Brandle Dxc

8/18/2019 Brandle Dxc

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Semester Project

1st November 2011

Double Pendulum Robotic Arm with

Toothed Clutches

Christoph I. Brändle

Supervisors: N. Maheshwari

Prof. Dr. F. Iida November 2011


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Acknowledgements

I want to thank all the people, who helped me working through this

semester thesis:

• Prof. Dr. Fumiya for offering the opportunity to work on a interesting

and pleasant thesis and for supervising

• Nandan Maheshwari for supervising in a very friendly manner

• The ASL workshop team and especially Pascal Wespe for technical ad-

vices

• Keith Gunura and Derek Leach for helping out with details in the lab

• Fabian Guenther for constructional advices

• Other people, who don’t want to be mentioned, but helped me working


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Contents

1 Introduction 5

2 Concept 72.1 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Static Calculation . . . . . . . . . . . . . . . . . . . . . . . . . 82.3 Dynamic Calculation . . . . . . . . . . . . . . . . . . . . . . . 9

2.3.1 Motor Choice . . . . . . . . . . . . . . . . . . . . . . . 92.3.2 Drive Simulation . . . . . . . . . . . . . . . . . . . . . 102.3.3 Clutch Choice . . . . . . . . . . . . . . . . . . . . . . . 13

2.4 Mechanical Concept . . . . . . . . . . . . . . . . . . . . . . . 13

3 Mechanical Design 173.1 Table-Mount Drive . . . . . . . . . . . . . . . . . . . . . . . . 19

3.1.1 Mounting the Table-Mount Drive . . . . . . . . . . . . 193.1.2 Dimensioning of the Main Shaft . . . . . . . . . . . . . 21

3.2 Arm Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.1 Mounting the Arm Drive . . . . . . . . . . . . . . . . . 243.2.2 Dimensioning the Belt Drive Shaft . . . . . . . . . . . 253.2.3 Elbow Joint . . . . . . . . . . . . . . . . . . . . . . . . 263.2.4 Variability . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4 Electronics Design 31

4.1 Motor controller . . . . . . . . . . . . . . . . . . . . . . . . . . 314.2 Encoders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334.3 Clutch Control . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5 Conclusion 375.1 Test driving and Discussion . . . . . . . . . . . . . . . . . . . 375.2 Future Topics . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

A Appendix 41A.1 Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

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CONTENTS

A.2 Pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46A.3 Data CD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

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1. Introduction

This report describes how a robotic arm with two joints and two links withclutches to each of the drives is developed at the Bio-Inspired Robotics Lab(BIRL), ETH Zurich.

The objective of this semester project is to evaluate the usefulness of rotationaltoothed clutches for multimodal actuation, e.g. in active and passive mode.The designed arm should serve as a platform to do research on merits anddemerits of multimodal drives. Also, the clutche’s practicbility for a long termproject of the BIRL is proved, i.e. a four legged leopard-like robot. It isconsidered, whether the construction principle of this arm is able to locomotesuch a robot.

To evaluate the performance of the arm, the goal is set to the following. Thearm is able to throw small objects at decent speeds and in a ”bio-inspired”manner. In order to simulate natural movements, like those of a human,clutches are added to the drives. This way the arm can be driven in variousmodes, fully active and always connected to the motor shaft, completely pas-sive or in a combined way of both. This doesn’t lead directly to the evaluationof the performance as a leg, but offers space for other studies.

The path of the development leads through conception, preliminary calcula-tions, searching for suitable components, mechanical design, manufacturing,assembly, installing and configuring the electronics and test driving.

This document is rather understood as manual and guideline for handling andoperating the resulting product to facilitate further developments on it’s base.

For the mechanical guideline refer to chapter 3.

For the electronic guideline refer to chapter 4

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2. Concept

The basic idea for the arm is quite simple. It consists of a double pendulum,that has two actuated joints, that can be operated independently in active orpassive mode. In the active mode the joint is coupled with the driving motorand fully actuated. In the passive mode the joint is free and experiences onlyforce from the friction in the bearings and drag. The idea is easily visualizedin picture 2.1.

