible for an actuator, which has its input terminal as a slave connected to the output terminal of the master actuator, to detect more reliably that it is indeed set up as a slave actuator connected to the master actuator. 
     In an embodiment, the motor controller is further configured, for the case where the actuator is set as a slave, to provide on the output terminal a position signal indicating a current actuator position. The position signal makes it possible to indicate to an external control system the actual and current positions of the actuator(s). 
     In an embodiment, the actuator further comprises one or more stored actuator parameters, e.g. a speed parameter and/or a torque parameter, and the motor controller is configured to generate the motor control signal based on the actuator parameters and the position control signal (and the load). Accordingly, one external position control signal can be supplied to different types of actuators or motors respectively, which have different actuator parameters stored for mapping the external position control signal internally to the appropriate motor control signal. 
     In an embodiment, the actuator is further configurable to operate as a stand-alone actuator, and the motor controller is further configured, for the case where the actuator is set as a stand-alone actuator, to receive on the input terminal the external position control signal, to generate based on the position control signal (and the load) the motor control signal, to control the motor by supplying the motor control signal to the motor, and to provide on the output terminal a position signal indicating a current actuator position. Thus, the same type of actuator can be used in master mode, in slave mode, or in stand-alone mode, simply by corresponding configuration, e.g. by corresponding wiring. 
     In another embodiment, the actuator further comprises a terminal box, the terminal box houses the electrical terminals of the actuator and has breakthrough areas for feeding electrical wires through the terminal box to the electrical terminals. 
     In another embodiment, the actuator further comprises manual control elements which are enclosed by the terminal box. 
     Preferably, the terminal box has a removable lid, whereby in a closed position, the removable lid is configured to protect the electrical terminals from splash liquid, and, in an open position, enabled is access to the electrical terminals and/or to the manual control elements. 
     In an embodiment, the actuator further comprises a mechanical interface with two openings on opposite sides for receiving a drive shaft. The mechanical interface has arranged at one of the openings a fastener for coupling the drive shaft to the electric motor, and one or more support rings inserted into the opposite one of the openings and configured to receive the drive shaft and to reduce lateral movement of the drive shaft with respect to a drive axis running through the two openings. 
     In yet another embodiment, the actuator further comprises an anti-rotation member arranged on a face of the actuator, and the support rings are inserted in the one of the openings that is arranged on the face of the actuator having the anti-rotation member arranged thereon. The supporting insert rings prevent or at least reduce lateral movement of the drive shaft that would otherwise result from the momentum or torque about the actuator&#39;s longitudinal axis resulting from the force of the electrical motor, particularly when the anti-rotation member and the fastener are arranged on opposite sides of the actuator. 
     In addition to an actuator, the present invention also relates to a method of operating the actuator and a computer program product comprising computer program code for controlling one or more processors of an actuator, preferably a computer program product comprising a tangible, non-transitory computer-readable medium having stored therein the computer program code. Specifically, the computer program code is configured to direct the one or more processors of the actuator to control the actuator to operate as a master or a slave to another actuator which is coupled mechanically to the actuator for driving a common load, whereby, for the case where the actuator is set as the master, the processor receives on an input terminal of the actuator an external position control signal, generates based on the position control signal (and the load) a motor control signal, e.g. a speed control signal or a torque control signal, controls a motor of the actuator by supplying the motor control signal to the motor, and controls the slave by supplying the motor control signal to an output terminal of the actuator; and whereby, for the case where the actuator is set as the slave, the processor receives on the input terminal the motor control signal supplied by the master, and controls the motor by supplying the motor control signal from the master to the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be explained in more detail, by way of example, with reference to the drawings in which: 
         FIG. 1  shows a block diagram illustrating schematically two actuators which are coupled mechanically to drive a common load and set up in a master/slave configuration. 
         FIG. 2  shows a block diagram illustrating schematically three actuators which are wired and set up in a master/slave configuration to drive a common load. 
