Abstract:
An antenna switching method of a wireless communication system capable of efficiently transmitting various signals from a plurality of transmitting antennas to a receiving unit is provided. The method includes a received signal intensity measuring step of operating an antenna switch ( 23 ) and obtaining received signal intensities of all the transmitting antennas ( 24, 25 ), a step of comparing the obtained received signal intensities of all the transmitting antennas and determining a transmitting antenna wherein the received signal intensity is the highest, a step of operating the antenna switch so that the transmitting antenna wherein the received signal intensity is the highest is connected to a transmitting circuit  22  and fixing the transmitting antenna, and a step of transmitting signals thereafter from the transmitting circuit via the fixed transmitting antenna.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an antenna switching method of a wireless communication system for selecting one antenna, excellent in a communication quality state, from a plurality of antennas and being capable of performing transmission/reception. More specifically, the invention relates to the antenna switching method of a wireless communication system for accelerating establishment of a communication state, stably transmitting/receiving a signal, and reducing battery consumption. 
     2. Description of the Related Art 
     The applicant proposes a wireless communication system that incorporates a transmitting unit in a tightening torque measuring unit attached to a rotating shaft of a tightening machine or the like and is capable of wirelessly transmitting tightening information such as a torque value and a rotating angle to a receiving unit. 
     However, the tightening torque measuring unit has one antenna on a transmitting side, and this unit rotates integrally with the rotating shaft. For this reason, when the transmitting antenna moves to a position where a quality state of the communication with a receiving unit is deteriorated due to a position where the tightening torque measuring unit stops, transmission/reception of a signal to/from the receiving unit possibly fails. 
     It is considered that a plurality of transmitting antennas is successively switched and signals are successively transmitted (for example, see Japanese Unexamined Patent Publication No. 2000-353998). In this case, however, there arises the problem that the transmitting/receiving operation in a bad communication quality state is repeated at constant intervals. 
     Therefore, a method for arranging a plurality of transmitting antennas on a tightening torque measuring unit and transmitting tightening information from the transmitting antennas all together is considered. However, since the tightening torque measuring unit rotates integrally with the rotating shaft as described above, the unit should be driven by a battery as a power source. Hence, there arises the problem that increase in power consumption causes consumption of the battery to be sped up. 
     These problems are desired to be resolved not only in the torque measuring unit but also particularly in wireless communication systems required to sequentially transmit various signals. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an antenna switching method of a wireless communication system that can transmit efficiently various signals from a plurality of transmitting antennas to a receiving unit, and particularly the antenna switching method that is suitable for a transmitting unit arranged on a member in which a plurality of transmitting antennas is rotatable and a wireless communication system using a battery-driven type transmitting unit. 
     In order to solve the above problem, the present invention provides an antenna switching method of a wireless communication system which includes: 
     a transmitting unit having a transmitting circuit for transmitting/receiving a signal, a plurality of transmitting antennas for transmitting/receiving, an antenna switch for switching any one of the plurality of the transmitting antennas to be connected to the transmitting circuit and a transmitting controller for controlling the transmitting circuit and the antenna switch, the transmitting circuit capable of transmitting a signal including a return request and transmitting/receiving another signals; and 
     a receiving unit having a receiving circuit for transmitting/receiving a signal to/from the transmitting unit, a receiving antenna connected to the receiving circuit, and a receiving controller for controlling the receiving circuit, the receiving controller transmitting a return signal from the receiving circuit when receiving the signal including the return request from the transmitting unit, 
     the antenna switching method includes: 
     a received signal intensity measuring step having a step of allowing the transmitting controller to operate the antenna switch so that any one of the transmitting antennas is connected to the transmitting circuit, transmitting the signal including the return request from the transmitting circuit via the transmitting antenna, standing by in a receiving state of the return signal, when receiving the signal including the return request, allowing the receiving controller to transmit the return signal from the receiving circuit via the receiving antenna, and allowing the transmitting controller to measure and store a received signal intensity of the return signal received by the transmitting antenna within a predetermined time, and a step of operating the antenna switch and performing the above step on all the other transmitting antennas so as to obtain received signal intensities for all the transmitting antennas; 
     a step of allowing the transmitting controller to compare the obtained received signal intensities of all the transmitting antennas and determine the transmitting antenna wherein the received signal intensity is the highest; 
     a step of allowing the transmitting controller to operate the antenna switch so that the determined transmitting antenna wherein the received signal intensity is the highest is connected to the transmitting circuit and fix the transmitting antenna; and 
     a step of allowing the transmitting controller to transmit signals thereafter from the transmitting circuit via the fixed transmitting antenna. 
