Patent Publication Number: US-6982681-B2

Title: Apparatus for detecting electromagnetic radiation, in particular for radio astronomic applications

Description:
The application is a 371 of PCT/IB03/00045 Jan. 9, 2003. 
   TECHNICAL FIELD 
   The present invention relates to an apparatus for detecting electromagnetic radiation, in particular for radio astronomic applications. 
   BACKGROUND ART 
   As is known, there are several different kinds of devices used to detect radiation from celestial objects. 
   The most common of these devices consist essentially of a parabolic surface made of materials capable of reflecting the radiation concerned (ranging in frequency from a few Ghz to several hundred Ghz), and a receiver positioned at the focus of the parabolic surface. 
   Using this structure and according to well-known physics laws, the radiation striking the inside surface of the parabolic reflector is reflected at an angle which directs it to the receiving element. 
   The latter, after detecting the incident radiation, sends corresponding signals containing information about the radiation, to a study centre where the information is analysed and processed. 
   To capture radiation from different zones in space, prior art parabolic aerials are equipped with drive means designed to vary the angle of the parabolic structure in such a way that its inside surface faces different objects in space. 
   When the angle of the aerial is varied, however, the parabolic surface is deformed on account of the weight of the aerial&#39;s load bearing structure. 
   Indeed, prior art parabolic aerials are constructed in such a way as to have a nearly perfect parabolic shape at a predetermined angle (usually 45° relative to the ground). When this angle has to be changed, the different components of the structure are subjected to varying gravitational stresses which change the position and angle of the components relative to each other and thus deform the initial parabolic arrangement. 
   It is evident that this deformation has a negative effect on the receiving performance of the aerial since the incident radiation is no longer directed at the receiving element with the same degree of precision. This means that the intensity of the signal received is greatly reduced (also bearing in mind that the signals come from very distant sources and, therefore, are in themselves very weak). 
   Moreover, the higher the reception frequency, the greater the negative effect is on the strength of the signal received. 
   To overcome this problem, prior art teaches the use of active surfaces constructed using a plurality of mobile reflecting surfaces placed side by side in such a way as to form the parabolic structure. 
   The reflecting elements are usually square or rectangular panels placed edge to edge in such a way as to form a practically uninterrupted surface. By moving the reflecting elements, as explained below, the initial shape of the surface can be maintained practically unchanged, even in the presence of varying gravitational stresses. 
   The structure is equipped with a plurality electromechanical actuators designed to vary the positions of the reflecting elements in accordance with appropriate control signals. 
   These actuators consist of an electric motor, usually a DC motor, and a piston, driven by the motor, that moves in the direction defined by the longitudinal extension of the piston itself. The upper end of each piston is connected to one or more reflecting elements whose positions are thus varied by the action of the motor. 
   The system that controls these movements through the aforementioned control signals includes a processing unit that generates the control signals by which the extent of the movement that each piston must perform (to position the reflecting elements) is communicated to each actuator in order to compensate for the deformation of the active surface due to gravitational stresses. 
   Thus, whatever the angle of the aerial, the reflecting elements can adjust their positions in such a way that the inside surface of the structure retains the ideal shape at all times, that is to say, a shape which is substantially that of a paraboloid of revolution whose curvature is appropriately adapted to improve the receiving performance of the apparatus. 
   A major disadvantage of systems such as that just described lies in the fact that all the actuators are directly connected to the processing unit and are directly addressed by the processing unit every time the reflecting elements need to be repositioned. In other words, once the processing unit has selected from its internal table the displacements required for each actuator, it sequentially selects the outputs by which it is connected to the actuators and, through these, transmits the necessary information to each actuator. 
   A solution of this kind necessarily involves the use of an inordinate quantity of cables since the direct connection of all the actuators to the processing unit requires several dozens of kilometers of cables (up to as much as around 160 km of cables for aerials 100 metres in diameter). 
   Moreover, the use of cables of considerable length to transmit signals directly to the processing unit of each single motor may contribute to the creation of significant RF interference between the control signals themselves, thus preventing not only the correct operation of the entire adjustment system but also the proper reception of weak radio astronomic signals. 