         FIG. 3  shows different examples of piggybacking two or more actuators to drive a common mechanical load. 
         FIG. 4  shows a partial view of an actuator having a terminal box which houses the electrical terminals of the actuator and has a closed lid. 
         FIG. 5  shows the partial view of the actuator in a state where the lid of the terminal box is open. 
         FIG. 6  shows a view of the actuator with a cut-out section illustrating a mechanical interface for receiving and coupling a drive shaft to the motor of the actuator. 
         FIG. 7  shows a longitudinal cross section of the actuator illustrating the mechanical interface for receiving and coupling the drive shaft with the motor. 
         FIG. 8  shows a state diagram illustrating an exemplary sequence of transitions for detecting in an actuator that it is set up as a master. 
         FIG. 9  shows a state diagram illustrating an exemplary sequence of transitions for detecting in an actuator that it is set up as a slave. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 3, 4, 5, 6, and 7 , reference numeral  1  refers to an actuator. In  FIGS. 1 and 2 , corresponding actuators  1  are designated with reference numerals  1 M,  1 S or  1 S′, respectively, the reference numeral  1 M referring to an actuator  1  configured as a master, and reference numerals  1 S,  1 S′ referring to actuators  1  configured as slaves. As will be described later in more detail, preferably, configuration of an actuator  1  is determined dynamically and automatically; however, one skilled in the art will understand, that, alternatively, a slave or master mode can be set manually for an actuator  1 , e.g. by setting jumpers or entering a mode parameter through operating elements, etc. For example, parameterization and setting of master or slave modes, respectively, can be set via a communication interface, e.g. a communication bus of the actuators  1 ,  1 M,  1 S,  1 S′, or via an electrical terminal, e.g. output terminal U 5  which will be described later prior to the wiring of the actuators  1 ,  1 M,  1 S,  1 S′, for example. 
     As illustrated schematically in  FIG. 1 , the actuators  1 M,  1 S comprise a housing  10  and, arranged in the housing, an electric motor  12  and a motor controller  11 . For example, the electric motor  12  is a DC motor, particularly, a brushless DC (BLDC) motor. The motor controller  11  includes a control module  14 , an optional motor task module  15  and a data store  13  having stored therein one or more actuator parameters, e.g. an optional speed parameter and/or a torque parameter. The control module  14  includes a proportional-integral controller (PI controller) or another controller for generating a motor control signal sC, e.g. a speed control signal or a torque control signal (for controlling the motor current), in response to a position control signal pC received from an external control system via an electrical input terminal Y 3  and depending on the load. In an embodiment, the control module  14  or PI controller is configured to generate the motor control signal sC from the external position control signal pC and depending on the load based on the stored actuator parameters, e.g. based on the speed parameter  13  which defines for the specific actuator  1 ,  1 M,  1 S,  1 S′ or its motor  12 , respectively, a position-to-speed calculation factor, and/or based on a torque parameter which defines for the specific actuator  1 ,  1 M,  1 S,  1 S′ or its motor  12 , respectively, a position-to-torque calculation factor. In different embodiments, the motor control signal sC generated by the control module  14  or PI controller, respectively, is provided directly to the motor  12  or through the optional motor task module  15  which is implemented as a (motor) ASIC, for example, and periodically receives, e.g. every 10 ms, from the control module  14  or PI controller, respectively, the motor control signal sC. Moreover, the control module  14  includes a mode detector configured to detect whether the actuator  1 ,  1 M,  1 S,  1 S′ is arranged in a non-piggybacked setting (i.e. in conventional stand-alone mode), or whether it is set up as a master (i.e. in master mode) or a slave (i.e. in slave mode) in a piggyback configuration with one or more additional actuators  1 ,  1 M,  1 S,  1 S′, as will be explained later in more detail. 
