带Allegro位置传感器IC的操纵杆

带Allegro位置传感器IC的操纵杆

下载PDF版本

由Christophe Lutz和Andrea Foletto，
雷竞技竞猜下载Allegro MicroSystems欧洲有限公司

介绍

操纵杆是广泛使用的人机界面（HMI），可同时报告方向和振幅信息。利用磁铁和磁头实现了棒跟踪
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：直接跟踪和R.atio tracking。直接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).

操纵杆说明

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.

为了跟踪斗杆的位置，磁铁集成在球的底部，以便在操纵斗杆时球和磁铁作为一个单元移动。磁性位置传感器应放置在磁铁下方适当的距离处，表示为气隙。

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, 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，响应度还依赖于棒的方向φ，但这种依赖性通常可以排除在其他参数（如气隙）之外。

下一节将演示，响应度与磁铁到传感器的距离密切相关，因为它会加剧或抑制磁铁边界效应，即短尺度效应
不对称等。该距离通常称为气隙（Ag）。

对于操纵杆应用，气隙定义为雷竞技最新网址不倾斜，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。

最小气隙AGMIN（MECH）可以通过考虑图4中的极限接触情况来推导。

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_{最小值（MAG）}，取决于传感器的灵敏度、磁铁的形状和剩余磁场以及最大倾角θ_马克斯。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_马克斯= 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（磁）
	No Saturation on x/y	z上没有饱和
±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_马克斯«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。

直接和比例棒跟踪

如前所述，斗杆位置信息包含在x和y轴上的感应磁场中。

直接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。

这个转换只是重新缩放位置图（参见图5）。用x/z（y/z）代替x（y/z）可以直接转化为比例跟踪。例如，从斗杆位置点到位置图中心的距离变为：

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.

为了解释气隙的影响，模拟了一个由直径为10毫米的球头、直径为5.4毫米、长度为1毫米、可倾斜θ的圆柱形磁铁组成的操纵杆_马克斯= 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：

• 大的气隙导致倾斜角度范围内几乎呈线性响应。

• 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。
• 无论气隙大小，小θ角时操纵杆响应为线性，大θ角时操纵杆响应为非线性。该特性在要求精度和范围（高角度下的高响应度）的应用中非常有趣。

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_最大值。

操纵杆对变化的鲁棒性

气隙从以前的考虑（约束和行为）解决，传感器的位置是完全确定的。

现在，这两种跟踪技术在其抗变化的鲁棒性方面面临挑战，因为：

• 安装精度
• 机械玩

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:

• 传感器相对于斗杆轴发生位移。
• 磁铁相对于杆轴移位。
• 相对于其参考值，气隙更小或更大。

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_马克斯和R._RATIO(MAX)。

从这些曲线图中，可以得出几个观察结果：

• 由于传感器位移，大的倾斜角度总是会加剧误差。
• 比率跟踪对气隙变化更为稳健。
• 直接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度θMAX和操纵手柄的尺寸。

表2：参数漂移导致的最大误差，无后处理

Error %FS/0.1毫米	直接 跟踪	比率 跟踪	质量效应
气隙 0.1 mm in z	10.8	1.6	变化响应度
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	变化响应度; 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 水平播放限制	~0 水平播放限制
磁铁 0.1 mm in x 0.1 mm in y	~0 水平播放限制	~0 水平播放限制

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

假设安装误差通过补偿后处理减小。一旦纠正了系统误差，系统就只能因机械间隙而产生误差。在实践中
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
用户应用压力棒强度ntionally (“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
水平。气隙不能小于机械和磁性所限定的阈值。

介绍了直接和比率棒跟踪技术；表4总结了它们的主要特点：

表4：跟踪方法对照表

跟踪	直接	比率
Position Plot	X，Y.	x/z、y/z
ag min。	不受限制 saturation on x and y	不受限制 饱和在x，y和z上
AG Max.	受信噪比限制	受信噪比限制
Linearity with Tilt	高效改善	Requires Post- Processing
精度和范围	在低AG改善	在所有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 垂直播放	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。

版权所有©2018，Allegro雷竞技竞猜下载 Microsystems，LLC
The information contained in this document does not constitute any representation, warranty, assurance, guaranty, or inducement by Allegro to the customer with respect to the subject matter of this document. The information being provided does not guarantee that a process based on this information will be reliable, or that Allegro has explored all of the possible failure modes. It is the customer’s responsibility to do sufficient qualification testing of the final product to insure that it is reliable and meets all design requirements.
Copies of this document are considered uncontrolled documents.