   DISCLOSURE OF THE INVENTION 
   Therefore, the aim of the present invention is to overcome the above mentioned disadvantages. 
   More specifically, the invention has for an object to provide an apparatus for detecting electromagnetic radiation, in particular for radio astronomic applications, that significantly reduces the total length of the cables used. 
   Another object of the invention is to provide an apparatus for receiving electromagnetic radiation that minimises the interference between the control signals which the processing unit addresses to the actuators. 
   The present invention also has for a secondary object to provide an apparatus for receiving electromagnetic radiation where both the actuators and the network of connections to the processing unit have a simple structure so that, in the event of a fault or malfunction, the point where maintenance is required can be located and accessed quickly and easily. 
   Another object of the invention is to improve the reception capabilities of radio astronomic aerials currently in existence so as to permit the reception of signals whose frequency is much higher than that of signals that can be received by current systems. 
   Yet another object of the invention is to provide a control system for radio astronomic receiving apparatus that can be easily applied to existing apparatus without necessitating significant and expensive modifications to the structure of the existing aerial. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other technical characteristics of the invention and its advantages will become more apparent from the detailed description, set out below, of a preferred non-restricting embodiment of the apparatus for detecting electromagnetic radiation, in particular for radio astronomic applications illustrated in the accompanying drawings, in which: 
       FIG. 1  is a block diagram of an apparatus according to the present invention; 
       FIG. 2  is a block diagram of an actuator forming part of the apparatus of  FIG. 1 ; 
       FIG. 3  is a block diagram of a component of the apparatus of  FIG. 1 ; 
       FIG. 4  illustrates the logical structure of a signal used in the apparatus of  FIG. 1 ; 
       FIG. 5  is a detailed block diagram of a part of the apparatus of  FIG. 1 ; 
       FIG. 6  is a block diagram of a component of the apparatus of  FIG. 1 ; 
       FIG. 7  is a perspective view of a part of an actuator of the apparatus of  FIG. 1 ; 
       FIG. 7   a  is a plan view of the elements illustrated in  FIG. 7 ; and 
       FIG. 8  illustrates the logical structure of a memory unit used in the apparatus of  FIG. 1 ; 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
   In the accompanying drawings, the apparatus for detecting electromagnetic radiation according to the present invention is denoted in its entirety by the numeral  1 . 
   With reference in particular to  FIG. 1 , the apparatus  1  basically comprises a receiving element  10  designed to detect electromagnetic radiation  300 , for example from celestial objects. 
   The radiation  300  normally ranges in frequency from a few Ghz to several hundred Ghz. 
   The receiving element  10  generates output signals according to the radiation  300  received and addresses these signals to a reception and processing centre where they are analysed in order to obtain desired information. 
   In order to direct the electromagnetic radiation  300  at the receiving element  10 , the apparatus  1  further comprises a surface  30 , whose shape is preferably like that of a paraboloid of revolution and whose curvature can be suitably adjusted to optimise the performance of the aerial. 
   Thanks to its reflective properties, the surface  30  directs the incident electromagnetic radiation  300  at the receiving element  10 . 
   Advantageously, the surface  30  consists of a plurality of reflecting elements  20  which are associated with each other in such a way as to form the surface  30  itself. 
   More specifically, each reflecting element  20  has a substantially plate-like structure and is positioned side by side  35  with other adjacent reflecting elements  20  in order to form the surface  30 . 
   In a preferred embodiment, the reflecting elements  20  are substantially trapezoidal in shape and are positioned edge to edge. 
   The choice of a structure of this kind makes it possible to correct the shape of the surface  30 , for example, to compensate for deformation caused by the gravitational stress to which the surface  30  is subjected when its angle is varied. 
   To perform corrections of this kind, the apparatus  1  further comprises a plurality of actuators  40 . 
   Each actuator  40  is positioned close to at least one respective reflecting element  20  and operates in such a way as to vary the latter&#39;s position. 
