与Allegro位置传感器IC的操纵杆

与Allegro位置传感器IC的操纵杆

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By Christophe Lutz and Andrea Foletto,
亚博棋牌游戏Allegro MicroSystems欧洲有限公司

介绍

操纵杆广泛应用人机接口(HMI)that simultaneously report information on direction and amplitude. Stick tracking is realized by use of a magnet and a magnetic
位置传感器。

本文档介绍了如何实现2D或3D磁传感器以获得具有明确行为的操纵杆。本说明提供了两个跟踪方法的见解：直接跟踪andR.atio tracking。直接的tracking offers a straightforward implementation, while ratio tracking offers excellent robustness to stick mechanical play. Finally, this application note assesses the relative robustness of these techniques to parameter variations (mounting and in-life).

操纵杆描述

Mechanically, a joystick consists of a stick that pivots through a ball joint on its base. Figure 1 provides a cross-sectional view of a joystick.

为了追踪杆的位置，磁铁集成在球的底部，以使球和磁体随着杆被致动时移动。磁性位置传感器应放置在磁铁下方合适的距离，表示为air gap。

Stick Tracking

操纵杆杆上的动作将影响传感器所感测的磁场。在本申请说明中，磁铁的磁化为轴向和指向（南极，北极）。如图2所示，杆位置的信息包含在X和Y方向上的感测的磁场中。

增加杆的倾斜度增加了感测信号，因为面内磁场分量增加。专注于操纵杆对倾斜的响应，θ., it is convenient to exclude directional information.

The stick position point in the position plot (represented by a black dot) is expected to move according to the tilt angle and in the same direction as the stick. Responsivity,Resp，应被视为从杆位置点到中心的距离，如图3所示，表示为：

R.可以表示x（当φ= 0°）或y（当方向是任意时的任何组合。位置图中的棒位置点的响应值定义为：

在实践中，响应性也取决于杆，φ的取向，但通常可以将这种依赖性排除在诸如气隙之类的其他参数之外。

如下一节中的证明，响应性与磁体到传感器的距离密切相关，因为它可以加剧或阻尼磁铁边界效应，短尺寸
不对称等。该距离通常称为气隙（Ag）。

对于操纵杆应用，空气隙无倾亚博尊贵会员斜，θ.= 0°。

气隙Constraints

Air gap as defined in Figure 2 is a key parameter in the application that will both affect the selection of sensor and the final responsivity of the stick. This parameter must comply with the following mechanical and magnetic constraints.

机械约束will provide a lower bound to the air gap for a cylindrical magnet that is not embedded in the ball of the joystick. This constraint ensures no contact between the rotating
部分和传感器。

通过考虑图4中的极限接触案，可以推导出最小气隙，AGMIN（机械）。

使用低灵敏度器件时应考虑机械下限。

磁性约束来自信号电平要求。传感器通常能够感测给定范围的磁场而不经历饱和度。对于正确的行为，重要的是确保传感器在实施过程中不饱和。在实践中，这种非饱和条件为气隙提供了额外的约束，AG_MIN（MAG），取决于传感器的灵敏度，磁体的形状和常离磁场，以及最大倾斜角，θ_最大限度。When considering a joystick consisting of a ball joint of 10 mm diameter, a cylindrical magnet of 1 T, diameter 5.4 mm, length 1 mm, and which can be tilted ofθ._最大限度= 25°, simulations lead to the minimum air gap values shown in Table 1.

表1：操纵杆磁间隙上的磁隙

传感范围（g）	AGMIN(MAG)
	No Saturation on x/y	没有饱和z
±500	1.5毫米	2.1 mm
±1000	0.9毫米	1.1毫米
±2000.	0.5 mm	机械有限

Generally, for joysticks that use only small tilt angles (θ._最大限度«25°），非饱和约束在Z轴相对于X / Y轴上更加限制。为此目的，Allegro已经开发出传感器，例如ALS31300，Z轴上具有不同的传感范围。

由于空气隙设置了信号的水平，因此定义了信号噪声比（SNR）。该应用程序定义SNR的最小值，从而定义了气隙的上限，Agmax（Mag）。

注意：应考虑安全裕度，以确保虽然具有由于制造，寿命漂移等有任何参数变化，但仍然可以在其允许的范围内停留。

直接和比率杆跟踪

如前所述，杆位置信息包含在X和Y轴上的感测磁场中。

直接的stick tracking plots stick position by using the data sensed in x and y directly. The simplicity and general accuracy of this technique is sufficient for most applications. Its major drawback is its vulnerability to dynamic air gap variations that may occur during the lifetime of the product. This variation is typically from vertical play of the stick. For instance, pressing on the stick may cause the stick position point in the position plot to jump to another value. A dynamic air gap reduction will always lead to an increase of the magnetic field sensed.

为了对抗这种不需要的效果，可以实现比率杆跟踪技术。当气隙变化时，X和Y上感应的值将更多或更少具有与在Z轴上的值感测的相同的变化。因此，使用x / z和y / z而不是单独的x和y将显着降低气隙依赖性。虽然比率棒跟踪更加稳健，但它确实影响了响应曲线。

该转换只需重新缩放位置图（见图5）。直接杆跟踪包含的所有结果都可以通过X / Z（分别的Y / Z）代替X（分别Y）来直接地转换为比率杆跟踪。作为示例，距离杆位置点到位置绘图中心的距离变为：

Because of this, all joystick corrective behavior post-processing can be applied to both tracking methods. The difference in responsivity and relative robustness to variations differentiates the two tracking methods.

