1. Field of the Invention
This invention relates to a torque sensor used for detecting the torque in a pulley-belt driving system having a belt wound on drive and driven pulleys.
2. Prior Art Statement
In the pulley-belt driving system, a belt is wound on a drive pulley driven by a motor and on a drive pulley receiving motion from the drive pulley, and the motor motion is transmitted to the driven pulley utilizing the tension in the belt. This system is used in various power transmission systems, and recently is also used for driving robot hands or fingers.
The motion of the robot hand or finger requires accurate position and power control. Therefore, for employing the pulley-belt driving system for the driving of a robot hand or finger, the torque of the system has to be controlled accurately. To achieve this end purpose, accurate measurement of torque is necessary.
FIG. 5 shows an example of the prior art torque sensor for a pulley-belt driving system.
Referring to FIG. 5, reference numeral 5 designates the pulley-belt driving system, which comprises a belt 4 fixed to a drive pulley 2 at a point and to a driven pulley 3 at a point respectively. The drive pulley 2 is driven by a motor (not shown). When the motor rotates, the pulley 2 moves to pull the belt 4 and its torque is transmitted to the driven pulley 3. A finger 6 is mounted on the driven pulley 3, and with the movement of the driven pulley 3 the finger 6 performs a job on an object 7.
The pulley-belt driving system 5 is provided with a pair of torque sensors 20. One of the torque sensors 20 provided to detect the tension of the first (upper) part 4a of the belt 4 includes a beam 23 connected to a stationary body 15 at one end, a tension pulley 21 provided on the other end of the beam 23, and a pair of strain gauges 25 provided on the opposite sides of the beam 23. The other torque sensor 20 provided to detect the tension of the second (lower) part 4b of the belt 4 includes a beam 24 connected to the stationary body 15 at one end, a tension pulley 22 provided on the other end of the beam 24 and a pair of strain gauges 26 provided on the opposite sides of the beam 24. The tension pulley 21 and 22 are urged against the respective first part 4a and second part 4b of the belt 4.
The torque M of the driven pulley 3 is calculated by the equation (1): ##EQU1## where, M: torque of the driven pulley,
R: radius of the driven pulley, PA1 .theta.: inclination angle of the belt, PA1 T.sub.1 : tension in the first part 4a of the belt, PA1 T.sub.2 : tension in the second part 4b of the belt, PA1 F.sub.1 : force applied by the tension of the first part 4a of the belt to the pulley 21, PA1 F.sub.2 : force applied by the tension of the second part 4b of the belt to the pulley 22, PA1 k: proportionality constant, PA1 V.sub.1 : output from the strain gauges 25, PA1 V.sub.2 : output from the strain gauges 26.
FIG. 6 shows another example of the prior art torque sensor. This torque sensor 30 includes a tension sensor 31 mounted on the first (upper) part 4a of a belt 4 to detect the tension T.sub.1 and a tension sensor 32 mounted on the second (lower) part 4b to detect the tension T.sub.2. Reference numeral 11 designates a tension pulley. In this case, the torque M generated at the driven pulley 3 is given as EQU M=R(T.sub.1 -T.sub.2) (2)
The above prior art torque sensors, however, have drawbacks. More specifically, the torque sensor 20 shown in FIG. 5 requires four strain gauges and two beams, so that its construction is rather complicated. In the torque sensor 30 shown in FIG. 6, the two tension sensors move together with the belt 4. Therefore, special consideration must be given to the wiring for obtaining the output signals from the tension sensors 31, 32 to avoid the damage of the wires during the motion.
Further, in the examples of FIG. 5 or 6, the tension difference (T.sub.2 -T.sub.1), or the force difference (F.sub.2 -F.sub.1) that is necessary for deriving the torque M of the driven pulley 3 is not obtained directly, but it is obtained after detecting T.sub.1, T.sub.2, F.sub.1 and F.sub.2 independently for processing detected signals. This means that additional operations are required.