Abstract:
An exemplary system for sensing the state and position of a robot is provided. The system measures the acceleration and angular velocity of the robot and calculates a velocity, and a displacement of the robot. The state of the robot according to the acceleration and the velocity vector, of the robot, is determined. The system includes an alarm that activates according to the state of the robot. The system also compensates for any inaccuracy of the measured displacements.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a sensing system and, more particularly, to a system for sensing state and position of a robot which is traveling along a predetermined path. 
     2. Description of Related Art 
     Nowadays, robots are widely used to perform repetitious or dangerous tasks. In order to control the robot, the state and position of the robot should be known as accurately as possible at any given time. 
     Generally, the robot can calculate its present position by using an absolute or relative coordinate system. Using one or the other of the above coordinate system the robot can calculate the traveled distance and the angular displacement from a reference point. 
     As an example of the use of an absolute coordinate system, the robot uses a global positioning system (GPS) to obtain its present position and calculates the path of next movement according to the comparison between the coordinates of the present position and the coordinates of the subsequent position. However, when a robot using GPS is indoors or in areas exposed to strong electromagnetic interference, the signals from the GPS satellites may be compromised and hence the robot spatial movements may not be precise. 
     A robot using a relative coordinate system comprises a distance detection sensor for detecting a traveling distance and an angle sensor for detecting rotation angle of the robot. In general, an encoder, which can detect revolutions of a traveling wheel, is widely used as the distance detection sensor, and a gyro sensor, which can detect relative angle, is widely used as the angle sensor. However, gyros have an error rate of approximately 5˜10% (percent) of measured angle. The errors may vary depending on temperature and humidity. The errors can be accumulative such that a robot cannot follow a predetermined path. 
     What is needed, therefore, is a system which can overcome the above-mentioned problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detail of the present system, both as to its structure and operation, can best be understood by referring to the accompanying drawings, in which like reference numbers and designations refer to like elements. 
         FIG. 1  is an exemplary block diagram of the system for sensing a state and position of a robot. 
         FIG. 2  is an exemplary block diagram of a sensing part shown in  FIG. 1 . 
         FIG. 3  is an exemplary graph of velocity dispersion data of a jolted robot. 
         FIG. 4  is an exemplary graph of arrangement of a number of positioning parts shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the invention will now be described in detail below and with reference to the drawings. 
     An absolute coordinate system is established with the starting point of the robot as the origin of the Cartesian coordinates and with the x, y, and z axes as the coordinate axes. A relative coordinate system, with the center of gravity of the robot as the origin, and the x′, y′, and z′ axes as the coordinate axes is established. Before the robot moves, the relative coordinate system coincides with the absolute coordinate system. During movement of the robot, the relative coordinate system changes along with the movement of the robot. 
     Referring to  FIG. 1 , the sensing system  2  includes a sensing part  20 , a signal receiving part  22 , a data processor  24 , a state recognizing part  26 , an alarming part  28 , a compensating part  210 , and a number of positioning parts  212  which are set along the predetermined path of the robot at equal intervals. 
     The sensing part  20  includes an acceleration sensor  200  for measuring the acceleration of the robot, and a gyro sensor  202  for measuring angular velocity of the robot. 
     An exemplary block diagram of sensing part  20  is shown in  FIG. 2 . The acceleration sensor  200  includes a first acceleration sensor  2000  for measuring acceleration along the x′ axis, a second acceleration sensor  2001  for measuring acceleration along the y′ axis, and a third acceleration sensor  2002  for measuring acceleration along the z′ axis. The x′ axis, the y′ axis, and the z′ axis are orthogonal to each other. 
     The gyro sensor  202  also includes a first gyro sensor  2020  for measuring the angular velocity along the x axis, a second gyro sensor  2022  for measuring the angular velocity along the y axis, and a third gyro sensor  2023  for measuring the angular velocity along the z axis. 
     The acceleration measured by the acceleration sensor  200  and the angular velocity measured by the gyro sensor  202  are components of the relative coordinate system. 
     The signal receiving part  22  includes a first low-pass filter  220  which passes signals having frequencies at or less than 12.5 hertz (Hz), and a second low-pass filter  222  which passes signals having frequencies at or less than 50 Hz. 