Figure 2.1: Basic idea of a double pendulum actuated arm

2.1 Specifications

In order to estimate the dimensions of the whole arm and the drives, somespecifications have to be set. The specifications for the first attempt are:

• lift weight with outstretched arm (up to 1 kg)

• throw an object not too slowly (0.5 kg at 40km/h, object flies 12m at41◦ launch)

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2.2. Static Calculation

• throw in upper position (like a baseball player, see pic. 2.2)

•

dimensions resemble human arm (link length approx. 0.3m)• one full revolution with each link possible

Figure 2.2: A baseball player throwing a ball

2.2 Static Calculation

To fulfil said specifications some simple calculations are made to evaluate therequired torque. Which again sets the type of the motor and the clutch thatis required.

The static load is set to the following:

•

link 1 - 0.35m, 0.5kg• link 2 - 0.3m, 0.5kg

• gripper with payload - 1kg

• drive on ”elbow” joint - 2kg

Above configuration leads to a torque load of 16.75Nm in the ”shoulder” joint.This is the case, if the arm is outstretched and standing still. So the clutchand the motor have to be able to handle a torque of at least 17Nm.

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2.3. Dynamic Calculation

link1 link2drive

gripper + payload

0.5kg2kg

0.5kg1kg

Figure 2.3: Load on outstretched arm

2.3 Dynamic Calculation

The specification, that the arm should be propelled results also in a torquerequirement. The goal is to be able to throw the payload at 40km/h withthe second link only. This is a conservative approach to achieve the primarygoal of 40km/h with the whole arm. The first link is assumed to be rigid andstanding still.

The starting point of the calculation is the following:

• speed of payload at goal is 40km/h

• start from bottom position (0◦)

• goal at top position (180◦)

The whole calculation involves the dynamics of a single pendulum, which issimple (but nonlinear), and the dynamics of the used motor. In consequence,this calculation is recursive and a suiting motor has to be chosen accordingly.

2.3.1 Motor Choice

The drive for the arm should be lightweight and powerful, so the first thought isto make use of a model plane motor. This path, though, had to be abandoned,because such motors are designed to be operated at much higher speeds (>400rpm) and are commuted electronically. Followingly there are no suitablecontrollers for the operation range for a handling arm. This limits the choiceto DC motors, which are heavy, but easy to control.

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As the lab has made good experiences with maxon motors, Maxon RE 40, 48Vis chosen.

The important motor data:

• nominal speed 7000rpm

• stall torque 2.5Nm (1.5Nm at 25 A)

• motor 0.48kg, gear head 0.62kg

• speed / torque gradient 3.04 rpmmNm

For more data, refer to the motor data sheet in the data CD

The next task is to set the gear ratio of the gear head suitingly. So therotational speed of the second link is needed.

Turning speed of second link:

ω =

v

r =

12m/s

0.3m = 40rad/s = 382rpmGear Ratio:

b = 382rpm

7000rpm =

1

18.3

In this range gear ratios of 1:15 and 1:19 are available. For enough torque athigher speeds and high maximum speed 1:15 is chosen.

By combining RE 40 with a planetary gear head with a ratio of 1:15 , amomentary torque of up to 22.5Nm can be realized for about 1 second. One

second might seem short, but the following simulation shows, that the armexecutes a swing from 0◦ to 180◦ in 0.12 second. So even though the systemwas simplified for the simulation, there is enough margin.

2.3.2 Drive Simulation

The dynamics of the single pendulum and the motor is simplified and modelledin MATLABR as follows:

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Pendulum:

φ̈(t) = −gl sin(φ(t)) − cf φ̇(t) + 1

ml2M (t)

g grav. constant, 9.81l link length, 0,3mm point mass on end of link, 0.5kgcf combined friction factor, estimated to 0.9M (t) motor torque

Motor:

M (t) = b(n0 − n(t))∆M

∆n

n(t) = b φ̇(t)60

2π

n0 no load speed, 7580rpm

n(t) speed in rpm∆n∆M

gradient of speed / torque line, 3040rpmNm

b gear ratio, 15

The maximum torque is limited to 17.5Nm due to subsequent limitations bythe clutch.

