ImageView上的TranslateAnimation不起作用

我试图使用TranslateAnimation上ImageView,但ImageView根本不会移动.运行项目时没有任何反应.这是我的代码:

import android.app.Activity;
import android.os.*;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.TranslateAnimation;
import android.widget.ImageView;

public class MainActivity extends Activity {
ImageView a;
TranslateAnimation pengesat;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    a = (ImageView) findViewById(R.id.imageView3);
    pengesat = new TranslateAnimation( 0.0f,  1.0f,  0.0f,  0.0f );
    pengesat.setDuration(5000);
    pengesat.setRepeatCount(1);
    pengesat.setInterpolator(new AccelerateInterpolator());
    Thread myThread= new Thread(new Runnable(){
        @Override
        public void run() {
            a.post(new Runnable() {
                @Override
                public void run() {
                    a.startAnimation(pengesat);
                }
            });
        }
    });
    myThread.start();
  }
}

这是我的xml代码:

我究竟做错了什么？