操纵杆的回应

Responsivity of the joystick describes the correlation between the mechanical movements of the stick and its stick position point on the position plot as output by the sensor. The air gap affects this relationship.

为了解释气隙的效果，用于操纵杆的仿真，由直径为10 mm的球接头，圆柱形磁体为1 T，直径为5.4mm，长度为1mm，可以倾斜θ_最大限度= 25°, gives results as shown in Figure 6 and Figure 7 for direct and ratio stick tracking, respectively.

从图6中，可以推导出直接跟踪的以下属性：

• 大气隙导致倾斜角度范围几乎线性响应。

• 低气隙导致操纵杆，其用小θ角度线性响应，而特征变为大角度的非线性。此功能在需要精度和范围（高角度高响应度）的应用中很有趣。

从图7中，可以推导出比率跟踪的以下属性：

• 由于曲线的叠加所示，气隙的效果被巨大地降低。
• 无论气隙如何，操纵杆响应都是线性的，对于小θ角度，而特征变为大角度的非线性。此功能在需要精度和范围（高角度高响应度）的应用中很有趣。

The response curve nonlinearity is due mainly to the nonlinearity of the magnetic field with position and not to the sensing of the sensor. Nonlinearities can be neglected for small values of θ_{最大限度。}

操纵杆对变化的鲁棒性

从先前考虑（约束和行为）寻址的空气隙，传感器的位置完全确定。

现在，两种跟踪技术可以根据稳健性对抗因子而面临：

• 安装精度
• Mechanical play

Due to physical limitations, the sensing elements of multi-axis position sensors cannot sense the magnetic field components at the exact same location. This tiny built-in asymmetry leads to different responses in different directions. Likewise, error plots may reflect this asymmetry.

The following parameters drifts have been considered:

• 传感器相对于杆轴移位。
• 磁铁相对于杆轴移位。
• 相对于其参考值，气隙小或更大。

The error is quantified as the distance between the ideal and drifted position of the stick position point. To compare direct and ratio stick tracking techniques, their errors have been respectively expressed as a percentage of their full-scale (FS) values, namely r_最大限度and r_RATIO(MAX)。

从这些地块中，可以进行若干观察结果：

• 由于传感器位移，大的倾斜角将始终加剧错误。
• 比率跟踪对气隙变化更加坚固。
• 直接的tracking is more robust to in-plane displacements than ratio tracking.

表2总结了最大误差，并描述了定性地对位置绘图上的错误的反射。

传感器原始数据可以被处理以减少系统误差（由于传感器或磁铁安装），但不会防止寿命（由于机械播放）漂移。

Error per unit displacement:

请注意，最大误差取决于最大倾斜角θmax和操纵杆的尺寸。

Table 2: Maximum errors due to parameters drifts, no post-processing

Error %FS/0.1 mm	直接的 追踪	比率 追踪	定性效果
气隙 0.1 mm in z	10.8	1.6	改变响应性
Sensor 0.1 mm in x 0.1 mm in y	7.0 7.0	16.5 16.5	Adds offset in position plot
磁铁 0.1 mm in x 0.1 mm in y	5.5 4.6	15.5 4.4	改变响应性; φSENSED从φ漂移

The previous table leads to the following total error for an optimally compensated joystick with stick vertical play much greater than horizontal plays:

Table 3: Maximum errors due to parameters drifts, with post-processing

错误，％fs	直接跟踪	比率跟踪
气隙 0.1 mm in z	10.8× vertical play	1.6×垂直播放
Sensor 0.1 mm in x 0.1 mm in y	〜0 横向戏剧有限公司	〜0 横向戏剧有限公司
磁铁 0.1 mm in x 0.1 mm in y	〜0 横向戏剧有限公司	〜0 横向戏剧有限公司

Generally, the direct stick tracking method will exhibit sufficient immunity to misplacements during mounting, though control of air gap is required.

假设由于补偿后处理而导致的误差减少。一旦纠正了这种系统错误，系统只能由于机械播放而具有错误。在实践中，
操纵杆部分不太可能从每个不移动her horizontally, e.g. the sensor location with respect to the stick axis will not vary during product’s life. What can change is the air gap value when
the user applies pressure on the stick either intentionally (“crouch”) or not. Ratio stick tracking is therefore desirable to dampen the air gap variation error and have a highly accurate joystick.

结论

The joystick is a device having a stick tracked by a magnetic sensor through a magnet attached to a ball joint.

可以从操纵杆结构特征生成几种操纵杆行为（无论后处理）。如上所述，气隙将是线性度和信号的关键参数
等级。气隙不能小于机械和磁性所限定的阈值。

已经提出了直接和比率杆跟踪技术;表4总结了其关键特性：

表4：跟踪方法对比表

追踪	直接的	比率
Position Plot	X，Y.	x/z, y/z
ag min。	没有 saturation on x and y	没有 饱和在x，y和z上
AG Max.	受到SNR的限制	受到SNR的限制
Linearity with Tilt	高效改善	需要帖子 - Processing
精度和范围	在低AG改善	全部AG
机械约束 Without Post- Processing	AG Control	传感器和磁铁 放置
机械约束 With Post-Processing	限制水平 垂直戏剧	Limit horizontal plays
AG dependence	Yes	No

Generally, for an application that does not require extreme precision, a direct stick tracking method will be sufficient. To make a precision joystick, it might be necessary to use a ratio stick
跟踪方法后处理（如果安装精度尚未足够）。该选项提供低气隙依赖性，并创建一个非常精确和稳健的操纵杆。

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