一、什么是传送带跟踪？
传送带跟踪通常用于食品和包装行业。典型的应用有：跟踪巧克力、糖果、面包将其放进盒子内，或者摆放在一起。传送带不停的运动，根据机器视觉给出的位置信息，引导机器人进行抓取任务。下图是一个示意图： 
待抓取的物体part经过相机拍照处理后，随着传送带带到机械手抓取范围内，机器人将会抓取物体并将其放到指定位置。
二、传送带跟踪过程
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视觉系统拍照
等待工件进入抓取区域
进行抓取
同步阶段
放置
视觉系统拍照的目的是为了给出工件在机械手坐标系下的瞬时位置，此时机械手可能尚未进入可抓取区域，机械手需要等待工件进入并进行抓取，同步阶段是为了保证物体已经被抓起，最后机械手将会完成抓取并放置的动作。
三、抓取策略
传送带速度如何设置？
- 如果工件比较密集，机械手可能会出现“漏抓”现象，适当降低传送带速度可以避免；
- 如果工件比较稀疏，机械手可能会出现“偷懒”现象，适当提升传送带速度可以避免；
3.1 PID式抓取策略
这一种形式机械手的目标位置实时刷新，使得机械手末端速度与皮带速度完全一致即可完成抓取。
3.2 位置预测策略
这个策略简单来说，就是在工件运行方向找到一个点，这个点使得机械手到该点的时间恰好等于传送带到该点的时间。如何寻找这个点是策略的主要目的，抓取点求取过程如下（注意这是建立在机械手坐标系
X
X
X轴和皮带运动方向同向的基础上的）。
工件进入视觉系统瞬间，相机将会给出此刻工件位置
P
P
P，经过
t
1
t_1
t1时间后，相机将会到达点
M
M
M，设传送带速度恒定，大小为
V
V
V，则有：
t
1
=
P
M
V
t_1=\frac{PM}{V}
t1=VPM
再来看机械手的运动，假设此时机械手的位置为
S
S
S，经过
t
2
t_2
t2时间机械手末端到同一个点
M
M
M，所以有：
t
2
=
f
(
S
M
)
t_2=f(SM)
t2=f(SM)
f
f
f计算规划时间的函数，如果
t
1
=
t
2
t_1=t_2
t1=t2，此时的
M
M
M就是抓取点：
P
M
V
−
f
(
S
M
)
=
0
\frac{PM}{V}-f(SM)=0
VPM−f(SM)=0
M
M
M点的坐标为
(
x
m
,
y
m
)
(x_m,y_m)
(xm,ym)，
P
P
P点的坐标为
(
x
p
,
y
p
)
(x_p,y_p)
(xp,yp)，因为传送带运动方向为“纯”
X
X
X方向，所以有：
M
=
(
x
m
,
y
p
)
M=(x_m,y_p)
M=(xm,yp) 显然
P
M
PM
PM是一个关于数
x
m
x_m
xm的方程，同理
S
M
SM
SM亦是如此。设他们之间的关系为
P
M
=
g
(
x
m
)
S
M
=
h
(
x
m
)
PM=g(x_m)\quad SM=h(x_m)
PM=g(xm)SM=h(xm)，进而：
g
(
x
m
)
V
−
f
[
h
(
x
m
)
]
=
0
\frac{g(x_m)}{V}-f[h(x_m)]=0
Vg(xm)−f[h(xm)]=0 再抽象一下：
t
(
x
m
)
=
0
t(x_m)=0
t(xm)=0 求抓取点问题转换成求上述方程的零点，求零点的方法可以通过二分法计算，假设抓取的上限为
U
U
U，抓取的下限制为
D
D
D，计算流程如下： 
首先检查再指定上下游是否有解，如果没有解，直接退出循环；如果有解，根据二分法求出解的范围，每次求解的时候需要判断是否满足我们的误差要求
x
e
r
r
x_{err}
xerr，如果不满足继续二分，如果满足退出循环，此时的
x
d
x_d
xd或者
x
u
x_u
xu为所求抓取点的位置。
[1]王铮, 戴坚锋, 钱振宇,等. 面向传送带作业系统的机器人目标跟踪与抓取策略研究[J]. 计算机测量与控制, 2016, 24(11):6.