     In an embodiment, the actuator  1 ,  1 M,  1 S,  1 S′ includes two separable units with separate housings which can be coupled electrically for exchanging control signals; one unit comprises the motor  12  and the motor task module  15 , whereas the other unit comprises the mode detector. Depending on the embodiment, the PI controller or other controller for generating the motor control signal sC and the data store  13  with the actuator parameters are implemented in the first unit, together with the motor  12 , or in the other unit, together with the mode detector. 
     The functional modules of the motor controller  11 , including the control module  14 , PI controller, mode detector and the optional motor task module  15 , are implemented as programmed software modules which direct one or more processors, as another programmed logic unit, e.g. an application-specific integrated circuit (ASIC), or fully or partly by way of discrete hardware components. 
     As illustrated in  FIGS. 6 and 7 , the actuators  1  comprise a mechanical interface  4 , with an annular opening or bore running concentrically to drive axis z through the actuator  1 , for receiving a drive shaft  3 , e.g. a cylindrical drive axle of a mechanical load L such as a valve or a damper. The mechanical interface  4  comprises mechanical fastening means  40 , i.e. a fastener such as a clamp, pin or bolt connector, for fastening and mechanically coupling the drive shaft  3  to the electrical motor  12 . Furthermore, the actuator  1  is provided with one or more tubular or ring-shaped support elements, essentially in the form of a hollow cylinder, hereafter referred to as support rings  2 ,  2 ′ for short, which are inserted into the opening of the mechanical interface  4 , opposite to the opening where the fastening means  40  are arranged. These support rings  2 ,  2 ′ fill in the gap between the drive shaft  3  and the wall of the mechanical interface  4  and reduce slackness and lateral movement of the drive shaft  3  with respect to the drive axis z. The support rings  2 ,  2 ′ are removable and come in different and/or variable diameters and thicknesses depending on the diameter of the drive shaft  3 . In an embodiment, the surface of the support rings  2 ,  2 ′ are ripped or teethed, for example. As shown in  FIGS. 6 and 7 , the actuator  1  is also provided with an anti-rotation member  5  arranged on a face  100  of the actuator  1  or its housing  10 , respectively. The anti-rotation member  5  is attached to the actuator  1  and extends beyond the width of the actuator  1 . It has one or more bores for fixing the actuator  1  to a support structure, such as a wall, a beam, a post or a pipe, for example. In installation scenarios where the anti-rotation member  5  and the fastening means  40  are arranged on opposite faces or sides of the actuator  1  or its housing  10 , respectively, the support rings  2 ,  2 ′ prevent or at least reduce lateral movement of the drive shaft  3  that would otherwise result from the momentum M or torque about the actuator&#39;s longitudinal axis resulting from the force of the electrical motor  12 . In alternative embodiments, the anti-rotation member  5  is implemented in form of one or more pins or screws, for example. 
     As illustrated in  FIGS. 4 and 5 , the actuators  1  further comprise a terminal box  6  which houses the electrical terminals  7   a ,  7   b  of the actuator  1 . The terminal box  6  has a four-sided wall that encloses the electrical terminals  7   a ,  7   b  and is either attached to the remaining housing  10  of the actuator  1  or formed as an integral part of the housing  10 . The electrical terminals  7   a  are fixed to the actuator  1  and receive the connection wires  7  directly or by way of connection terminals  7   b . Accordingly, terminals  7   a  are configured as receptacles whereas terminals  7   b  are configured as connectors which can be plugged into the receptacle. The terminal box  6  further comprises a lid  60  for opening the terminal box  6  to get access to the electrical terminals  7   a ,  7   b  and optional operating elements  8  which are also arranged in the terminal box  6 . Depending on the embodiment, for opening the terminal box  6 , the lid  60  is removed entirely from the terminal box  6  or it is rotated about an axle of a hinge by which the lid  60  is attached to the terminal box  6 . In its closed state, the lid  60  is fastened and secured to the wall of the terminal box  6  by way of screws, clamps or other fastening means. In an embodiment, a surrounding sealing ring is arranged on the lid  60  and/or on the wall of the terminal box  6  for sealing the gap between the wall of the terminal box  6  and lid  60 . The terminal box  6  further comprises a plurality of breakthrough areas  61  for feeding electrical wires  7  through the wall of the terminal box  6  for connecting the wires  7  to the electrical terminals  7   a ,  7   b . The wires  7  are run through a breakthrough  61  directly or by way of a sealing cable connector that further prevents splash water from entering the terminal box  6 . Preferably, to increase flexibility in arranging, installing and electrically wiring the actuator  1 , one or more breakthrough areas  61  are provided on all side walls of the terminal box  6  so that an opening can be broken through the wall or lid  60  of the terminal box  6  wherever it is needed or convenient in the particular set up. 