   In practice, each actuator  40  is connected to one or more of the reflecting elements  20  constituting the surface  30  and is designed to vary the position of the reflecting elements  20  to which it is connected in accordance with the corrections required. 
   Looking in more detail with reference to  FIG. 2 , each actuator  40  comprises a drive unit  41  and mechanical transmission means  42 . The latter are connected to the respective drive unit  41  and reflecting elements  20  and transmit to the reflecting elements  20  the motion generated by the drive unit  41 . 
   More specifically, the mechanical transmission means  42  can be moved between a plurality of working positions, each of which corresponds to at least one predetermined position of the reflecting elements  20  connected to the mechanical means  42  themselves. 
   In other words, the mechanical transmission means  42  move to different positions in accordance with the control signals received from the drive unit  41 . Consequently, the reflecting elements  20  connected to the mechanical transmission means  42  also move to different positions accordingly. 
   Still with reference to  FIG. 2 , the mechanical transmission means  42  comprise a conversion mechanism  43 , connected to the drive unit  41  and designed to convert the rotational motion generated by the drive unit  41  into the translational motion of a transmission element  44  connected to the mechanism  43 . 
   The transmission element  44  has preferably an elongated shape (see  FIG. 7 ). A first end  44   a  of the transmission element  44  is connected to the reflecting elements  20  controlled by the drive unit  41 , whilst a second end  44   b  of the transmission element  44  is connected to the conversion mechanism  43 . 
   Thanks to this structure, the rotational motion typical of an electric motor  41   a , for example, can be used to obtain a translational motion of the transmission element  44 . Thus the latter is moved substantially in a direction parallel to its longitudinal extension. These movements are used to adjust the position (and, in particular, the angle) of the reflecting elements  20  connected to the element  44 . 
   To connect the transmission element  44  to the respective reflecting elements  20 , the mechanical transmission means  42  further comprise a link plate  48 . The link plate  48  is fixed to the first end  44   a  of the transmission element  44  and connected to the respective reflecting elements  20 . 
   With reference in particular to  FIGS. 7 and 7   a , the link plate  48  presents a main through hole  49  in a substantially central position of it. 
   The elongated transmission element  44  is mounted in the main through hole  48  in such a way as to make a fixed connection with the link plate  48 . 
   The link plate  48  is in turn connected to a plurality of reflecting elements  20 . 
   In practice, the transmission element  44  consists of a rod connected at one end  44   b  to the electric motor  41   a  and, at the opposite end  44   a , to the link plate  48 . 
   The latter is preferably square in shape. A reflecting element  20  is connected to each of the four corners of the link plate  48 . 
   Thus, each reflecting element  20  is connected to four different actuators  40 , one at each of its four corners. As mentioned above, the reflecting elements  20  are preferably trapezoidal in shape. 
   In this way, a longitudinal displacement of the rods  44  can be used to obtain a variation in the position and angle of each of the reflecting elements  20 . 
   As explained in more detail below, these variations are measured and processed by an appropriate control system. 
   Thus, the apparatus  1  (see  FIG. 1 ) is equipped with a processing unit  50  connected to the actuators  40  and conveniently positioned close to the surface  30 . The processing unit  50  sends to the actuators  40  appropriate control signals  100  in order to enable the drive units  41  of the actuators  40  to move the transmission means  42  connected to them and, consequently, to drive the reflecting elements  20 . 
   Each control signal  100  incorporates, as shown schematically in  FIG. 4 , a positioning parameter  100   a  that defines an operating position of the transmission means  42  of a target actuator  40 , and, preferably, an identification code  100   b  that identifies the target actuator  40 . 
   Thus, when it becomes necessary to move one or more reflecting elements  20 , the processing unit  50  generates the control signals  100 . In order to enable the required movements to be performed, each control signal  100  (see  FIG. 4 ) contains the identification code  100   b  of the target actuator  40  to which the control signal is addressed, and a positioning parameter  100   a  defining the working position to which the transmission means  42  of the target actuator  40  must move. 