     The transmitting unit operates the antenna switch so that the signals including the return request are sequentially transmitted/received from all the transmitting antennas, and measures the received signal intensities of the transmitting antennas from the receiving unit. As a result, since the transmitting antenna wherein the received signal intensity is the highest can be selected and fixed, optimization can be performed so that defective transmission/reception is reduced. 
     After the transmitting antenna is fixed, since only the fixed transmitting antenna transmits a signal, establishment of a communication state can be accelerated, and a signal can be stably transmitted/received. Further, battery consumption can be reduced, and share of a wireless frequency space can be cut down. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a wireless communication system of the present invention; 
         FIG. 2  is an explanatory diagram illustrating an embodiment in which a transmitting unit of the present invention is mounted to a tightening torque measuring unit of a tightening machine; 
         FIG. 3  is a flowchart illustrating an antenna switching method of the wireless communication system of the present invention; and 
         FIG. 4  is a sequence diagram illustrating the antenna switching method of the wireless communication system of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment in which a transmitting unit  20  of a wireless communication system  10  of the present invention is mounted to a tightening torque measuring unit  30  attachable to a rotating shaft  50  of a tightening machine is described below with reference to the drawings. 
     However, the transmitting unit  20  is not limited to application to the tightening torque measuring unit  30 , and is suitably mounted to other members, particularly, rotatable members. 
       FIG. 1  is a block diagram illustrating the wireless communication system  10  of the present invention. The wireless communication system  10  of the present invention has the transmitting unit  20  for transmitting various signals, and a receiving unit  40  for receiving signals from the transmitting unit  20 . The transmitting unit  20  can be arranged on the tightening torque measuring unit  30  as shown in  FIG. 2 . 
     &lt;Transmitting Unit  20 &gt; 
     The transmitting unit  20 , as shown in  FIG. 1 , has a transmitting circuit  22  (RF circuit) for transmitting/receiving signals, and a plurality of transmitting antennas  24 ,  25  for transmitting/receiving. An embodiment in which the two transmitting antennas (the transmitting antenna  1  ( 24 ) and the transmitting antenna  2  ( 25 )) are used is described below, but the number of the transmitting antennas may be three or more. 
     A power can be supplied to the transmitting unit  20  by a battery not shown. 
     The transmitting unit  20  can be housed in a suitable place in a tubular casing  35  of the tightening torque measuring unit  30 , described later. As shown in  FIG. 2 , it is desirable that the transmitting antenna  1  ( 24 ) and the transmitting antenna  2  ( 25 ) are arranged near an outer periphery of the casing  35  at a predetermined interval. In this embodiment, they are arranged so as to be opposed to each other via a shaft center. Further, they are arranged at opposing corners so as to be separated by ½ or more wavelength of a wireless communication frequency used by the adjacent antennas. 
     Any one of the transmitting antennas  24 ,  25  is selected so as to be electrically connected to the transmitting circuit  22  via an antenna switch  23 . 
     The transmitting circuit  22  and the antenna switch  23  are controlled by a transmitting controller  21 . 
     The transmitting controller  21  can be constituted by a CPU, a memory or the like. The transmitting controller  21  processes an output from a detection sensor  31  described later, processes various signals transmitted from the transmitting circuit  22 , measures, stores and compares received signal intensities of return signals received via the transmitting antennas  24 ,  25 . The transmitting controller  21  selects the transmitting antenna  24  or  25  and operates the antenna switch  23  so as to switch the transmitting antenna  24  or  25  that should transmit a signal. As a signal transmitted from the transmitting circuit  22 , a signal including a return request and/or tightening information detected by the detection sensor  31 , described later, can be exemplified. 
