Shock robustness of Mobile devices with HDD. Jan Ruigrok

Transcription

1 Shock robustness of Mobile devices with HDD Jan Ruigrok 1

2 Content of this presentation 1. Introduction MP3-player 2. Development of new test method (pendulum) Requirements Solved problems 3. Robustness test of HDD Current test New test method Results 4. Recommendations 2

3 1: Problem When do the HDD s of MP3-players fail? Testing current designs Improving designs 3

4 1: Displacement, velocity and acceleration during drop Important parameters Drop height Impact velocity Velocity change Pulse time Maximum acceleration Contact stiffness 4

5 1: Hard Disc Drive Operating: 200 G, 1ms Half sine pulse Non-operating: 2000 G, 1ms half sine pulse 5

6 1: Current protection Buffer HDD with snubbers Rubber cushioning which can deform during impact Pulse time increases Maximum acceleration decreases 6

7 2: Robustness test Drop height 6 orientations Performance tests Turn on/off test Data transfer rate 7

8 2: new test method Measure drop height Control on impact orientation Acceleration measurements Evaluate different protections Analyse effect of shock on HDD 8

9 2: Test results acceleration velocity 9

10 2: Test results acceleration velocity e=1 e=0 10

11 2: Problem with Pendulum Maximum drop height of pendulum lower than the drop height measured with the free fall test During the free fall little offsets occur due to rotations These offsets influence the maximum acceleration of the HDD 11

12 2: 3-D results Maximum acceleration on flat impacts Behaviour around flat impacts important 12

13 2: Results 13

14 2: Summary of pendulum results Pendulum makes it possible to have control on impact orientation Flat impact not always worst case Maximum acceleration can change due to offsets First impact not always most severe impact Velocity change decreases with an offset Applying an offset with pendulum gives the same result as the free fall test 14

15 3: Accelerations on HDD I-pod mini Drop height: 50 cm Measured: 5000 G, 0.2 ms No failure Spec:2000 G, 1 ms Other players show same kind results. Much higher accelerations before failure of HDD. 15

16 3: Damage Boundary Curve DBC Critical velocity change Critical acceleration Failure if both values are higher. 16

17 3: Fixture HDD placed inside fixture Pendulum is used to impact fixture Impact time can be changed by changing contact area 17

18 3: Calibration of fixture Acceleration measurements on fixture Every line represents one contact area. Increasing drop height, larger acceleration Increasing drop height, larger velocity change With short pulses and high drop heights noise on acceleration measurements 18

19 Supplier A A max =2000 G, 1ms v =6.3 m/s Supplier B A max =1250 G, 1ms v =6.1 m/s v more important for MP3- player 3: DBC results 19

20 3: Effect of buffering A small buffer does not reduce the acceleration below the critical acceleration Only possible with a deformation of several mm 20

21 3: Effect of bouncing Lower restitution coefficient increases the drop height Drop height could be increased with factor 2.6 for Philips HDD084. Reducing velocity change does also reduce the maximum acceleration 21

22 3: DBC conclusions Critical velocity can be measured with fixture Critical acceleration can be measured if the impact velocity of the pendulum is increased Velocity change more important for robustness MP3- player Reducing the bouncing could improve drop height Possible to evaluate effect of shock on HDD 22

23 4: Future research Higher impact velocities for pendulum. For both robustness test as for the DBC test. Influence of offset on velocity change Influence of material on restitution coefficient 23