Then we start to calculate the torque at each motor like picture 3 and the equations of this picture is: The robot arm must be in this case when calculating the torque of motors as shown in picture 2 The critical case is in horizontal position that gives the biggest perpendicular distance as shown in picture 1 and it's obvious that 元 is the biggest distance in horizontal position. To determine the required torque we choose the critical case which the weight of the body causes the biggest torque and choose motor equal to this torque, and it's preferred to give safety factor equal to 1.5 for smooth motion without vibrations. The torque law is T=F.L and the affecting force on the robotic arm is its weight W=m.gīut when buying the motors you will find the torque unit in (kg.cm) so the law used in calculate the torque is T=m.L ,where m is the mass the part and L is the perpendicular distance from rotation axis of motor to center of gravity of the body. So it's better to use servo motors in this application. When using stepper motors, the theory of its motion is to move step by step through poles, but it's not having a feedback system so if there is a lag because of inertia it won't go back to its right position. When using standard DC motor, you will face two problems, (angle controlling - speed controlling), if you give the motor maximum voltage it will be very fast but unable to control the angle of rotation, and if you give small voltage to decrease the speed to overcome angle control problem the torque will be small and unable to move the required load. There are three types of direct current motors can be used (standard DC motor - Stepper motor - Servo motor), but the best of them in this application is Servo motor because it gives a great accurate angle of rotation due to the encoder in servo that measures the difference between reference and required angle and go to the position with great accuracy, and if there is an Inertia during motion it returns to the required angle so it's a closed loop with a feedback system, in addition to its suitable price according to its torque.
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