     An operation of the transmitting controller  21  is described in detail below with reference a flowchart of  FIG. 3  and a sequence diagram of  FIG. 4 . 
     &lt;Tightening Torque Measuring Unit&gt; 
     The tightening torque measuring unit  30  on which the transmitting unit  20  is arranged is, as shown in  FIG. 2 , mounted to the rotating shaft  50  of the tightening machine in a detachable or fixed manner. The tightening torque measuring unit  30  has an outer periphery surrounded by the casing  35 , and has the transmitting unit  20  arranged inside. As shown in  FIG. 1 , the tightening torque measuring unit  30  has the detection sensor  31  for electrically detecting a torque applied to the rotating shaft  50 , an amplifier  32  for amplifying the tightening information output from the detection sensor, and an A/D converter  33  for A/D-converting the amplified tightening information. The tightening information converted into a digital signal by the A/D converter  33  is transmitted to the transmitting controller  21 . 
     As the detection sensor  31  for measuring information about tightening, when a tightening torque is measured as the tightening information, a strain gauge can be exemplified. Further, when information about the rotating angle is measured as the tightening information, an encoder, a gyro sensor, a photo interrupter, or a magnetic sensor can be exemplified. When the detection sensor  31  outputs a digital signal like an encoder or a photo interrupter, the A/D converter  33  can be omitted. 
     The detection sensor  31  is not limited to the above, but various devices can be surely used. 
     In the following description, a torque is exemplified as the tightening information. 
     The tightening torque measuring unit  30  can be driven by a battery (not shown) arranged in the casing  35  as a power supply. The battery may be shared by the transmitting unit  20 . 
     A display unit  36  may be arranged on the tightening torque measuring unit  30  as shown in  FIG. 2 , so that the tightening information can be visually recognized in a direct manner. 
     &lt;Receiving Unit  40 &gt; 
     A signal transmitted from the transmitting unit  20  can be received by a receiving unit  40  shown in  FIG. 1 . 
     The receiving unit  40  has a receiving antenna  43 , a receiving circuit  42  (RF circuit) and a receiving controller  41 . A signal transmitted from the transmitting unit  20  is received by the receiving controller  41  via the receiving antenna  43  and the receiving circuit  42 . 
     Every time the receiving controller  41  receives a signal including a return request in a receiving standby state, it transmits a return signal including an RSSI value (received signal intensity value) from the receiving circuit  42  via the receiving antenna  43 . 
     When the receiving controller  41  incorporates a memory (not shown) or is connected to a display unit  45 , the received tightening information can be stored in the memory or can be suitably displayed on the display unit  45 . 
     A device identification number of the tightening torque measuring unit  30 , a time, and position information such as a tightening position are included in the signal about the tightening information transmitted from the transmitting unit  20 . This can be used for display and management of the tightening information on the receiving side. 
     The receiving unit  40  and the display unit  45  can be driven by a commercial power supply or a battery as a power supply. 
     &lt;Description of Operation&gt; 
     An operation of the antenna switch  23  of the receiving unit  40  in the wireless communication system  10  having the above constitution is described with reference to the flowchart of  FIG. 3  and the sequence diagram of  FIG. 4 . 
     A front end socket  51  of the rotating shaft  50  of the tightening machine is fitted into a bolt or a nut and started to be tightened. 
     The detection sensor  31  detects a torque applied to the rotating shaft  50 , the amplifier  32  amplifies the torque, and the A/D converter  33  A/D-converts the torque. The converted torque is transmitted to the transmitting controller  21  (step  1 ). 
