Development report
Current information of Magnetfabrik Bonn
06/2015
Multipole magnets for angle encoders
State of the art
System with 2 sensors
B1 = b•sin(a)
Hall
sensors
B2 = b•cos(a)
n-pole
magnet
() ( )
( )
() ( )
B1
sin(a)
= arctan
B2
cos(a)
Angle = arctan
⇒ Angle ∈ - π2 ; π2
Angle = arctan 2
B1
B2
= arctan 2
sin(a)
Sensitive to:
• sensor positioning
• external magnetic field
cos(a)
⇒ Angle ∈( - π ; π )
System with 4 sensors / spaced by 1/2 pole pitch
B1 = b•sin(a)
B2 = b•sin(a + π
2 ) =b•cos(a)
B3 = b•sin(a + π ) =-b•sin(a)
3
B4 = b•sin(a + 2π ) =-b•cos(a)
( )
Angle = arctan 2
B1 - B3
B2 - B4
Hall
sensors
n-pole
magnet
Compensates:
• homogeneous external magnetic field
• sensor & magnet temperature drifts
• sensor-magnet distance
Detriments:
• phase error
• material costs
• sensor line along whole pole pair
Multipole magnets for angle encoders
New approach / Patent pending
System with 3 sensors / spaced by 2/3 pole pitch
Sensor signal
B1 = b•sin(a)
B2 = b•sin(a + 2π
3 + d2)
2π
B3 = b•sin(a - 3 + d3)
Hall
sensors
n-pole
magnet
Phase error compensation
B1* = B1 - k1* •(B2 - B3)
B2* = B2 - k2* •(B3 - B1)
B3* = B3 - k3* •(B1 - B2)
where ki* =
di
√3
, di = phase error
Offset compensation
D1 = B2* - B3*
D2 = B3* - B1*
D3 = B1* - B2*
Sensor position
(
(
(
Z1 = arctan 2
Z2 = arctan 2
Z3 = arctan 2
√3 • D1
D2 - D3
+
π
3
√3 • D2 π
D3 - D1 3
√3 • D3
D1 - D2
-π
)
)
)
(Z + Z + Z ) • 2
Mechanical angle = 1 2 3
3•n
Applications:
• motor commutation
• magnetic encoding
• steering angle and torque sensing
• rotational angle measurement
• rotational speed sensing
Compensates:
• homogeneous external magnetic field
• sensor & magnet temperature drifts
• sensor-magnet distance
• non sinusoidal B(a)
Benefits vs. 4 sensors:
• smaller chip size
• symmetric layout
• lower sensitivity to field deviation
Use our expertise in developing customised multipole magnets for your specific application.
Challenge us! Further information/contact:
Phone +49 228 72905-0
E-Mail: [email protected]
Magnetfabrik Bonn GmbH
Dorotheenstraße 215 • D-53119 Bonn
Telefon +49 228 72905-0 • Telefax +49 228 72905-37
[email protected] • www.magnetfabrik.de