     The first low-pass filter  220  is configured for filtering out high frequency distortion of the acceleration measured by the acceleration sensor  200  and transferring the filtered acceleration to the data processor  24 . 
     The second low-pass filter  222  is configured for filtering out high frequency distortion of the angular velocity measured by the gyro sensor  202  and transferring the filtered angular velocity to the data processor  24 . 
     The data processor  24  calculates the acceleration vector α of the robot and the angular velocity vector ψ of the robot according to the acceleration and angular velocity transferred from the signal receiving part  22 . The acceleration vector α of the robot and the angular velocity vector ψ of the robot are both with respect to the relative coordinate system. The acceleration vector α can be represented as an absolute acceleration value |α| and the acceleration direction with respect to the relative coordinate system. The angular velocity vector ψ can be represented as an absolute acceleration value |ψ| and the angular velocity direction with respect to the relative coordinate system. 
     In order to calculate out the acceleration vector α ∘ of the robot and the angular velocity vector ψ ∘ of the robot with respect to the absolute coordinate system, the rotation matrix C between the relative coordinate system and the absolute coordinate should be calculated by the data processor  24 . 
     The rotation matrix C can be acquired by the integral operation and matrix multiplication. It&#39;s assumed that the absolute coordinate coincides with the relative coordinate system which represents the robot at the beginning state, and after a time interval ΔT the relative coordinate system has been rotated to a new position with different coordinates relative to the absolute coordinate system. The rotational angle α of the x axis of the relative coordinate system during the time interval ΔT can be calculated by the integral operation of the rotational angular velocity along to the x axis of the relative coordinate system. Similarly, the rotational angle β of the y axis of the relative coordinate system and the rotational angle ω of the z axis of the relative coordinate system can be calculated. Therefore, the rotation matrix C between the absolute coordinate and the rotated relative coordinate system is represented by a formula: 
             C   =         [         1       0       0           0         cos   ⁢           ⁢   α             -   sin     ⁢           ⁢   α             0         sin   ⁢           ⁢   α           cos   ⁢           ⁢   α           ]     ⁡     [           cos   ⁢           ⁢   β         0         sin   ⁢           ⁢   β             0       1       0               -   sin     ⁢           ⁢   β         0         cos   ⁢           ⁢   β           ]       ⁡     [           cos   ⁢           ⁢   ω             -   sin     ⁢           ⁢   ω         0             sin   ⁢           ⁢   ω           cos   ⁢           ⁢   ω         0           0       0       1         ]             
After the time interval of nΔT, the rotation matrix C between the latest relative coordinate system and the absolute coordinate can be acquired by multiplying the preceding rotation matrix C n−1  by the latest rotation matrix C n .
 
     The data processor  24  calculates the acceleration vector α ∘ of the robot with respect to the absolute coordinate system by multiplying the acceleration vector α of the robot by the rotation matrix C between the latest relative coordinate system and the absolute coordinate system. Furthermore, a velocity vector V o  and a displacement vector S o  of the robot can be calculated, with respect to the absolute coordinate system by the integral operation of the acceleration vector α ∘ of the robot. The acceleration vector α ∘ can be represented as an absolute acceleration value |α ∘ | and the acceleration direction with respect to the absolute coordinate. The velocity vector V o  can be represented as an absolute velocity value |V ∘ | and the velocity direction with respect to the absolute coordinate. The displacement vector S o  can be represented as a displacement value |S ∘ | and the displacement direction with respect to the Cartesian coordinate. The data processor  24  transfers the velocity vector V o  of the robot with respect to the absolute coordinate system and the acceleration vector α ∘ of the robot with respect to the absolute coordinate system to the state recognizing part  26 . 
     The state recognizing part  26  is configured for recognizing the states of robot. The state of robot recognized by the state recognizing part  26  is a state of being jolted and a state of being tilted. The state recognizing part  26  recognizes whether the robot is jolted or not by use of the analysis about the dispersion data of the velocity vector V o . Referring to  FIG. 3 , an exemplary graph of velocity dispersion data of a jolted robot is shown. The dispersion data has such a character that its direction changes frequently. Therefore, the state recognizing part  26  presets a threshold time δ and a threshold frequency T. When the data representing the velocity vector with different direction has a lasting time less than the threshold time δ continuously appears, the state recognizing part  26  regards that a jolted period has occurred. For example, in  FIG. 3 , the positive data and the negative data represent opposite directions of the velocity vector V o . The lasting time δ 1  of the negative data and the lasting time δ 2  of the positive data are both less than the threshold time δ, and the positive data and the negative data continuously appear. Therefore, the state recognizing part  26  regards that a jolted period has occurred. When the frequency of the jolted period is more than the threshold frequency T, the state recognizing part  26  regards the robot as being jolted and transfers a jolted alarming instruction to the alarming part  28 . 
