Unit 4 Reading is fun

Unit 4 Reading is fun

5.选词填空完成句子。

make read buy take do

1)I’m going to ___a survey about our teather’s favourite books.

2)We are e going to ___ some photos in the park.

3)There is a library near the park. We can ___ books in it.

4)Children’s Day is coming. The students are going to ___some posters.

5)My mother wants to ___some food in the supermaket.

6.选词填空完成句子。

What Who Where Why Whose

1)- ___magazine is this? -It’s Mr Li’s.

2)- ___is the film about? -It’s about wild geese.

3)- ___is Alice now? -She’s on tne second floor.

4)- ___has a dictionary? -Joe has one.

5)- ___do you like reading books?

- Because I can learn about the world in books.

7.选择填空。

1）-_____you like this storybook? -Yes （）

A.Do

B.Are

C.Have

2)I’m going to ______a story every day. （）

A.reading

B.look

C.read

3)They are going to buy some books_____. （）

A.at the bookshop

B.in the restaurant

C.in the library

4)- Are these _____books? （）

- Yes, they’re_____.

A.you,yours

B.your,mine

C.yours,mine

5）- Why do you like this picture? - ______. （）

A.Because it’s beautiful

B.I like it too.

C.Beacause it’s enough. 6）They are going to do a _____ about people’s favourite drinks. （）

A.survey

B.find

C.see

7）- Who is the man _____? （）

- He’s my uncle.He’s waiting for me.

A.on there

B.over there

C.welcome

8)The _____ writes a lot of storybooks. All the children like his stories. （）

A.pilot

B.singer

C.writer

9)The children are going to _____? （）

A.take out

B.put out

C.act out

10)What is he going to _____? （）

A.buying

B.buys

C.buy

8.用所给词的适当形式填空。

1）-What _____(be) you doing?

-I’m _____(take) some photos.

2)Mr Chen _____(like) reading. He is going to ___(read) a storybook at the weekend.

3)-Where is your sister? -She’s on the _____(two) floor.

9.阅读短文，判断句子正误。正确的用T表示，错误的用F表示。

My name is John. I’m a student at No.2 Primary School(小学). I like reding books very much. My favourite library is Moon Library. It is not far form my homr. I always go there on foot. The library is big and quiet. On the ground floor, there are newspaper and magazines. On the first floor,there are all kinds of books. People can read there. They can also borrow(借) the books home. Sometimes I go to the library with my friends. I’m going to read a storybook in the library this weekend.

1)John is a student. ( )

2)John likes riding bikes. （）

3)John always goes to Moon Library on foot. ( )

4)Sometimes John goes to the library with his family. ( )

5)John is going to read a picture book this weekend. ( )

____________________________________________________________________

2)what are Jill’s favourite books?

____________________________________________________________________

3)who is in the library?

____________________________________________________________________

4)where is Danny now?

____________________________________________________________________

5)Does Ben like storybooks best?

____________________________________________________________________

清华大学《控制工程基础》课件-4

则系统闭环传递函数为 假设得到的闭环传递函数三阶特征多项式可分解为 令对应项系数相等，有 二、高阶系统累试法 对于固有传递函数是高于二阶的高阶系统，PID校正不可能作到全部闭环极点的任意配置。但可以控制部分极点，以达到系统预期的性能指标。 根据相位裕量的定义，有 则有 则 由式可独立地解出比例增益，而后一式包含两个未知参数和，不是唯一解。通常由稳态误差要求，通过开环放大倍数，先确定积分增益，然后计算出微分增益。同时通过数字仿真，反复试探，最后确定、和三个参数。 设单位反馈的受控对象的传递函数为 试设计PID控制器，实现系统剪切频率 ，相角裕量。 解： 由式,得 由式,得 输入引起的系统误差象函数表达式为

令单位加速度输入的稳态误差，利用上式，可得 试探法 采用试探法，首先仅选择比例校正，使系统闭环后满足稳定性指标。然后，在此基础上根据稳态误差要求加入适当参数的积分校正。积分校正的加入往往使系统稳定裕量和快速性下降，此时再加入适当参数的微分校正，保证系统的稳定性和快速性。以上过程通常需要循环试探几次，方能使系统闭环后达到理想的性能指标。 齐格勒－尼柯尔斯法 （Ziegler and Nichols ） 对于受控对象比较复杂、数学模型难以建立的情况，在系统的设计和调试过程中，可以考虑借助实验方法，采用齐格勒－尼柯尔斯法对PID调节器进行设计。用该方法系统实现所谓“四分之一衰减”响应（”quarter-decay”），即设计的调节器使系统闭环阶跃响应相临后一个周期的超调衰减为前一个周期的25%左右。 当开环受控对象阶跃响应没有超调，其响应曲线有如下图的S形状时，采用齐格勒－尼柯尔斯第一法设定PID参数。对单位阶跃响应曲线上斜率最大的拐点作切线，得参数L 和T，则齐格勒－尼柯尔斯法参数设定如下： (a) 比例控制器： (b) 比例－积分控制器： ， (c) 比例－积分－微分控制器： ， 对于低增益时稳定而高增益时不稳定会产生振荡发散的系统，采用齐格勒－尼柯尔斯第二法(即连续振荡法)设定参数。开始只加比例校正，系统先以低增益值工作，然后慢慢增加增益，直到闭环系统输出等幅度振荡为止。这表明受控对象加该增益的比例控制已达稳定性极限，为临界稳定状态，此时测量并记录振荡周期Tu和比例增益值Ku。然后，齐格勒－尼柯尔斯法做参数设定如下： (a) 比例控制器：