     As shown in  FIG. 2 , the electrical terminals include at least two power supply terminals V 1 , V 2 , an input terminal Y 3  for receiving control signals, and an output terminal U 5  for providing an output or a feedback signal. 
       FIG. 3  illustrates different examples of two or more actuators  1  which are arranged in a piggyback configuration for driving a common load L. Specifically, the piggybacked actuators  1  are coupled mechanically to drive the common load L cooperatively. Reference numeral PB 1  refers to a piggyback scenario where two actuators  1  are stacked on top of each other with equal orientation and coaxial alignment of their mechanical interfaces  4  such that the drive shaft  3  of the mechanical load L, here a damper, runs through the mechanical interfaces  4  of both actuators  1 . In piggyback scenario PB 2 , the two actuators  1  are arranged with a 180° opposite orientation, overlapping only with their coaxially arranged mechanical interfaces  4  such that the drive shaft  3  runs through both mechanical interfaces  4 . In piggyback scenario PB 3 , three actuators  1  are involved; two of the three actuators  1  are arranged as in scenario PB 1  and drive a first lever  81  attached to a drive shaft running through their mechanical interfaces  4 ; the third actuator  1  is arranged separate from the other two actuators and drives a second lever  82 . The three actuators  1  of piggyback scenario PB 3  are coupled mechanically in that the two levers  81 ,  82  are linked by a bar to drive the common load L. In piggyback scenario PB 4 , two actuators  1  are arranged on opposite sides of their common load L, here a damper, and have a drift shaft  3 , which is coupled to the mechanical load L, run through their mechanical interfaces  4 . One skilled in the art will understand that there are numerous other ways of mechanically coupling two or more actuators  1  for driving a common load L cooperatively, i.e. in piggyback configuration. 
       FIGS. 1 and 2  show actuators  1 M,  1 S,  1 S′ which are mechanically coupled in a piggyback scenario whereby in each case one of the actuators  1 M is set up as a master (actuator) of the other actuators  1 S,  1 S′ which are set up in each case as a slave (actuator). Specifically, the master actuator  1 M has its input terminal Y 3  connected to an external control system for receiving a position control signal pC. Furthermore, the output terminal U 5  of the master actuator  1 M is connected to the input terminal(s) Y 3  of the slave actuator(s)  1 S,  1 S′ for transferring to the slave actuators  1 S,  1 S′ a motor control signal sC. The output terminal U 5  of the slave actuators  1 S,  1 S′ are connected, for example, to the external control system for providing a position indicator (feedback) signal pN. In  FIGS. 1 and 2 , arrow F represents schematically the mechanic coupling or force feedback of the piggybacked slave actuators  1 S,  1 S′ to the master actuator  1 M. The power supply terminals V 1 , V 2  of the actuators  1 M,  1 S,  1 S′ are wired in parallel to an external power source. 
     In the following paragraphs, described with reference to  FIGS. 8 and 9  are possible sequences of steps and state transitions performed by the functional modules of the actuators  1 ,  1 M,  1 S,  1 S′ for detecting whether the actuator  1 ,  1 M,  1 S,  1 S′ is set up in stand-alone mode (no piggyback), or in a piggyback configuration in either master mode or slave mode. 