   In order to connect the processing unit  50  in a practical and functional manner to all the actuators  40 , the apparatus  1  also comprises a plurality of smart circuit blocks  60 , each of which is associated with a corresponding actuator  40 . 
   More specifically, each smart circuit block  60  is located between the processing unit  50  and the drive unit  41  of the corresponding actuator  40 . Each circuit block  60  is designed to receive as input a control signal  100  from the processing unit  50  and to output a corresponding displacement parameter  101 . 
   The latter is input to the drive unit  41  of the corresponding actuator  40  and is used to apply a movement to the reflecting elements  20  controlled by said actuator  40 . 
   Advantageously, at least one of the smart circuit blocks  60  is positioned close to the drive unit  41  of the actuator  40  associated with that circuit block  60 . More specifically, each of a predetermined number of the smart circuit blocks  60  may be positioned close to the drive unit  41  of the actuator  40  associated with that circuit block  60 . 
   In a preferred embodiment, each of the smart circuit blocks  60  is positioned close to the drive unit  41  of the actuator  40  associated with it. 
   As can be seen in  FIG. 5 , the actuators  40  are positioned according to a radial structure  70  defined by a plurality of branches  80 , each of which has one end  80   a  connected to the processing unit  50  through an interface unit  90 , described in more detail below, and which consists of a predetermined number of actuators  40  arranged in sequence. 
   In other words, to minimise the resources to be invested in cables and, at the same time, to obtain reliable and efficient connections, the actuators  40  are aligned according to a plurality of branches  80 , each of which is connected at one end  80   a , to the processing unit  50  through the interface unit  90 , as mentioned above. 
   To connect all the actuators  40  belonging to one branch  80 , the apparatus  1  comprises a plurality of transmission channels  81 , each of which is associated with a respective branch  80 . Each transmission channel  81  has an input  81   a  connected—again through the interface unit  90 —to the processing unit  50 , in order to receive from the latter the control signals  100 , and a plurality of legs  81   b  each of which connects it to the smart circuit block  60  of each of the actuators  40  belonging to the branch  80 . 
   With reference in particular to  FIG. 6 , each smart circuit block  60  comprises a main memory unit  61  designed to store the identification code “c” of the actuator  40  associated with that circuit block  60 . 
   As explained in more detail below, a component of this kind is necessary to enable each circuit block  60  to recognise the control signals  100  addressed to the actuator  40  associated with it. 
   Each circuit block  60  also includes a processing circuit  62  having a first input  62   a  connected to the main memory unit  61  and at least one second input  62   b  connected to one of the connecting legs  81   b  in order to receive the control signals  100 . 
   Thanks to the structure and connections described above, at least one of the control signals  100  is input to the processing circuit  62  which compares the identification code  100   b  contained in the control signal  100  with the identification code “c” stored in the main memory unit  61 . 
   If the two identification codes match, the processing circuit  62  outputs a displacement parameter  101  which is input to the drive unit  41  of the actuator  40 , so as to move the reflecting elements  20  associated with the actuator  40 . 
   In order to enable the control signals to reach each actuator  40 , as mentioned above, the apparatus  1  comprises an interface unit  90 , allowing communication between the processing unit  50  and the smart circuit blocks  60  of the actuators  40  and preferably positioned close to the processing unit  50 . 
   The interface unit  90  is equipped with a plurality of addressing blocks  91 , each of which is connected to the processing unit  50  and receives as input one of the control signals  100 . 
   Each addressing block  91 , advantageously consisting of a demultiplexer, is also equipped with a plurality of outputs  91   a , each of which is connected to a corresponding transmission channel  81 . 
   Thus, when a control signal  100  is input to an addressing block  91 , the latter can output it to the branch  80  to which the target actuator  40  belongs. 
   Thus, the processing unit  50  addresses the control signals  100  by first selecting the addressing block  91  to be used. The selected addressing block  91  then sends the control signal to the appropriate branch  80  through the respective transmission channel  81 . 
   Finally, the control signal  100  is received by each of the actuators  40  connected to that transmission channel  81  and each of them, through the smart circuit block  60  structure associated with it, performs the comparison operation described above so that only the drive unit  41  of the target actuator  40  actually receives the control signal and performs the required movement. 