The result can be seen in figure 2.4. Although there is a decrease in torque dueto high rotational speed of the motor, the target speed of 40km/h is reachedby the second link in 0.12 seconds at a position of about 150◦. So there is stillplayroom regarding speed of the first link.

The speed of the first link isn’t simulated, because it’s weight is, in contraryto the first link, very dependent on the mechanical design of the whole arm.However since 40km/h is achieved by the second link only, the speed of thefirst link can be regarded as additional bonus boost.

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T o r q u e [ N m ]

Time

V e l o c i t y [ k m / h ]

Time

P o s i t i o n [ ◦ ]

Time

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

0 0.

02 0.

04 0.

06 0.

08 0.

1 0.

12 0.

14

0

5

10

15

20

0

10

20

30

40

50

0

50

100

150

200

Figure 2.4: Simulation of the drive dynamics

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2.4. Mechanical Concept

2.3.3 Clutch Choice

For use in an robotic arm, also a clutch should be compact, lightweight and asstrong as possible. Further the clutches should be controlled to switch frompassive to active mode and back. This leads to clutches which are magneticallyactuated. There are two types of such clutches, friction and toothed clutches.

Friction clutches use braking surfaces, which are pressed together when en-gaged. They can be switched on anytime and at almost any speeds. At aweight of 0.5kg they can produce about 5Nm of holding torque, which is notsufficient in this particular application, where we need at least 17Nm.

Toothed clutches have the drawback, that they can only be engaged at acertain relative speed1 of the two shafts. In contrast they can handle a threetimes larger holding torque at similar weights.

So the final choice is the model 546-12-34NF form Miki Pulley. It is a toothedclutch, that can be operated in both turning directions and can be engaged atany rotational position. It can transmit up to 17.5Nm of torque and weightsabout 0.5kg, which is still quite heavy.

2.4 Mechanical Concept

The main task in designing the double pendulum arm is, how and where tomount the two drives and more important the clutches. They are bulky, heavyand have to be mounted specially. After thorough consideration, the set upseen in picture 2.5 is chosen.

The drive and the clutches for the shoulder joint are mounted linearly on abase, that is mounted on a supporting surface e.g. a table. In this construction,the arm is only supported on one side of the load, which leads to an enormousmain shaft with 20mm diameter to resist the bending moment.

The drive for the ”elbow” joint is mounted rather complicatedly. Because thewhole drive consisting of motor, clutch, magnetic clutch and casing weightsabout 2kg, it is not very sensible to mount it in the joint. It would decreasethe arm’s lifting performance about 6.5Nm. So it is decided to be mountedlevel with the first drive. Though due to collision it can’t be mounted on thesame side. The transmission to the joint occurs via belt drive.

For modularity, the first link is manufactured out of an Item profile. This

1In this case 50rpm of relative speed

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Figure 2.5: Mechanical layout, black: motor with gear head, orange: clutches, blue:belt drive wheels, red: various bearings

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way, the whole arm gets variable. The moment of inertia can almost freelybe modified by shifting the center of mass and the length of the arm can be

modified, too.

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3. Mechanical Design

Here, the most important components are described in detail. Purpose, safeoperation, mounting / dismounting and variability are explained.

The most important operation limitations:

• Always, at any time, stay clear of the arm and the plain of it’srotation! You will be hurt seriously in case of a collision.

• Do not engage the clutches when not moving. It can happen, that theteeth don’t interlock straightaway. This can harm the teeth.