       FIG. 8  illustrates a sequence of steps and transitions T 1 , T 2 , T 3 , T 4 , T 5 , T 6 , T 7 , T 8  (T 1 -T 8 ) between different phases P 0 , P 1 , P 2 , and P 4  (P 0 -P 4 ) for detecting in an actuator  1 ,  1 M that it is configured and set up as a master. 
       FIG. 9  illustrates a sequence of steps and transitions T 1 , T 9 , T 10 , T 4 , T 11 , T 12 , T 13 , T 8  between the different phases P 0 -P 4  for detecting in an actuator  1 ,  1 S,  1 S′ that it is configured and set up as a slave. 
     In the initial start-up phase P 0 , when the actuator  1 ,  1 M,  1 S,  1 S′ is powered up, a defined initial control voltage, e.g. 9V, is provided at the output terminal U 5  of the actuator  1 ,  1 M,  1 S,  1 S′, e.g. by the motor controller  11  or control module  14 , respectively. After a defined initialization time, e.g. 200 ms, the control module  14  or mode detector, respectively, sets a phase timer to a defined duration of time for phase P 1 , e.g. 800 ms, and moves the actuator  1 ,  1 M,  1 S,  1 S′, in transition T 1 , from phase P 0  to phase P 1 . 
     In phase P 1 , the control module  14  or mode detector of the actuator  1 ,  1 M,  1 S,  1 S′, respectively, checks periodically the voltage level at its input terminal Y 3 . If the actuator  1 ,  1 S,  1 S′ is wired as a slave, the defined initial control voltage, e.g. 9V, will be measured at its input terminal Y 3 , and, as illustrated in  FIG. 9 , in transition T 9 , the control module  14  or mode detector, respectively, sets a slave indicator to true and reduces the phase timer to a reduced duration of time for phase P 1 , e.g. 400 ms. Subsequently, if the defined initial control voltage, e.g. 9V, is measured again at the input terminal Y 3  when the slave indicator is already set to true, in transition T 10 , the phase timer for the remaining duration of the time for phase P 1  is set to zero. 
     Once the defined duration of time for phase P 1  has expired, in transition T 4 , the actuator  1 ,  1 M,  1 S,  1 S′ is moved from phase P 1  to phase P 2  by its control module  14  or mode detector, respectively. 
     In phase P 2 , if the slave indicator is set to true, in transition T 11 , the control module  14  or mode detector, respectively, reduces the impedance of the actuator&#39;s input terminal Y 3  to a reduced level, e.g. from an initial 100 kΩ down to 1 kΩ. The impedance level is reduced for a brief duration of time, e.g. for 100 ms. Reducing the impedance level of the actuator&#39;s input terminal Y 3  will cause the voltage level at the output terminal U 5  of the master actuator  1 M wired to the slave actuator  1 S,  1 S′ to drop abruptly. Subsequently, e.g. after a defined duration of time, in transition T 12 , the actuator  1 ,  1 S,  1 S′ is moved to phase P 3  by its control module  14  or mode detector, respectively, and the phase timer is set to a defined duration of time for phase P 3 , e.g. 600 ms. 
     In phase P 1 , if the actuator  1 M is wired as a master, it remains in phase P 1  and provides the defined control voltage at its output terminal U 5 , as indicated in  FIG. 8  by transition T 2 , as long as there is no interrupt and the phase timer has not yet expired for phase P 1 . However, its control module  14  or mode detector will detect the abrupt drop of the voltage level at its output terminal U 5  as an interrupt signalled by one or more slave actuators  1 S,  1 S′. Consequently, as illustrated in  FIG. 8 , in transition T 3 , the control module  14  or mode detector of the actuator  1 M sets a mode indicator to “master mode” and sets the phase timer for the remaining duration of the time for phase P 1  to zero. Consequently, in transition T 4 , the master actuator  1 M is moved from phase P 1  to phase P 2  by its control module  14  or mode detector, respectively. 