   As mentioned above, the processing unit  50  is advantageously positioned close to the surface  30 . 
   In order to control the positioning of the reflecting elements  20  from a remote location, the apparatus  1  is equipped with an auxiliary processor  200  that may be positioned at a preset distance from the surface  30 . 
   The auxiliary processor  200  is designed to send to the processing unit  50  an auxiliary signal  110  containing at least one auxiliary parameter  110   a.    
   The purpose of the auxiliary parameter  110   a  is to identify a position of the surface  30 . In other words, the angle at which the surface  30  must be positioned is selected at the auxiliary processor  200 . 
   Then, as described below, the processing unit  50  uses this information to move the individual actuators  40 . 
   To do this, the processing unit  50 , schematically illustrated in  FIG. 3 , has an associative memory unit  51 , where all the necessary data is stored. 
   More specifically (see  FIG. 8 ), the associative memory unit  51  is designed to contain a plurality of records  400 , each of which is identified by a main parameter “p”, corresponding to a defined position of the surface  30 . 
   Each record  400  consists of a plurality of fields  410 . Each field  410  is defined by the identification code “c” of an actuator  40  and contains a positioning parameter  100   a  that identifies a position of the mechanical transmission means  42  of that actuator  40 , this position of the mechanical transmission means  42  corresponding to the above mentioned defined position of the surface  30 . 
   In practice, the associative memory unit  51  is organised like a table where each row consists of a record  400  and is identified by a main parameter “p” which associates the row with a position of the surface  30 . 
   Each row consists of a sequence of fields, each containing one positioning parameter  100   a  of the mechanical transmission means  42  for each actuator  40 . Each positioning parameter  100   a  is associated with an actuator  40  through the identification code “c” of that actuator  40 . 
   In order to correctly manage the data it receives and the programmed data in it, the processing unit  50 , further comprises a CPU  52 , connected to the associative memory unit  51  and designed to perform all the functions necessary to transmit the control signals to the actuators  40 . 
   Thus, the CPU  52 , after receiving the auxiliary signal  110 , compares the auxiliary parameter  110   a  with the main parameters “p” present in the associative memory unit  51 . If the auxiliary parameter  110   a  matches a defined main parameter “p”, the record  400  identified by the defined main parameter “p” is selected from the associative memory  51 . 
   This record  400  contains the positioning parameters  100   a  for the mechanical transmission means  42  of the actuators  40  and corresponding to the selected position of the surface  30 . 
   The CPU  52  then generates a control signal  100  corresponding to the auxiliary signal  110   a  received. 
   The control signal  100  contains the positioning parameters  100   a  present in the selected record  400 , each associated with the identification code “c” of the respective actuator  40 . 
   Thus, the control signal  100  consists of a plurality of portions, each (see  FIG. 4 ) containing a positioning parameter  100   a  and an identification code  100   b  of a target actuator  40 . 
   The control signal thus generated is sent to the appropriate addressing block  91 , so that it can be transmitted to the target actuator  40  and the respective drive unit  41  can operate accordingly. 
   At times, the step-motor  41   a , which constitutes the drive unit  41 , may not operate correctly, that is to say, the step-motor  41   a  may “break step” or “undershoot”. 
   That means that the number of steps (or revolutions) required by a control signal  100  to perform a certain movement does not exactly match the number of steps (or revolutions) actually performed by the motor in response to the control signal. 
   To avoid the possibility, however remote, of the step motor  41   a  “breaking step” (or “undershooting”), that is to say, of its failing to perform the required movement correctly, the unit  40  and the unit  60  have a built-in device designed to rapidly detect malfunctions of this type. 
   Each smart circuit block  60  (see  FIG. 6 ) is equipped with a counting register  64 , in which a defined value, representing the number of steps that the motor  41   a  must perform, is stored. 
   This defined value corresponds to the positioning parameter  100   a  contained in the main signal  100  generated by the processing unit  50 . 
   Thus, after the main signal  100  has been received, the number of steps that the motor  41   a  is supposed to perform is set in the counting register  64 . 