• Do not execute more than 3 full rotations with the first link. The cablescan be pulled out.

clutch engagement (max. relative speed) 50rpm (general) / 100rpm (2nd link, no load)

max. rot. speed of maxon drive 450rpm

max. rot. speed of 1st link 200rpm

max. rot. speed of 2nd link 450rpm

max. load to launch at 40km/h 0.5kg

max. load to lift w. outstretched arm 1.5kg

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Figure 3.1: Table-mount drive, from left to right: (1) maxon drive with encoder, (2)holding plate for drive, (3) coupling, (4) block with bearings for clutch shaft, (5) clutchwith clutch shaft, (6) main shaft, (7) fixed bearing (with locking nut, spacer, cap andclamping collar), (8) block with bearing for main shaft, (9) additional encoder (on top of block), (10) fixture to the first link, (11) base plate

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3.1. Table-Mount Drive

3.1 Table-Mount Drive

The table-mount drive is designed as visible in picture 3.1. All is fixed on thebase plate (1) that in turn can be bolted down to a table. The blocks (2), (4)and (8) are pinned for precise alignment and are bolted to the base plate. Thebearing blocks (4) and (8) are constructed according to the fixed / floatingbearing concept. Where the fixed bearing (7) is a complex construction dueto accessibility.

3.1.1 Mounting the Table-Mount Drive

The most difficult parts to be assembled in this group are the clutch and thefixed bearing.

Clutch

The toothed clutch (5) has to be mount in a not very intuitive way. For furtherinformation refer to the catalog page 138 of miki pulley. The actual mountingis according to the picture 3.2

Figure 3.2: Drawing of clutch and fixed bearing assembly

It is a two shaft design. The precise positioning and alignment of the clutchbody and the clutch disk is crucial for proper functioning. The air gap between

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disk and body has to be kept at 0.15∼0.3mm and the parallel alignment of thetwo parts has to be below 0.04mm. The parallel alignment is actually quite

tough to realize in this design and has to be worked out manually by mountingand dismounting until the value fits, preferably checking with a dial gauge.

Fixed Bearing

Picture 3.2 illustrates the assembly of the fixed bearing. First of all, lockingnut, spacer, cap, bearing and the clamping collar have to be put in this order onto the shaft. The clamping collar is to be set on the right place and tightened.It represents a stop for the bearing. Due to installability, a shoulder can’t be

machined here. Then the bearing is locked on the shaft with help of the spacerand the locking nut. The now mounted shaft can be inserted into the blockand fixed with the cap.

A note for dismounting: The small drive wheel for the encoder on the 20mmmain shaft is glued. So if the main shaft has to be disassembled, the glue hasto be made hot with a heat gun. For remounting glue again, of course.

Base Plate

There is only one way to put together all the parts. The base plate has to beput in place as the last part. Drive, coupling, bearing blocks, clutch have tobe aligned on a table. Then the pins have to be placed and finally the baseplate is carefully mount to all the blocks (2,4,8) at the same time.

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Figure 3.3: Explosion: table-mount drive

Fixture to First Link

The arm is fixed to the table-mount drive by a clamping set and a housing,that has anti-rotation rails ((10) on picture 3.1, rightmost part on picture 3.3).The link can be fixed at any position on the Item profile without any drawbackto the construction. The dynamics change of course massively. The link canalso be positioned such, that the arm is in balance and does not have to liftit’s weight. This way the drive on link 1 can be used as counterweight.

3.1.2 Dimensioning of the Main Shaft

The main shaft is designed as a cantilever and has to withstand the momentresulting from the throwing motion and the static moment. It is assumed, thatthe worst case happens, when the arm executes a swing at full speed (200rpmfirst link, 450rpm second link) in the lower position (0◦) with a load of 0.5kg.

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Figure 3.4: Lengths for the calculation of the moments

The arm and arm drive induce a static moment M stat on the main shaft, thatis not negligible:

M stat =

i(migli) = 11.1Nm

marm 2.25kglarm 0.086mmdrivewheel 0.5kgldrivewheel 0.15mmhousing 1.7kglhousing 0.18mm

clutch 0.5kg

lclutch 0.19mmcoupling 0.3kglcoupling 0.26mmdrive 1.1kgldrive 0.35m

The movement causes the much bigger moment M rot:

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3.2. Arm Drive

M rot = larm(m pr pω21 + 2m jr pω

21 + mua(2r pω

21 + ruaω

22

) + ml(2r pω21 + 2ruaω

22

)) =96.1Nm

m p mass Item profile 0.65kgr p half length profile 0.17mm j mass joint parts 0.8kgmua mass underarm 0.5kgrua half length underarm 0.15mml mass load (with future gripper) 0.5kgω1 rot. speed 1

st link 0.5kgω2 rot. speed 2

nd link 0.19m

So in total the moment is

M tot = M rot + M stat = 107.2Nm

The maximum stress in the profile is

σb = M tot

W y=

32M totπd3

= 136.5 N mm2

Assuming the steel to have an elastic limit of at least 200 N mm2

we have a safety

factor of at least 1.5. Of course the operation of the arm is not smooth and caneven be described as jerky, however the steel is of good quality (probably inthe range of 300 N

mm2) and the load doesn’t happen always. Even if something

not considered happens, the ultimate tensile strength is at 700 N mm2

more thanenough to avoid breaking and flying apart.

The arm is not designed according to endurance strength, because it isn’tassumed to be operated for more than 1000 throwing cycles. So: Do notoperate permanently!

3.2 Arm Drive

The drive for the second link is positioned on the first link and transmits it’storque via belt drive to the second link. This design results from the attempt toreduce inertia of the first link. This way, the inertia of the first link is reducedmore than 30% and more torque can be employed on payload handling.

As visible on picture 3.5 the drive consists of belt drive wheel, clutch, coupling

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3.2. Arm Drive

and the maxon drive. All the parts are mount on a solid built frame, that ispinned and bolted together to transmit the torque.

Figure 3.5: Arm drive: (1) belt drive wheel, (2) clutch, (3) coupling, (4) maxon drive, (5)bottom plate, (6) belt tensioning plate

3.2.1 Mounting the Arm Drive

The main part of mounting the arm drive is to assemble the clutch and thedrive wheel on it’s shaft and finally tensioning the drive belt.

The clutch and the drive wheel are again mount not very intuitionally. Referonce more to the catalog page 138 of miki pulley. This time the design isa through shaft version. The drive wheel is mount on bearings and doesn’t

transmit any torque except if the clutch is engaged, see drawing 3.7. The twoparts, drive wheel and clutch, are held in place solely by a clamping collar,next to the drive wheel on the drawing.

To assemble the drive, the order on the explosion picture 3.6 has to be followed.The spacers are not to be forgotten, since they are the key to positioning thecomponents.

After the Frame including the bottom plate ((5) in pic. 3.5) is mount, it isinserted to the Item profile and fixed loosely with T-slot nuts. The tensioningplate (6) is attached and it’s middle bolt driven into the bottom plate. By

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3.2. Arm Drive

tightening it, the belt gets it’s tension required for proper function. The beltshould be, according to the catalog information, tensioned up to 700N, but

here it is tensioned by touch, since there is no tool available to measure.

Figure 3.6: Explosion: arm drive

Figure 3.7: Section: arm drive

3.2.2 Dimensioning the Belt Drive Shaft

The belt drive shaft is the most risky part in the design. It is underdimensionedquite a lot. The problem here is, that the clutch has only a passage of 10mm.

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3.2. Arm Drive

The shaft going through the clutch should only transmit torque and shouldnot be exposed to any bending stress. But in this case there is a bending load

due to tensioning of the belt drive.

Transmitting 17.5Nm causes a maximum stress on the surface (d = 10mm) of:

σT = M T W p

= 16M T

πd3 = 89.1 N

mm2

Additionally there is a maximum bending moment between the bearings of the drive wheel1. Assuming the support permits small rotation around itself,the resulting bending stress is

σB =

M b,max

W y =

32Qlalb

πd3(la + lb) = 311 N

mm2

Q load from drive belt 2F belt = 1300N la distance load to left support 79mmlb distance load to right support 33mmd diameter shaft 10mm

In the worst case we get a combination of bending and torsional stress (tobe calculated according to maximum shear theory). For dimensioning σB of 311 N

mm2 is already enough to say, that the limit of 200 N

mm2 is exceeded. There

is even a keyway in the shaft, that reduces the diameter and deteriorates thestress situation even more. So the belt tension should be kept at a reasonablelevel.