     The transmitting controller  21  does not transmit a torque value from the transmitting circuit  22  until the tightening information detected by the detection sensor  31  satisfies a predetermined condition, in this embodiment, until the torque value becomes a predetermined threshold or more. (step  1 ). This is because when the torque value is the predetermined threshold or less, the rotating shaft  50  rotates, and a position of the tightening torque measuring unit  30 , namely, positions of the transmitting antennas  24 , in a rotating direction are not fixed. 
     When the tightening proceeds, the torque rises and exceeds the predetermined threshold (step  1 ), the rotating shaft  50  of the tightening machine hardly rotates, and the tightening torque measuring unit  30  attached to the rotating shaft  50  and the position in the rotating direction are approximately fixed. Therefore, the positions of the transmitting antennas  24 ,  25  are unmoving. 
     In this state, the transmitting controller  21  operates the antenna switch  23  so as to set any one of the transmitting antennas  24 ,  25  to be connected to the transmitting circuit  22  (step  2 , action  1 : for example, the transmitting antenna  1  ( 24 ) is connected to the transmitting circuit  22 ). In this state, the signal is not yet transmitted. 
     In the state that the transmitting antenna  1  ( 24 ) is connected to the transmitting circuit  22 , the transmitting controller  21  resets each RSSI integrated value to be retained to zero. A received signal intensity integrated value on the transmitting antenna  1  ( 24 ) is determined as an RSSI 1 , and a received signal intensity integrated value on the transmitting antenna  2  ( 25 ) is determined as an RSSI  2 . 
     A torque value is sequentially input into the transmitting controller  21  at every predetermined time (step  4 ). When a predetermined measured value transmitting timing comes (step  5 ) and the transmitting antennas  24 ,  25  are not fixed (steps  16  and  17 , described later) (step  6 ), the transmitting controller  21  transmits the signal including the return request and the torque value from the transmitting circuit  22  via the transmitting antenna  1  ( 24 ) (step  8 , action  2 ). As a result, measurement of RSSI of each of the transmitting antennas  24 ,  25  (a received signal intensity measuring step) is started. 
     As the measured value transmitting timing at step  5 , timing at which the torque value is input at the predetermined number of times (for example, 10 times) can be exemplified. 
     When the receiving unit  40  receives the signal including the return request (action  3 ), the receiving controller  41  returns a signal (return signal) including the received signal intensity value (RSSI) from the receiving circuit  42  via the receiving antenna  43  (action  4 ). 
     When the transmitting unit  20  receives the returns signal via the receiving antenna  24  (step  9 , action  5 ), it updates the RSSI integrated value (RSSI 1 ) of an antenna number of the transmitting antenna that transmits the signal (in this case, the transmitting antenna  1  ( 24 )) (step  11 ). The RSSI 1  is calculated by multiplying a value of original RSSI 1  (at first, zero) by the received RSSI. 
     A determination is made whether a sum of the RSSI values of the two antennas is larger than a predetermined threshold at next step  13 . As a result, a determination is made whether the transmitting antenna  24  or  25  are selected and fixed (steps  14 ,  16  and  17 ) at this step. This is described later. 
     When the return signal is received within a predetermined time and the sum of the RSSI values of both the transmitting antennas  24 ,  25  is the predetermined threshold or less (step  13 ) or when the return signal is not received (step  9 ), the transmitting controller  21  operates the antenna switch  23  so as to switch the transmitting antenna from the transmitting antenna  1  ( 24 ) to the transmitting antenna  2  ( 25 ) (step  15 , action  6 ). 
     After the antenna is switched, the tightening information is sequentially input into the transmitting controller  21  at every predetermined time similarly to the above (step  4 ), and when the predetermined measured value transmitting timing comes (step  5 ), the tightening information and the signal including the return request are transmitted from the transmitting circuit  22  via the transmitting antenna  2  ( 25 ) (step  8 , action  7 ). 
     When the receiving unit  40  receives the signal including the return request (action  8 ), the receiving controller  41  returns a signal including a received signal intensity value (RSSI) (return signal) from the receiving circuit  42  via the receiving antenna  43  (action  9 ). 