     In phase P 2 , if the mode indicator is set to “master mode”, in transition T 5 , the control module  14  or mode detector of the master actuator  1 M, respectively, reduces the voltage level at its output terminal U 5  to a reduced control voltage level, e.g. 7V. Subsequently, e.g. after a defined duration of time, in transition T 6 , the actuator  1 M is moved to phase P 3  by its control module  14  or mode detector, respectively, and the phase timer is set to a defined duration of time for phase P 3 , e.g. 600 ms. While in phase P 3 , the reduced control voltage level, e.g. 7V, is maintained at the output terminal U 5  of the actuator  1 M, if its mode indicator is set to “master mode”. 
     In phase P 3 , if the slave indicator is set to true, the control module  14  or mode detector of the actuator  1 ,  1 S,  1 S′, respectively, checks periodically the voltage level at its input terminal Y 3 . If the actuator  1 ,  1 S,  1 S′ is wired as a slave, the reduced control voltage, e.g. 7V, will be measured at its input terminal Y 3 , and, as illustrated in  FIG. 9 , in transition T 13 , the control module  14  or mode detector, respectively, sets the mode indicator to “slave mode”. 
     It should be mentioned that the example presented herein describes merely the detection or indication of a slave based on a reduction of the control voltage level; however, one skilled in the art will understand that different patterns are possible which include one or more reductions and/or increases of the control voltage level. 
     Once the defined duration of time for phase P 3  has expired, in transition T 8 , the actuator  1 ,  1 M,  1 S,  1 S′ is moved from phase P 3  to phase P 4  by its control module  14  or mode detector, respectively. 
     In phase P 4 , the actuator  1 ,  1 M,  1 S,  1 S′ starts operating as a master or slave, if its mode indicator is set to “slave mode” or master mode”, respectively; otherwise, it operates as a conventional stand-alone actuator that is not configured in piggyback configuration. In an embodiment with an additional possibility for manual and/or communication-based parameterization of an actuator as master or slave, the decision about the respective mode is taken in phase P 4 , after completion of the mode detection algorithm through phases P 1 , P 2 , P 3  to P 4 . 
     In “master mode”, the control module  14  of the master actuator  1 M activates its PI controller. The PI controller receives or measures at the actuator&#39;s input terminal Y 3  the position control signal pC provided by the external control system and generates a motor control signal sC, e.g. a speed control signal or a torque control signal, based on the received position control signal pC and the load. For example, the motor control signal is generated as a pulse width modulation (PWM) signal. The control module  14  provides the generated motor control signal sC to its internal motor  12 , directly or via the motor task module  15 , and to its output terminal U 5 . 
     In “slave mode”, the control module  14  of the slave actuator  1 S,  1 S′ deactivates its PI controller. The control module  14  receives or measures at the actuator&#39;s input terminal Y 3  the motor control signal sC provided by the master actuator  1 M and provides the received motor control signal sC to its internal motor  12 , directly or via the motor task module  15 . Furthermore, in “slave mode”, the control module  14  of the slave actuator  1 S,  1 S′ provides to its output terminal U 5  a position indicator (feedback) signal pN. 
     In “stand-alone mode”, the control module  14  of the actuator  1  activates its PI controller to generate the motor control signal sC based on the position control signal pC received at its input terminal Y 3  from the external control system and depending on the load. The control module  14  provides the generated motor control signal sC to its internal motor  12 , and provides to its output terminal U 5  the position indicator (feedback) signal pN. 
     It should be noted that, in the description, the computer program code has been associated with specific functional modules and the sequence of the steps or transitions has been presented in a specific order, one skilled in the art will understand, however, that the computer program code may be structured differently and that the order of at least some of the steps or transitions could be altered, without deviating from the scope of the invention.