If the shaft should break, quite likely to happen some time, the shaft has to bemanufactured out of a stronger material than stainless steel. An elastic limitof 200 N

mm2is very moderate and is outperformed by any tempering steel (up to

∼ 1500 N mm2

).

3.2.3 Elbow Joint

The elbow joint is kept simple, see pictures 3.8 and 3.9. There are two clampingsets in the drive wheel and in the second link, that join the three parts firmly.The second link is to be extended by a gripper.

It has also to be said, that the friction in the elbow joint is quite high dueto the rubber drive belt and the bending moment caused by the belt tension.To reduce friction, the belt tension can be reduced, the elbow joint can be

1where the belt is pulling

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3.2. Arm Drive

redesigned such that the drive wheel gets closer to the bearing, or the bearingscan be replaced with larger ones.

Figure 3.8: Elbow joint

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3.2. Arm Drive

Figure 3.9: Explosion: elbow joint and second link

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3.3. Manufacturing

3.2.4 Variability

Some mechanical parameters of the arm can be changed easily. So in case of a system identification, caution is required, not to change them accidentally.The variable parameters are:

• The position, where the first link is attached to the shoulder joint -The arm drive can be used as counterweight to increase the dynamicperformance of the arm, although that reduces the similarity of the wholedesign to the human arm.

• Both link lengths - By installing longer links the arm can be extended.

This however involves also installing a longer drive belt. The second linkcan’t be longer than the first due to clearance.

3.3 Manufacturing

All the home-made parts are manufactured in the ASL workshop, togetherwith Pascal Wespe, the technician and mechanical advisor of BIRL. The man-ufacturing is done in close collaboration with him. Almost all the parts are

machined directly out of the 3D model, leaving out the blueprint-step.

Some pictures can be viewed in the appandix.

All the NX7.5 3D models are contained in the data CD.

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3.3. Manufacturing

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4. Electronics Design

In order to control the drives, read the sensors and to operate the clutches,there is need for an electronic controller. The whole structure has to be de-signed and wired accordingly. For simple test driving and demonstrations, thestructure is operated with MATLAB R. Although it is said, that MATLAB R

doesn’t handle real time operations very well without thorough layout, it issufficient for testing. The whole structure is shown on figure 4.1

4.1 Motor controller

The motor controller is chosen from the catalog of Maxon Motor, suiting theRE40 motor. Since the motor needs the maximum possible current of 25A1,there are only two models, EPOS2 70V/10A and 4-Q-EC DES 70V/10A. TheEPOS2 70V/10V is chosen, because of the price and the versatility. It can beapplied for velocity, torque and even position control.

Two EPOS2 are needed for two motors. They are connected to each other viaCAN-bus2. Nr.1 EPOS2 is connected to the computer with MATLAB R.

They are fed by a powerful power supply, that can deliver up to 25A at 48V

DC.Additionally, the clutches and all the encoders are connected, too. The EPOS2has additional digital in-/outputs and analog inputs, which come in very handyfor controlling the whole structure at once.

The configuring of the controllers and the motors is done with the programEPOS Studio, delivered by Maxon Motor.

1for 1 second2with CAN wire from J8 (EPOS2 nr.1) to J7 (EPOS2 nr.2)

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4.1. Motor controller

0

0

2

2

10

2

&

1 0

2

2

2 0/10.1

2 0/10

.2

2

10Ω

10Ω

10Ω

10Ω

.

Figure 4.1: Overview of the electronic design of the arm, svg-file on data CD for more detail

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4.2. Encoders

4.2 Encoders

There are two different types of encoders for measuring the angular positionsof the joints and the motors. The maxon motors come with optional encoders3

directly mount on the motor. They work very well with EPOS2 and are easyto use. However, since they are mount on the back side of the motor, they cannot measure what is happening after the clutch, which of course disengagesfrom the motor shaft sometimes. To measure the positions in the passive,disengaged mode, there is need for additional encoders directly mount on theshaft in the joints. Contactless hall sensor made by Novotechnik4 are used.