   To check that the step-motor  41   a  executes the command correctly, there is a cam  45  attached to a shaft of the step-motor  41   a  itself (see  FIG. 2 ). The cam  45  is coupled with a detection device  46 , preferably of optical type, located at the step-motor  41   a.    
   Each revolution of the shaft of the step-motor  41   a  corresponds to a rotation of the cam  45  through a preset number of angular positions. 
   The detection device  46 , which advantageously consists of a photocell, is designed to detect the position of the cam  45  at at least one defined angular position and to send to the smart circuit block  60  one or more corresponding electric positioning pulses  47 . 
   In practice, when movement starts, the cam  45  is located at the defined angular position, that is, facing the photocell of the device  46 . When the command received through the main signal  100  has been executed, there are two possibilities: the cam is once again at the defined angular position where it faces the photocell, or it is at a different position where it does not face the photocell. 
   If the cam  45  is located once again in the defined angular position, the detection device  46  generates the above mentioned positioning pulses  47 , preferably electrical, to communicate the information to the smart circuit block  60 . The latter, as mentioned above, is equipped with a processing circuit  62  designed to receive the pulses  47 . The processing circuit  62  also reads the counting register  64  which contains the preset value representing the number of revolutions that the step-motor  41   a  is required to perform. 
   Once the command has been executed, the processing circuit  62  compares the information received through the pulses  47  with the value in the counting register  64 . If the two values do not match, a fault signal  120  is sent to the processing unit  50 . 
   More specifically, the processing circuit  62  takes the preset value from the counting register  64  and compares it with the whole number part of it, preferably by a division operation. In this way, it determines whether the number of revolutions that the step-motor  41   a  was required to perform was a whole number or not. That is because the preset value in the counting register  64  represents the exact movement required of the drive unit  41 , including fractions of a revolution which the motor  41   a  must perform in order to position the transmission means  42  correctly. 
   The processing circuit  62  therefore compares the information in the counting register  64  (whether the number of revolutions required is a whole number or not) with the signal received from the detection device  46  (whether, after the command has been executed, the cam  45  faces the photocell or not). 
   If the pulses  47  have been received but the number of revolutions was not a whole number, or if the pulses  47  have not been received, but the number of revolutions was a whole number, the processing circuit  62  generates a fault alert signal  120  so that personnel can check the reason for the inconsistency in the processed data. 
   In a preferred embodiment, the cam  45  is made in such a way as to occupy a defined angular interval (for example, 60°). Thus, the position of the cam  45  is not detected relative to a precise angular position but relative to an angular interval corresponding to that occupied by the cam  45  itself. 
   As a further test on the operation of the apparatus  1  as a whole, the processing unit  50  periodically polls the smart circuit blocks  60  to get information about the actuators  40  connected to them. 
   In particular, with reference to  FIG. 6 , the CPU  52  of the processing unit  50  can send a first polling signal  130  to one or more of the smart circuit blocks  60  to obtain information relating to the operating state of the corresponding actuators  40 . 
   Each actuator  40  can be in one of two different conditions, namely: an operative condition, in which a movement of the transmission means  42  can be effected by the drive unit  41 ; and a non-operative condition in which the actuator  40  is disabled, that is to say, in which the corresponding transmission means  42  cannot be moved. Usually, an actuator  40  is in the non-operative condition when, for example on account of a fault or other malfunction, it cannot perform the required drive operations. 
   To store the state of each actuator  40 , each smart circuit block  60  has a status register  65  which contains a status parameter “s” representing the operating condition of the actuator  40  connected to that block  60 . In practice, the status parameter “s” consists of a bit that has the value 1 or 0 depending on the condition of the actuator  40 . 
   The first polling signal  130  generated by the CPU  52 , as mentioned above, is received by the processing unit  62  of the target smart circuit block  60 . This causes the circuit  62  to read the status register  65  and generates a first response signal  135  addressed to the processing unit  50  and containing the status parameter “s”. 