     When the transmitting unit  20  receives the return signal via the transmitting antenna  2  ( 25 ) (step  9 , action  10 , it updates the RSSI integrated value (RSSI  2 ) of the transmitting antenna  2  ( 25 ) (step  11 ). The RSSI  2  is calculated by multiplying a value of original RSSI  2  (at first, zero) by the received RSSI. 
     When the return signal is received within the predetermined time and the RSSI values of both the transmitting antennas  24 ,  25  do not satisfy the predetermined condition (step  13 ) or when the return signal is not received (step  9 ), the transmitting controller  21  operates the antenna switch  23 ) so as to again switch the transmitting antenna from the transmitting antenna  2  ( 25 ) to the transmitting antenna  1  ( 24 ) (step  15 , action  11 ). 
     At the above step, when the signal including the return request transmitted from any one of the transmitting antennas  24 ,  25  does not yet arrive at the receiving unit  40  (for example, action  13 ), the return signal is not transmitted from the receiving unit  40  (No at step  9 ). For this reason, the RSSI values are not added (action  14 ). 
     When the sum of the RSSI integrated values of both the transmitting antennas  24 ,  25  is larger than the predetermined threshold at step  13 , the transmitting controller  21  compares the RSSI values of both the transmitting antennas  24 ,  25  (step  14 , action  25 ). The transmitting controller  21  selects the transmitting antenna  24  or  25  whose RSSI value is larger and operates the antenna switch  23  so as to fix the transmitting antenna  24  or  25  (steps  16  and  17 , action  26 ). 
     For example, when the transmitting antenna  2  ( 25 ) is selected and fixed, the transmitting thereafter is performed from the transmitting antenna  2  ( 25 ) (steps  6  and  7 ). After the transmitting antenna is fixed, the signal transmitted from the transmitting unit  20  may not include the return request (actions  27  to  32 ). 
     The receiving unit  40  receives a signal including a torque value transmitted from the transmitting unit  20 , and stores it in the memory or displays it on the display unit  45 . The number of the transmitting antenna and the RSSI value may be also displayed together. 
     When the torque value does not fluctuate for predetermined time or the torque value that once rises reduces after its peak, a determination is made that one tightening operation is completed, and the transmitting of the signal including the torque value may be stopped. When new tightening is performed and the torque value becomes the predetermined threshold or more (step  1 ), the above flow is again performed. 
     In this embodiment, the step of measuring the received signal intensity is performed at step  13  under the condition that the step is repeated until the sum of the RSSI integrated values of the two antennas becomes larger than the predetermined threshold (actions  1  to  24 ). However, the step of measuring the received signal intensity can be performed once or can be performed until any one of the RSSI values becomes the predetermined threshold or more. The number of times at which the step of measuring the received signal intensity is performed is determined, and at a stage that the step is performed at that number of times, the transmitting antenna whose RSSI integrate value is the highest may be selected and fixed. 
     In the wireless communication system  10  of the present invention, the signals are sequentially transmitted/received to/from the individual transmitting antennas until the transmitting antenna wherein the received signal intensity is the highest is selected from the plurality of transmitting antennas. However, when the transmitting antenna is once selected, the signal can be transmitted from the transmitting antenna in a fixed manner. For this reason, establishment of the communication state can be accelerated, the battery consumption can be reduced, and the share of a wireless frequency space can be cut down. 
     In the above embodiment, the receiving unit  40  wirelessly communicates with one transmitting unit  20 , but a system that wirelessly communicates with the plurality of transmitting units  40  and transmits/receives signals including RSSI can be constituted. 
     A constitution may be such that a plurality of receiving antennas  23  are provided to the receiving unit  40  and a combination of the receiving antenna  23  wherein the receiving quality is the highest and the transmitting antennas  24 ,  25  is selected by the method similar to the transmitting unit  20 . 
     The above embodiment describes the case where the antenna switching method of the wireless communication system of the present invention is applied to the tightening torque measuring unit. However, the application of the present invention is not surely limited to the embodiment. 
     The present invention is useful as the antenna switching method of the wireless communication system having the plurality of transmitting antennas.