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# Tag Info

5

If you want to detect missed steps, you want an encoder. Luckily, both magnetic and optical encoders exist that easily give you 4096 steps per revolution, so even a micro-stepping stepper motor will be measured with at least one step per step. Note that some CNC mills may not necessarily detect missed steps; it's up to the operator to not program a tool ...

4

I found that the FFT of the current waveform of the stepper often shows the natural frequency harmonics of the motor+driver system AND that during a stall extra frequency harmonics appear!!! all you need is a fast, bidirectional current to voltage conversion IC and a narrow band pass filter to detect if the extra harmonics are present.

3

As a general remark, a PID controller can be designed to take into account only constraints occurring at the commanded variable - the end-effector velocity in your case - through the so-called antiwindup mechanism that is responsible for detaching the integral whenever those constraints are reached. This way, the PID is somehow informed that something "bad" ...

3

The answer is $\vec{G}$! and also any $\vec{\tau}$ torque caused by it, if the axis connecting the geometrical center of the sensor (assuming it measures torques relative to its geometrical center) to the centre of gravity of the gripper. $\vec{G} = m * \vec{g}$ where $m$ is the mass of the gripper, $g$ is the gravitational ACCELERATION, not force and G is ...

3

You need to quantify : "I measured the current through (one of the 4 wires of) my stepper motor, and it's always within a few percent of 0.5 A". A 'few percent' may be all you need to detect a little extra current during stall (if there is extra current as I would also assume but would need to prove), which can be sensed and compared to normal stepping ...

2

Unfortunately, as you've discovered, it is difficult to tell if a stepper motor is stalled because the current through the coils of a stepper motor is roughly the same if it is stalled (can't step), holding position, or stepping normally. You could definitely detect a stall with ease if you added an encoder or used a stepper motor that already had one. Why ...

2

I believe the term you're looking for is compliant control. In a compliant control system, there is a position reference and a force reference, and essentially each is allowed to actuate the joint until either achieves the reference. So, if you had a position reference of 10 and a force reference of 1, then both the force and position controllers would ...

2

If you have a simple controller (e.g. force control or position control) the factor which decides what kind of controller is it is the reference signal which has to correspond to the feedback signal. My idea was to simply tense the tendon (slowly) encompassing the object until the force sensor gives a feedback that contact has been made (+ a little grip ...

2

It sounds like you're describing a linear actuator with a pressure sensor (or strain gauge) attached to the end. To bridge that system across bluetooth, you may want to check out one of several microcontrollers -- look for bluetooth modules, a motor (or servo) controller, and analog inputs (to read the strain gauge).

2

Since you are going to have a mechanism that can draw within a square why not put a light sensor on it and use the same mechanism scan for the opponent's move? At the start of the game, scan all the squares and record the brightness value for each square. If the board is clear, all the values should be low. After your opponent is done and before each ...

1

Sensing the torque in a stepper motor is not a straightforward task. A method named Field Oriented Control is used to control the torque in a Stepper motor and several companies supply stepper motors with integrated controllers as Schneider and Nanotec. You can also look at mechaduino where they are also implementing a torque control on stepper motors, which ...

1

Microphone chips have been used as a transducer for this due to their low cost. (This being high density pressure measurements)

1

Edited: You should have put the subscript $c$ on variable $F$, because they define $F_c$ as the contact force the system is trying to maintain. Since achieving and servoing around that desired contact force is the goal, the velocity at the target state will be zero. Therefore $F_c = k_sx_r$. You’ll find the damping terms in the dynamic model - they are ...

1

This project is very nice and I was totally obvious to it thanks for spotting it ! In general the difference between FPGAs and classical ASIC integrated circuit is that FPGAs can be re-programmed by the user to emulate certain circuitry. For some task FPGAs are faster than generic processor because of their parallel nature. (1) What does processor speed ...

1

Yes you can. People built robots doing exactly that for several hundred years.

1

One option could be to use the MPU6050 IMU, or some other accelerometer. These sensors are cheap, so they will come in under your budget. With acceleration measurements, you can detect impulses caused by striking the target surface. If you are assuming light wind, then you can probably just set a threshold that on the magnitude of the impulse, classifying ...

1

In the end, end effector speed is going to be determined by joint speed + kinematics, so I would choose whichever format you want that makes life easier on you. Regarding singularities, there's no singularity caused by joint velocities, only by joint angular positions. So, if you're trying to avoid singularities but are only controlling based on velocity, ...

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