The encoders of Maxon Motor are plugged to the according socket5 on the

EPOS2 and are fine. The hall sensors of Novotechnik are read via the signalconnector J5A, pic.4.2. Pin 5 and 6 are used. They are analog input 1, 5is the negative and 6 the positive signal. The hall sensor generates a signal,that reaches from 0.1V to 10V, but the analog input on EPOS2 can only readsignals up to 5V. So a simple voltage divider is connected, visible in pic. 4.3.The sensors are fed with 24V DC.

Figure 4.2: Signal connector J5A, numbering

3Encoder MR, Type L, 256-1024 CPT, 3 channels, with line driver4RFC 4801-636-111-2015J4

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4.2. Encoders

0

&

1

/1

.1

1Ω

1Ω

Figure 4.3: Detail of sensor and clutch connection

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4.3. Clutch Control

4.3 Clutch Control

The clutches are controlled via the digital output 4 of the signal connectorJ5 pic. 4.4, that is a high current output6. For this the digital output of theEPOS2 needs to be fed with 5V DC to the pin 9, +V Opto IN. The groundis connected to pin 14, DigOUT Gnd. The signal comes from the pin 10,DigOUT4.

The signal operates a relay7, that switches 24V DC to the clutches, see pic.4.3

Figure 4.4: Signal connector J5, numbering

6up to 500mA7Omron G5SB-14, 5A, 30V DC

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4.3. Clutch Control

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5. Conclusion

5.1 Test driving and Discussion

After step by step starting up, it is stated, that all components work as theyshould. The arm shows clearly a double pendulum behaviour.

The shoulder joint has very little friction compared to the elbow joint, whichshows quite some damped behaviour. This is because of the rubber drive belt,which induces friction and because of the big moment acting on the shaft inthe elbow joint, caused by the belt tension, too.

Operating the first link at full speed is a problem at the moment. The power

supply falls into over voltage protection above the speed of ca. 260rpm, whichis about 60% of the dimensioned speed. The guess is that starting from zero-speed with full load causes transient phases, where the voltage exceeds the60V, for which the power supply is designed. Maybe some additional batteriesmight help reduce the peak voltage.

The MATLAB R codes used for test driving are contained in the data CD.

Application in a Robotic Quadruped

The initially mentioned usefulness of a clutched drive for a quadruped robotis not very big due to two main reasons.

First of all, unless intensive weight reduction is performed, the whole driveis much too heavy. The two drives weigh easily more than 10kg together.That is clearly more than the limit, that this drive can lift using this clutch1.Choosing stronger clutches involves in turn a massive weight increase.

Secondly the whole design is very bulky. The overall width is 0.8m. If four

1max. torque 17.5Nm

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5.2. Future Topics

of these drives are to be built into a robot, there won’t be any space left.Attempts to make the drive more compact cause more parts to be built in.

This is due to the special way the clutches have to be mount.

Research on the Benefits / Drawbacks of Active/Passive Drive

The concept of AP-control2 has to be studied yet. The base for further studyis present with the double pendulum robotic arm. Although in the momentit can only be operated in a feed forward manner, it will be very useful forresearch once it can be controlled with a feedback loop, that makes use of thehall sensors and takes the springy behaviour of the couplings into account.

5.2 Future Topics

These are some points, which have to be considered and solved in furthercourse of the project.

• A gripper should be designed and mount at the tip of the second link tobe able to grab and throw small objects.

• The set-up should be able to reach full speed. This involves analysing,why the over voltage protection on the power supply gets active andanticipating that. Either by installing additional power sources like bat-teries or by installing stronger power supplies.

• When top speed can be achieved, a safety cage should be installed aroundthe arm to avoid injury.

• The cable handling at the moment does not allow more than 3 full rota-tions. It should be stored more compactly.

• Design a faster operating system than MATLAB R. Preferably usingC++ coding on e.g. Visual Studio. This could enable the arm to offer anice platform for control tasks.