     The state recognizing part  26  recognizes whether the robot is tilted or not by use of the analysis about the direction angle of the acceleration vector α ∘ with respect to the absolute coordinate system. The state recognizing part  26  presets a first direction angle range (θ 1 , θ 2 ) with respect to the x axis of the absolute coordinate system, a second direction angle range (φ 1 , φ 2 ) with respect to the y axis of the absolute coordinate system, and a third direction angle range (γ 1 , γ 2 ) with respect to the z axis of the absolute coordinate system. If the direction angle of the acceleration vector α ∘ with respect to the absolute coordinate system doesn&#39;t fall into the angle range collaborative defined by the first direction angle range (θ 1 , θ 2 ), second direction angle range ( 74   1 , θ 2 ), and the third direction angle range (γ 1 , γ 2 ), the state recognizing part  26  regards the robot is tilted and transfers a tilted alarming instruction to the alarming part  28 . 
     The alarming part  28  includes an alarm  281 , which may be a device for giving an audible, visible, or other alarm. If the alarming part  28  receives a jolted alarming instruction, the alarm  281  will activate a jolted alarm. If the alarming part  28  receives a tilted alarming instruction, the alarm  281  will activate a tilted alarm. The jolted alarm and the tilted alarm can be pre-recorded in a memory, such as magnetic tape, or flash memory. The audible jolted alarm should be distinguished from the audible tilted alarm. 
     The displacement vector S o  of the robot has errors of approximately 5 to 10% (percent). The errors occur due to a constant error based on the integral calculus of the gyro sensor  202  and a change of scale factor depending on change of inner variables such as temperature and humidity. As a result, the error has to be compensated for the robot to precisely follow the predetermined path. 
     The compensating part  210  and a number of positioning parts  212  are configured for compensating the errors of the displacement vector S o . The positioning parts  212  include a main positioning part  2120  and a number of auxiliary positioning parts  2122 . Referring to  FIG. 4 , the main positioning part  2120  is set at the starting point of the robot, i.e., the original of the absolute coordinate system. The main positioning part  2120  is configured for initializing the data save in the data processor  24  when the robot is about to move. The auxiliary positioning parts  2122  are set along the predetermined path of the robot at equal intervals. Therefore, every auxiliary positioning part  2122  has determinate displacement vector S′ with respect to the main positioning part  2120 , i.e., the absolute coordinate system. Every auxiliary positioning part  2122  has a digital label  2123  for containing the information corresponding to the determinate displacement vector S′. 
     The compensating part  210  includes a reader  2100  for receiving the information contained on the digital label  2123 . When the robot passes by one of the auxiliary positioning part  2122  along the predetermined path, the reader  2100  acquires the determinate displacement vector S′ of the auxiliary positioning part  2122 . The robot has the same location with the passed auxiliary positioning part  2122 ; therefore the determinate displacement vector S′ of the auxiliary positioning part  2122  can be considered to be a correct displacement vector S′ of the robot. The compensating part  210  acquires a compensating value ΔS from the difference between the correct displacement vector S′ of the robot and the displacement vector S o  calculated by the data processor  24 . The compensating part  210  compensates the displacement vector S o  according to the compensating value ΔS before the robot meeting the subsequent auxiliary positioning part  2122 . 
     It&#39;s understood that the number of auxiliary positioning part  2122  is determined by the length of the travelling path and the accuracy of the gyro sensor  202 . For example, in the same travelling path, more accurate the gyro sensor  202  is, the less auxiliary positioning part  2122  needed. 
     As describe above, the sensing system  2  can recognize the state of a robot and compensates the displacement vector S o  of the robot due to a constant error based on integral calculus of output value of the gyro sensor  202 . Therefore, the errors of the gyro sensor  202  are not accumulated. As a result, the travelling accuracy is improved. 
     While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.