Industry Robot arm

[wucc]

Dear all expert,
i am new to robotic, hope you guys can provide some comment for what i am doing.
i am proposing a robot arm for my company's operation.
the robot arm need to have 6 DOF(included gripper). just like many other toy or educational kit. but it is expected to operate 24hour a day to replace manpower.
the function is
-to grabe a small pin from location A and
-move to location B to touch a point( small forces to be applied. expected about 1kg force).
-Turn the wrist and touch the point again( small forces to be applied. expected about 1kg force).
-move to location C and drop the pin
-repeat the steps.
i need to program it on laptop and transfer program to the arm in the production, then the arm will operate itself with laptop aside.
the expected distance reach is within 40cm.
although it is for industry use, it do not need to loaded with heavy weight. the pin it should lift up is about few grams.

I am thinking of two option: one is use Servo motor another is use DC brushless motor.
If i use servo motor, i will only need 6 of servo motors like D9150S or D7150S plus the SC16A servo controller will do.?
If i use DC motor(like MO-SPG-50-180K ), i will need driver(MD10B) for each motor and motor controller(PR10A)for each motor? correct me if i am wrong cos i am really a newbie.

what other things do i need to have( except structures).

Kindly advice.

Best regards,

[aurora]

Hi there. I need more information, like:

1. size of the pin (to determined the size of the gripper)
2. production speed (to determined the required speed of the arms)
3. precision/tolerance (to determined the type of motor)
4. isn't 1 kg a bit too high?

Brush or brushless motor are not suitable for precision control, while hobbyist, RC servo motors are not meant for 24/7. I have not run any servo motors for anywhere more than 30 mins (they consume a lot of power), but typical servo motor has a life cycle of hundreds of running hours only. Metal gear servo should last longer. Stepper motor is much more durable, but they are slow and have relatively low torque (price per se).

40cm should be achievable for RC servo, preferable with lesser load. You might also want to consider a second unit, so that they can interchange regularly (30-60 mins) for the other unit to rest.

[wucc]

Hi there. I need more information, like:

1. size of the pin (to determined the size of the gripper)
2. production speed (to determined the required speed of the arms)
3. precision/tolerance (to determined the type of motor)
4. isn't 1 kg a bit too high?

Brush or brushless motor are not suitable for precision control, while hobbyist, RC servo motors are not meant for 24/7. I have not run any servo motors for anywhere more than 30 mins (they consume a lot of power), but typical servo motor has a life cycle of hundreds of running hours only. Metal gear servo should last longer. Stepper motor is much more durable, but they are slow and have relatively low torque (price per se).

40cm should be achievable for RC servo, preferable with lesser load. You might also want to consider a second unit, so that they can interchange regularly (30-60 mins) for the other unit to rest.

[wucc]

Hi Aurora,
thanks for your reply.
1: the pins size is diameter(round) from 2mm to 3mm. length is 15mm to 60mm. so the gripper need not be big. as long as it can held the pin tight.
2: the cycle is targeted to be 20second or less. it is not necessary to be 24/7. depend on the demand but must be durable.
3: the repeated position to be 0.2mm or better. is it achievable?
4: the force should less than 1kg. but i don't have a figure to show you now. the function is to move the pin to touch a spinning tool to remove the tips in both end of the pin. the tips diameter is less than 0.2mmand length is about 0.3mm or shorter. In case of force not archievable, we can program it to stay at the spinning tool longer time, so it will remove the tips also.

i need something more durable. sorry that i don't have much experience in this field. just picking up few weeks ago from RC servo and controller. but it seems not suitable for my needs now. Kindly offer some advice. thank you.

[aurora]

Hmm, I think a customize grip would be better. 0.2mm is probably too tight for this type of servo motor. And since it is for spinning tool, would that be necessary? Another concern that need to be address is the bending force on the needle, which will transfer the force back to the gripper. Hence the customize grip.

The needle length also varies, so you are likely to use some kind of feedback system, like a camera or proximity sensor.

[wucc]

Hi,
-lets open the 0.2mm tolerance to 0.5mm. will that be achievable?
-the customized gripper is needed. we will try to develop it. because we need to design a easy change gripper tip to suit different diameter pin.
- the way this arm should work is gripping the same size pins for each setup. example, we finished 10000pcs 2x30pin, then change setup to 2x50mm pin. so that we don't need the camera or sensor to detect different length.

according to your comment, step motor is more durable but slow.
if i use LINIX Stepping Motor 42BYGHD-444 Holding Torgue: 3.5Kg.cm. can it work?
do you know what is 3.5kg.cm means?
I am thinking of larget torgue for base and shoulder. and smaller torgue for elbo and wrist. strong torgue for gripper.

by using the step motor, i need to driver for each motor right? and how about the main controller? which one should i use?
thank you.

[robosang]

Woh... very long and interesting discussion.

1. RC servo is out of picture, not even those digital Servo, or Robotics servo.
2. 0.5mm accuracy at the end effector? Woh.... that is not DIY project! The more DOF you have, the higher tolerance you will need at the end effector. Since it is 6DOF, can you imagine what is the tolerance you need at each DOF to achieve 0.5mm at end effector? much less than < 0.09++ mm when you consider the arm length, stepper can achieve that we good gearing and microstepping.
3. However, stepper is a bit heavy compare with RC servo, like you said it, the arm will need to have strong shoulder and base to support the upper joint. I would suggest industrial servo that have position feedback as stepper might slip when too much of external force is applied. Again the cost is higher, much higher
4. 3.5 kg.cm means the stepper motor can pull 3.5 kg load 1 cm from the center of shaft. Imagine this, if the radius of the shaft 1cm, you can tight 3.5 kg of load and the stepper motor can rotate. That's is theoretically, most will not achieve what is written in spec . So when the length of the mechanism or arm increase, the torque decreased.
5. Another concern is the weight of the item (needle) you want to carry or pick.... 1 kg is very heavy for a small robotic arm......
6. Durable.... again all those hobbyist stuff is out of the way!
7. Using RC servo that have 19 kg.cm cannot carry 1 kg load for 5 DOF or less, do you think a stepper with 3.5kg.cm can do the work?

[aurora]

If I get it right, the 0.2mm and 0.5mm tolerance is actually for the insertion tolerance of the needle to the spinning tool. The tolerance for for the x-y plane on the disk is not a concern right?

If you want to achieve better accuracy, you may need to reduce the DOF, and design something that specifically suit the purpose. Robosang has a point there, 0.5mm is very ambition for RC servo.

Anyway, if you have the budget to try, well, you can always try! (Well, I like to know also how well/accurate RC servo can be)

[aurora]

If the tolerance is limited only to single axis, you can try installing a mechanical limit that prevent the gripper from pushing too far. For that to work, your gripper nedd to hold the needle at very precise location too.

[wucc]

you are right the 0.2-0.5mm tolerance is for insertion. the pins need to carry is only few gram( less than 5 gram mostly).
Is there possible to use RC servo and step motor together in a robotic arm?
if the Base servo have the torgue 19kg.cm, how much weight should i control the rest of the arm to be operate efficiently?
i know robotic parts are costy, so i try to build something that have more value instead of pure hobby. otherwise not many people can afford this hobby.

If I get it right, the 0.2mm and 0.5mm tolerance is actually for the insertion tolerance of the needle to the spinning tool. The tolerance for for the x-y plane on the disk is not a concern right?

If you want to achieve better accuracy, you may need to reduce the DOF, and design something that specifically suit the purpose. Robosang has a point there, 0.5mm is very ambition for RC servo.

Anyway, if you have the budget to try, well, you can always try! (Well, I like to know also how well/accurate RC servo can be)