Joystick with Allegro Position Sensor IC

Joystick with Allegro Position Sensor IC

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

Introduction

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
position sensor.

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).

Joystick Description

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.

To track the position of the stick, a magnet is integrated on the bottom of the ball in order that the ball and magnet move as a unit when the stick is actuated. A magnetic position sensor should be placed beneath the magnet at a suitable distance, denoted asair 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。

Increasing the tilt of the stick increases the sensed signal, since the in-plane magnetic field components are increased. To focus on the responsivity of the joystick with respect to the tilt,θ，排除方向信息是方便的。

位置图中的杆位置点（由黑点表示）预计将根据倾斜角和与棍子相同的方向移动。响应性，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：

In practice, responsivity is also dependent on the orientation of the stick, φ, but this dependence can usually be excluded with respect to other parameters such as air gap.

As will be demonstrated in the next section, responsivity is closely related to the distance from the magnet to the sensor since it can exacerbate or dampen magnet border effect, short-scale
不对称等。该距离通常称为气隙（Ag）。

For joystick applications, air gap is defined at no tilt,θ= 0°。

气隙限制

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.

机械约束将为不嵌入操纵杆的球中的圆柱形磁体提供下限的气隙。该约束确保旋转之间没有接触
部分和传感器。

Minimum air gap, AGMIN(MECH) can be deduced by considering the limit contact case in Figure 4.

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), depending on the sensitivity of the sensor, the shape and remanent magnetic field of the magnet, and the maximum tilt angle, θ_MAX。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_MAX= 25°，模拟导致表1中所示的最小气隙值。

表1：操纵杆磁间隙上的磁隙

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

Generally, for joysticks that use only small tilt angles (θ_MAX«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。

直接的and Ratio Stick Tracking

As mentioned previously, stick position information is contained in the sensed magnetic field on the x and y axes.

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。

This transformation simply rescales the position plot (see Figure 5). All results contained by direct stick tracking can be straightforwardly translated to ratio stick tracking by substituting x (respectively y) by x/z (respectively y/z). As an example, the distance from the stick position point to the center of the position plot becomes:

因此，所有操纵杆纠正行为都可以应用于两种跟踪方法。对变化的响应性和相对稳健性的差异区分了两种跟踪方法。

操纵杆的回应

操纵杆的响应性描述了杆的机械运动与其杆位置点之间的位置图，其位置图是传感器的输出。气隙会影响这种关系。

To explain the effect of the air gap, simulation for a joystick made 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 of θ_MAX= 25°，可分别提供如图6和图7所示的结果，分别用于直接和比率杆跟踪。

从图6中，可以推导出直接跟踪的以下属性：

• Large air gap leads to almost linear response over the tilt angle range.

• 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。
• Regardless of the air gap, the joystick response is linear for small θ angles, while the characteristic becomes nonlinear for large angles. This feature is interesting in application requiring both precision and range (high responsivity at high angle).

响应曲线非线性主要是由于磁场的非线性与位置而不是传感器的感测。对于θ的小值，可以忽略非线性_MAX.

操纵杆对变化的鲁棒性

The air gap addressed from previous considerations (constraints and behavior), the position of the sensor is fully determined.

Now, the two tracking techniques can be confronted in terms of their robustness against variations due to:

• Mounting precision
• Mechanical play

由于物理限制，多轴位置传感器的感测元件不能感测磁场分量在完全相同的位置。这种微小的内置不对称导致不同方向的不同响应。同样，错误图可能反映这种不对称性。

已考虑以下参数漂移：

• 传感器displaced with respect to the stick axis.
• 磁铁相对于杆轴移位。
• Air gap smaller or larger with respect to its reference value.

错误被量化为杆位置点的理想和漂移位置之间的距离。为了比较直接和比率棒跟踪技术，它们的错误被分别表示为它们的全尺度（FS）值的百分比，即r_MAXand r_{比率（最大）}。

From these plots, several observations can be made:

• Large tilt angle will always exacerbate the error due to sensor displacements.
• Ratio tracking is more robust to air gap variations.
• 直接跟踪对面内位移比比率跟踪更强大。

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。

每单位位移时出错：

Note that the maximum error depends on the maximum tilt angle θMAX and on the dimensions of the joystick.

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

Error %FS/0.1 mm	直接的 Tracking	Ratio Tracking	Qualitative Effects
Air Gap 0.1 mm在z	10.8	1.6	Changes responsivity
传感器 0.1 mm in x 在y中0.1毫米	7.0 7.0	16.5 16.5	在位置绘图中添加偏移量
Magnet 0.1 mm in x 在y中0.1毫米	5.5 4.6	15.5 4.4	改变响应性; φSENSED从φ漂移

前面的表格导致最佳补偿操纵杆的总误差，其杆垂直播放远大于水平播放：

表3：参数漂移引起的最大误差，后处理

Error, %FS	直接跟踪	Ratio Tracking
Air Gap 0.1 mm在z	10.8×垂直播放	1.6×垂直播放
传感器 0.1 mm in x 在y中0.1毫米	~0 horizontal play limited	~0 horizontal play limited
Magnet 0.1 mm in x 在y中0.1毫米	~0 horizontal play limited	~0 horizontal play limited

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

Assume the error due to mounting is reduced by compensative post-processing. Once this systematic error is corrected, the system can only have errors due to mechanical plays. In practice, the
操纵杆部件不太可能水平彼此移动，例如，传感器位置相对于杆轴在产品的寿命期间不会变化。可以改变的是气隙值
用户有意地对杆上的压力（“克劳奇”）应用于杆上。因此，希望粘合跟踪是希望抑制气隙变化误差并具有高精度的操纵杆。

Conclusion

操纵杆是具有由磁传感器通过附接到球接头的磁体跟踪的杆的装置。

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。

直接的and ratio stick tracking techniques have been presented; Table 4 summarizes their key features:

Table 4: Tracking Method Comparative Table

Tracking	直接的	Ratio
位置情节	X，Y.	x/z, y/z
ag min。	Limited by no saturation on x and y	Limited by no 饱和在x，y和z上
ag max。	Limited by SNR	Limited by SNR
与倾斜的线性	高效改善	Requires Post- 加工
Precision and Range	在低AG改善	Present at all AG
Mechanical constraints 没有帖子 - 加工	AG控制	传感器和磁铁 放置
Mechanical constraints 随着后处理	限制水平 vertical plays	Limit horizontal plays
AG dependence	是的	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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