   In this way, the CPU  52  receives at defined intervals the first response signals  135  containing information relating to the operating state of the individual actuators  40 . 
   Advantageously, the processing unit  50  also includes a status memory unit  53  (see  FIG. 3 ), designed to store the data relating to the operating states of the actuators  40 . The status memory unit  53  is logically structured like a table containing a set number of defined parameters, each representing the operating state of an actuator  40 . Each time the CPU  52  receives a first response signal  135 , it compares the status parameter “s” with the parameter in the status memory unit  53  representing the state of the actuator  40  from which that first response signal  135  comes. If the two data items do not match, the CPU  52  can correct the status memory unit  53  in accordance with the new information received. 
   Another test that is performed is to ensure that the processing circuit  62  correctly reads the counting register  64 . 
   For this purpose, the CPU  52  sends to the processing circuit  62  a second polling signal  140 . On receiving the second polling signal  140 , the circuit  62  reads the defined value stored in the counting register  64  and generates as output a second response signal  145 , containing this defined value so that the processing unit  50  can receive the information. 
   Conveniently, the CPU  52  can also compare the data received through the second response signal  145  with the data stored in the associative memory unit  51 . More specifically, the CPU  52  is designed to compare the defined value received through the second response signal  145  with the corresponding parameter  100   a  contained in the associative memory unit  51 , that is, the positioning parameter  100   a  related to the actuator  40  connected to the smart circuit block  60  from which the second response signal  145  comes. 
   Alternatively or in addition to the test routines described above, the consistency between the defined value in the counting register  64  and the position of the cam  45  may also be tested periodically. 
   Thus, the CPU  52  is designed to send to one or more of the smart circuit blocks  60  a third polling signal  150 . On receiving the third polling signal  150 , the processing circuit  62  generates a corresponding third response signal  155  to communicate to the processing unit  50  information on whether or not the processing circuit  62  itself has received the pulses  47 . 
   Depending on requirements, the third response signal  155  may contain a parameter indicating whether the pulses  47  have been received or not, or a parameter representing the consistency/inconsistency between the data in the counting register  64  and the position of the cam  45 . In the former case, the CPU  52  must process and combine the information relating to the revolutions of the motor  41   a  counted and the position of the cam  45  in order to detect inconsistencies, if any. 
   In the light of the above, it is evident that the polling signals  130 ,  140  and  150  can be sent separately or at the same time, and that, consequently, the response signals  135 ,  145  and  155  may also be generated separately or at the same time. Alternatively, a single polling signal may be used, in response to which the processing circuits  62  provide all the data described above. 
   It will be understood that, if separate signals are used, the sequence of the routine may differ from that described above since the different signals may be sent and received in any order, depending on the specific characteristics of the structure used. 
   In addition, the testing signals described above may be sent and received at desired intervals, selected according to requirements. For example, the apparatus  1  may be tested practically continuously by sequentially polling all the actuators  40 , with the result that data is exchanged with each single actuator  40  every 5 seconds approximately. 
   In a preferred embodiment, the test routines are performed in response to a command from the auxiliary processor  200 , thus generating input signals addressed to the processing unit  50  to activate the tests described above. 
   To test a single actuator  40  for correct operation, should the need arise, the CPU  52  can transmit to the actuator  40  concerned a test signal  170  containing a defined displacement for the actuator  40  itself. The resulting movement actually performed can be checked either directly by an operator working close to the actuator  40 , or by the processing unit  50  for example, through one or more of the test routines described above. 
   The invention has important advantages. 
   First of all, it provides a control system for a parabolic surface whose overall wiring requirement is minimal since the motor drivers are positioned only a short distance away from the actuators and can control them directly. This also avoids the generation of interference signals. 
   Furthermore, thanks to the special type of test routines applied to each individual motor to check it for correct operation, it is possible to detect faults or malfunctions in the motors using a circuit structure that is not only very simple and economical but also compact and, hence, easy to position close to each motor. 
   Another advantage lies in the fact that the control system according to the invention as described above can easily be applied to existing aerials without necessitating substantial modifications to the structure of the apparatus to which the system is applied.