• Write a control algorithm, that is able to bring the arm to a certainposition, achieving at the same time the launch speed. One way to solveis to use the dynamic programming algorithm. Also, there is a modecalled interpolated position mode (IPM) on the EPOS2, that intended

2active / passive

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5.2. Future Topics

to do exactly, what is said above. It reaches at a certain time a certainposition and speed. This mode can be studied further.

• Get the springy behaviour of the couplings under control.

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5.2. Future Topics

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A. Appendix

Resources

• ASL workshop: http://www.asl.ethz.ch

• Maxon Motor: http://www.maxonmotor.ch

• Miki Pulley: http://www.mikipulley.co.jp/

• Maedler: http://www.maedler.ch

• Misumi: http://www.misumi-europe.com/

• Distrelec: http://www.distrelec.ch

• BIRL: http://www.birl.ethz.ch

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A.1. Parts List

A.1 Parts List

Parts list without screws, retaining rings and pins:

Maxon Motor

Quantity Part Description Product Nr.2 Motor: RE 40, 48V, 150W 1488772 Gear: GP 52, Ceramic Version, 15:1 2230842 Controller: EPOS2 70/10 3757112 Encoder: Encoder MR, Type L, 256 CPT 225783

2 Cable: EPOS power cable 2758292 Cable: EPOS motor cable 2758512 Cable: EPOS encoder cable 2759342 Cable: EPOS CAN-CAN cable 275926

Miki Pulley

Quantity Part Description Product Nr.

2 Electromagn. toothed clutch 546-12-34-NF 24V10 DIN

Distrelec

Quantity Part Description Product Nr.2 Angular-pos. sensor, Novotechnik RFC 4801-636-111-2012 Position marker, Novotechnik Z-RFC-P02

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A.1. Parts List

Misumi

Quantity Part Description Product Nr.1 Bearing with Housings, T-shaped BSHWA606ZZ-35-25

Maedler

Quantity Part Description Product Nr.2 Self-aligning Coupling LA, stainl. steel, B=10mm 602998421 Pulley AT10, 25mm width, 26 teeth 16832600

1 Pulley AT10, modified by ASL workshop 168326001 AT10 Timing Belt, 25mm width, 920mm 168712001 Pulley T2.5, 6mm width, 44 teeth 160244001 Pulley T2.5, modified by ASL workshop 160244001 T2.5 Timing Belt, 6mm width, 230mm 160606001 Shaft Nut w. Integral Locking Device M25x1,5 653544001 Clamping Set BAR, d=20mm, D=38mm 615420002 Clamping Set BAR, d=12mm, D=22mm 615412001 Clamp Collar Double-Split, Aluminium, d=18mm 623664181 Clamp Collars Single-Split, Aluminium, d=10mm 623661103 SKF Ball Bearing, d=10mm, D=26mm, B=8mm 6000-SKF3 SKF Ball Bearing, d=10mm, D=28mm, B=8mm 6001-SKF2 SKF Ball Bearing, d=10mm, D=32mm, B=10mm 6201-SKF2 SKF Ball Bearing, d=20mm, D=47mm, B=14mm 6204-SKF

BIRL

Quantity Part Description Product Nr.2 PCB Relay, 5VDC 9919031 Farnell

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A . 1 .

P a r t s

L i s t


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A.2. Pictures

A.2 Pictures

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A.2. Pictures

Figure A.1: The whole set-up

Figure A.2: The arm on the base

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A.2. Pictures

Figure A.3: Arm drive

Figure A.4: Clutch and coupling

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A.2. Pictures

Figure A.5: Encoder set-up

Figure A.6: Detail encoder

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A.2. Pictures

Figure A.7: Elbow joint

Figure A.8: Shoulder joint

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A.3. Data CD

A.3 Data CD

Contents

• Report in PDF format

• CAD files of all the components and the assembly created with NX 7.5

• Data sheets of the electric and electronic devices

• MATLAB R-code for test driving and executing the demonstration pro-gram

• Pictures, partly in higher resolution

• Movie

Brandle Dxc

Documents

Transcript of Brandle Dxc